V
Stbmfjj Annual Juport
OF THE
AERONAUTICAL SOCIETY
OF
GREAT BRITAIN
FOES THE YEAR 1872,
PRINTED BT
HENRY S. RICHARDSON,
GREENWICH,
Kryroilnccil nml /oioteil pliololitho offset for I ‘KTK.lt All R RAY HlU, ( I’lllllisliers) I.TI).
73 Sl.OANK AVKXl'K London* s.W.3 1 056
ll/l permission of the Royal Aeronautical Society
M.U>K AM) PKIXTK1) IN UJKKAT IIKITA1N 11V |). i(, IIIUMAN A SON'S I.TL)., SKOMK
THE
AERONAUTICAL SOCIETY OF GREAT BRITAIN.
Prcgfocnt,
HIS GRACE THE DUKE OF ARGYLL, K.T. UicE-Ipre«it)entg,
HIS GRACE THE DUKE OF SUTHERLAND. RIGHT HON. THE EARL OF DUFFERIN.
LORD RICHARD GROSVENOR, M.F.
^anomro Secretary,
FRED. W. BREAREY, Esq.
^oaoratu Solicitors,
Messrs. MATTHEWS & Gl^EETHAM, 26, Bedford Row, w.o.
(Council,
A. ALEXANDER, Esq., C.E., M.A., Sheffield.
FRED. VV. BREAREY, Esq., Maidenstone Hill, Blackheath, 8.E. Sir CHARLES T. BRIGHT, F.K.A.S., Lancaster Gate.
CHARLES BROOKE, Esq., ALA., F.R.S., 16, Fitzroy Square, W. JOHN BROWNING, Esq., F.R.A.S., F.R.M.S., 111, Miuories, E. HUGH W. DIAMOND, Esq., M.D., F.S.A., Twickenham. JAMES GLAISIIER, Esq., F.R.S., F.R.A.S., Blaeklmath. Rear-Admiral Lord JOHN HAY, C,B 119, Piccadilly.
W. H. LE FEUVRE, Esq., C.E., F.lt.G.S., 68, Bedford Gardens, Kensington, W.
MAGNUS OHREN, Esq., A.I.C.E., Lower Sydenham, S.E.
Lord LINDSAY, 47, Brook Street, W.
F.'H. WENIIAM, Esq., C.E., V.P.R.M.S., Padnal Hall, Chad well, Essex.
HENRY WRIGHT, Esq., Stafford House, St. James’.
WITH POWER TO ADD TO THEIR NUMBER.
Member’s Subscription, XI. Is. per annum, dating from the day of Election. Ladies may become Associates upon the same terms.
<$*b.entjj Annual $3Upod
OT THB
AERONAUTICAL SOCIETY OF GREAT BRITAIN,
FOR THE YEAR 1872.
Containing an Account of the Proceedings, and a Selection from the Papers and Communications* received by the Society during the year, with concluding Remarks upon the present state of the Science.
A General Meeting of the Members of this Society was held in the Theatre of the Society of Arts, John Street, Adelphi, on Tuesday evening, the 18th inst. Mr. James Glaisher, F.R.S., presided.
A new machine, constructed under the direction of the Society, for measuring the relation between the velocity and pressure of the wind, was exhibited.
At the request of the Chairman,
The minutes of the previous meeting were read by Mr. F. W. Brearey, the Hon. Secretary.
* The Council, in publishing any paper which may have been read or communicated, disclaim any intention of endorsing the views of their respective Authors. It is with the bolief that here and there a hint may be conveyed which may prove of use to those of the members who may be practically engaged in overcoming the acknowledged difficulties of the problem to be solved, that some of the papers have been published, which otherwise would appear hardly to justify their reproduction.
6
AERONAUTICAL SOCIETY
The Chairman : Ladies and Gentlemen, — the subject which wall most naturally attract our attention this evening, is that of the experiments which have been made by the apparatus now on the table before us. I had almost forgotten that at our last meeting we spoke of this instrument having been designed. It was not completed so soon as we expected ; and, although much time has been occupied in making experiments, the results are not quite so conclusive as could be desired ; but so far as they go are important — not only in respect to the problem we wish to solve, but, as bearing upon the pressure of the wind on the surfaces of planes. I will not now engage your time longer, but I will ask Mr. Wenham, under whose core, in conjunction with Mr. Browning, the experiments were carried out, to give a statement respecting the results. It is an instrument of a kind which I have .long desired, and it seems calculated to achieve what we require in this direction with greater accuracy than any other instru¬ ment I know. I call upon Mr. Wenham to explain the apparatus.
Mr. W f.nham expressed his regret at the absence of Mr. Browning, who had been associated writh them in these experiments. To make this instrument understood, he would explain how it acted as an ordinary anemometer, for ascertaining the direct force of the wind on a plane, when in a vertical direction to its surface. This consists mainly of a vertical steel spindle, supported on a hardened steel centre. Through an eye at the upper end of the spindle, a horizontal arm passes, and is secured by a small cross-pin, which allows the arm to vibrate like the beam of a balance. The long end of the arm carries the planes ; and the opposite short one has a sliding counter- weight, which is adjusted so as to exactly balance planes of different sizes at the long end of the arm. Each plane is clamped at the end of a tail rod, which is pivotted through the forked end of the arm, by a
OF GREAT BRITAIN.
7
vertical steel pin, as close to the plane as possible; the other end of the tail passes loosely through a vertical slot, slightly curved as a radius, from the balance centre of the arm. By this arrangement, the surface of the plane is always kept at right angles to the current, throughout the extent of its horizontal motion. A wooden shield is fixed close before the front of the arm, to protect this and the balance weight from the wind, so that the planes only may be exposed to its force. The action of the instrument, as a single anemometer only, or when the planes are set at right angles to the current of air, is obvious. The direct pressure is read off by the spring steel-yard, which is connected to the end of a lever from the vertical spindle, close to the base of the machine. In order to measure the vertical forces, the plapes are set at the requisite angles from a divided sector, whose centre coincides with 'the clamping screw at the back. The raising force due from the various inclines, was read off by the upright spring steel-yard. It was found almost impossible for one observer to read off the horizontal and vertical forces simultaneously during fluctuations, therefore the readings were noted by two persons at a given signal — even this was a matter of some difficulty. The arrangement would be far more useful and perfect as a scientific machine, if fitted with a piece of clockwork, moving a paper cylinder, on which the vertical and direct forces would be simul¬ taneously registered by separate pencils, describing two undulating lines, showing at a glance the relative forces ; the experimenter would then have nothing else to attend to, but to see that all other conditions were acting properly.*
The Chairman : I think the remarks by Mr. Wenham important, especially with regard to the effects produced on the planes at different inclinations. When the plane
* The tabular statement of the experiments referred to, were published in the Annual Report for 1871.
8
AETtONATTTICAT, SOCIETY
was placed vertical, the pressure of the blast of air was direct, and tended only to move the plane in a horizontal direction — being that of the dii'ection of the air itself — but when the plane was inclined, a part of the pressure was exortc d in raising the plate in a vertical direction, and a part only in exerting a horizontal pressure ; so that the latter was less than in the previous case. When the plane wac placed at an angle of 45°, the horizontal force and the vertical force were found to be identical, as mentioned in the manner described by Mr. Wenham. It was also found that whether the exposed surface was a circle, a square, or a parallelogram, providing the area was the same, the results were identical to the degree of accuracy to which the readings could be determined. Anyone who had not considered with care the nature of the pressure produced by the flow or rush of a fluid, elastic or incompressible, against a plane surface placed in its course, might imagine that the system of parallel forces was merely equivalent to a single resultant force acting at the centre of pressure, and capable of resolution according to the ordinary parallelogram law. But this of course is not the case, for the particles of the fluid which come in contact with the plane, have somehow or other to get out of the way, by gliding along the surface of the plane (as they cannot get through it), and this produces a complication in the neighbourhood of the surface of such a hind as cannot be theoretically predicted. One thing, however, is quite clear, and that is, that- the directions of all the small forces acting on the surface certainly are not parallel, and that we must therefore have recourse to experi¬ ment. Even the fact that when the inclination of the plane to the current (supposed moving horizontally) is 45°, the vertical and horizontal pressures are equal, is not by any means evident ; nor in fact can it be exactly true ; for supposing (to fix the ideas) that the upper part of the plane
OF GREAT BRITAIN-.
&
is bent over so as to point in a direction opposed to that in which the current is moving, and making an angle of 45° with it, then most of the particles of air in the vicinity of the plane will, in order to get out of the way, be moving downwards along its surface ; so that compounding this motion with that of the current, we should expect the horizontal force to be greater than the vertical. The experiments have shown that this difference is not appreci¬ able to the extent to which the instrument can measure it. The same qualification also must be understood to apply to these results, from which it would appear that the pressure was independent of the form of the surface. The velocity of the current in these experiments, was measured by a Lind’s Anemometer, an instrument that has never appeared to me to give very satisfactory results ; but still the only one available for the purpose. I regret that the apparatus is considered by Mr. Browning to be too delicate to be used in the open air, but I hope that this will not be always found to be the case. As I have said before, difficulties exist only to be overcome, and some day I trust, we may obtain a series of experiments, in which ordinary wind will replace the use of the artificial current. I see Mr. Brooke present, who helped us with the experiments, and he may be able to say something as to the results gained.
Mr. Brooke said it was not exactly mentioned, but the fact was notorious to everyone acquainted with mechanics, that in whatever position the plane was placed, the horizontal pressure may be resolved into two — one perpendicular to the plane, the other in the direction of the plane. It was clear that the resolved pressure acting in the direction of the plane was wholly effective in raising the plane. The resolution of the pressure into two, was well known to everyone acquainted with the principles of mechanics ; but it was to be understood that there were many other facts to be considered.
10
A.ERON ATTTICAIi SOCIETY
The simple geometrical consideration of the action of the pressure upon the plane, did not involve the necessity for the particles of air which had impinged upon the plane, getting out of' the way to enable other particles to impinge upon it. This led, in this experiment, to a result which might have been expected, but which it was important to ascertain. There were two rectangular planes of the same shape and area, and one was capable of being inclined lengthwise, in relation to the wind, and the other crosswise. Supposing the wind to be coming in a given direction (indicated as being towards the speaker) it was quite clear, with the plane inclined lengthwise, there would be less surface of the plane impinged upon, than there would be in the transverse direction (indicated on the instrument). The particles which impinged upon the former, must move along the plane, and had much more difficulty in getting out of the way, than particles which impinged on the plane in the latter position. This would show that the effective pressure of the wind at the same velocity was greater upon the one plane than upon the other. And, conversely, a revolving, or oscillating plane, moving in the former direction (indicated), would move with less force than in the latter direction (indicated). And here was an illustration connected with the wings of birds, particularly of those that had powerful flight — -where the wing was exceedingly long and narrow, it struck the wind in that direction (indicated). The experi¬ ment showed that from the same amount of surface, there would be greater effect upon the air by a long narrow wing, than by a short and broad one of the same area. That was one of the results that had been obtained by these experiments.
Mr. Wen ham : I partly neglected to show how this illustrates the flight of birds. You will find that the lifting power of the smallest angle is nearly five times that of the direct force. We were not able to try less angles. The smaller the angle of inclination, in regard to the current, the
OF CHEAT BRITAIN".
11
less the direct force ; and, comparatively, the lifting force is scarcely diminished. At 15 degrees, one force is nearly five times that of the other.
Mr. Harte asked if, in making those experiments, attempts were made to ascertain any pressure of the wind downwards.
Mr. Wenham: No! I omitted to mention that. A spirit level was laid across, so as to level the instrument. We had a trunk twelve feet long and eighteen inches square, to direct the current horizontally, and in a parallel course.
The Chairman : Certain conditions of current were tried by Lind’s Anemometer.
Mr. Haute : Did you notice, in making these experiments, where the centre of pressure came ?
Mr. Wenham : We were not able to ascertain very accu¬ rately. In all cases there was a tendency to lift the front edge.
Mr. Harte : Did you notice whether, according to the angle, the centre of pressure came forward?
Mr. Wenham : We found as the angle became more acute, the centre of pressure came nearer to the front edge.
Mr. Hall (of Acton) : Was the experiment made with a surface larger than one foot ?
The Chairman : We had one eighteen inches square.
Mr. Hall : A different result would, I think, be attained with two feet, from wh it was attained with one foot.
The Chairman : We have not spoken of two feet, because the shaft was scarcely large enough to give the even pressure required. We did not feel quite so certain with respect to large planer ; and, therefore, the experiments with them are not included in these records ; but I am ready to believe that the larger the planes, the larger the results. With areas of six inches, twelve inches, or two feet, the larger area, the larger are the relative results. I have had three or four anemometers together, and always found this to be the case.
12 AERONAUTICAL SOCIETY
Mr. Brooke : I rise to make an explanation. The 0 in the return ought to be 90. It ought to be 15, 20, 45. and 90.
Mr. F. W. Brearey (the Secretary) : If there is any gentleman here who could give us any advantage with regard to a fan-blower, we should be glad to avail ourselves of it. The area was so small, that we could not expose much surface.
The Chairman : But we ought to give our thanks to Mr. Penn, for the blower he lent to us, and for the use of his steam power. The entire work of the shop was stopped, during part of the time we occupied it. I should like to ask you to thank Mr. Penn, for the facilities he gave us on that occasion for making these experiments. (Applause.)
Thanks were accorded to Mr. Penn by acclamation.
The Chairman : I have now to introduce to your notice a gentleman who, I believe, has travelled more than 100,000 miles, and has visited New Zealand, California, and many other parts of the globe. Wherever he has been, he has watched as much as possible the flight of birds, and, as the result of his observations, he thinks it possible for man also to obtain flight. He knows New Zealand as well as he knows London, and he is now about to give us the benefit of some of his observations. We shall, I am sure, be glad to receive them. (Hear, hear.)
Mr. Head (the gentleman referred to) read a paper on
“ Flight."
“ Flight is performed by birds, insects, mammals, and to some degree by fish ; and long ago, in an old period of our world’s history, by dragons.*
“ Gliding down inclined planes is not true flight — because it must be very limited, and requires altitude in proportion
* Pterodactyls ♦
OF GREAT BRITAIN.
13
to length of horizontal distance. Still, animals possessed of the power of true flight, make great use of this advantage.
“ Flight is performed in straight lines, and curved lines ; and the curved lines may he of two kinds — the upward curved line of the flying-fish, and the downward curved line of the yellow-hammer and albatross. Bees, beetles, dragon¬ flies, cockchafers, and blue-flies fly straight — so do rooks, pigeons, ducks, and shags, and many other birds. Beetles, cockchafers, albatrosses, and ofttiraes hawks, ily on aero¬ planes, or under them rather, and are propelled in the desired direction, in the case of beetles and cockchafers, by their true wings blowing in the other.
“ How albatrosses fly I do not exactly know. Weight acts on a flying-fish directly he leaves the water, and also his inability to keep up his speed ; and so, by the law of con¬ tinuity it describes an elongated curve, with some slight contortions, caused by working its aeroplane fins.
“ A large flying-fish, about nine inches long, rose close to our weather-bow, and flew into a wave and rose again ; it then flew nearly to windward a long way, and three times gave itself a fresh impetus by sculling its tail in the top of a swell ; so that the fish was not lost to my view, though some distance off.
“ A dragon-fly has two pair of movable wings, and can dart about backwards as well as forwards, and it can also be quite still seemingly on the air. Bats fly in a most erratic course, but that only proves what command they have over their powers of flight, and is not a sign of weakness. So that besides the true manner, there are two distinct modes of flight — one, with an aeroplane, as the albatross, beetle, and hawk — and the other without, as sparrows, flies, and bats.
“ Flight, as it is performed by the non-aeroplane flyers, I leave, as being by far the most difficult to be achieved by us,
14
AERONAUTICAL SOCIETY
and as requiring not only an exact balance between the wings, but also an exact stroke equal to the weight of bird, and each wing equal to the other in direct line flight — the upstroke also being so regulated that the under-current of air is exactly equal to weight of bird — the down-stroke being the propelling blow, by blowing wind, or the air, in a direc¬ tion the more opposite to the line of flight the better ; as, if a fair blast blows ten pounds to the foot, and it be free in mid air, it would be driven in a contrary direction, with a force of ten pounds to the foot area of blast aperture, and if it presented five feet of area to atmospheric friction, it would be driven forwards at the rate of sixteen miles an hour.
“ Sky-rockets fly straight, only perpendicularly to still water — in any other direction they are drawn — by their weight, or, as it is called, the alteration of gravitation, more and more down, till they strike the earth ; but if they had the ears of a bat, or balancers like a fly, or a small fin aeroplane set to the exact angle, to suit their line of proposed flight, and the force employed, they would fly straight in any direction whatever — so long as the force was even and equal, and the wind did not vary ; and, then, a sky-rocket is a flying machine of the cylinder blast kind, and for the time carries its power with it — but, as it continuously gets lighter, of course it could not be set to go quite true. A steam-engine might be made on the same plan, with one end of the cylinder out, but it requires a great supply of steam, and could not be made to go far.
And now I come to consider aeroplane flight, and the best mode by which it can be attempted by man ; and — First, there must be three indispensable requisites, without which, it cannot be performed — weight; of which I need say no more, as that is easily obtained — but that without it, the machine might be any way up, and be carried about by any puff of wind. An aeroplane suspender, and a
OF GREAT BRITAIN.
13
force as a means to effect speed, or speed multiplied by depression of air, equals weight — for horizontal flight, and is so much greater for any angle upwards, to sixty degrees of altitude, above which an aeroplane could not be of much use. The great enigma is the necessary force to ensure a certain amount of speed to a plane surface, set to a certain angle, according to that speed, and with spread enough to drive down or press down air equal to the amount of weight of the whole machine and driver.
“ Can it be found? that is the question. And what is the amount of force requisite ?
“ Suppose that he is drawn up an inclined plane of any angle, and that the friction is nil.
“ On a level, it would require but a few pounds, except to start ; scarcely anything in fact. At the angle of thirty degrees, it would require about one-half of half a horse, or one quarter ; and twelve degrees, about half that, or one eighth. But we will reckon that a man and machine, at 200lbs., would require -100 x 16 ~ 6400 foot pounds per second — or rather more than } horse power, to raise per¬ pendicularly — that is, it would take one ordinary man and one-sixth of a man, to raise his own weight, and the balance of the 2001bs., sixteen feet, in the second of time, by any means at his disposal — without reckoning friction of atmosphere. To raise it twice as quick, would require four times the power, or nearly one-horse power perpendicularly — that is, at the rate of twenty-one miles an hour.
“ But we do not want to fly straight up, nor above an angle of thirty degrees ; which would not take quite half the powers of perpendicular ascent — excepting the friction which, on an aeroplane, you may count for nothing — (I am not now speaking of the friction of atmospheric resistance). And at an angle of ten degrees, about one man power would be sufficient to drive an aeroplane machine twenty miles an
16
AERONAUTICAL 80CIETT
hour ; which, I consider, to be very well, for it would not often be required to mount even at that grade — and once up, one could easily go on level.
“ I have not, however, taken into consideration the force required to drive the machine through the air.
“ To drive one foot through the wind or air, at the rate of fourteen miles an hour, requires one pound of force ; and, at the rate of twenty miles an hour, two-and-half pounds to the foot; and, reckoning the vertical area of the machine, man, and all at thirty feet, it would require one-fourteenth of a horse-power, or less than a half of a man to drive it through the air at the rate of twenty miles an hour.
“ And now the conclusion is, that a man could not raise himself on a machine, by his own exertions, at a greater angle than about eight degrees of grade, and at no much greater speed than twenty miles an hour — but even if that can be done, it would not be a bad beginning.
“Flying will become a business, and not every one could attain to it ; nor would it be desirable.
“ But flight by steam will be achieved yet An engine of 1-horse power could drive 1000 pounds up an incline of about 1 in 10, with proper appliances.
“ Now for the appliances ; calculating that a man — a gymnast at any rate — has power enough to sustain himself in horizontal flight an hour, and that he is the power obtained, and also the guiding will — having the weight and power— all we want is the aeroplane, and a means by which this power can exert itself in the air — in fact r machine, and one that can be kept in any proposed direction, and right way up.
“ Before considering that, I should like you to direct your attention to an arrow, or to the long rod of a sky-rocket, or the tail of a peacock, or bird of paradise, and to the long body of dragon-fly.
“ In the case of the arrow and skyrrocket, they are both kept in their places, or line of motion, by a light long drag
OF GREAT BRITAIN.
17
behind, as a steer-oar, and that is the best form for us to make use of at present, with weight forward.
“ Twenty miles an hour is a low speed, and is reckoned to an angle of eight degrees, but horizontal flight could be maintained to many times that speed ; and it entirely depends on the speed that can be obtained what size of aeroplane is required, and also the shape of it. The greater the spread the more air is passed over that has not been deflected downwards by the fore part of the aeroplane ; and so, for the same reason, a wide one is useless, that is long in the line of flight. So an aeroplane, or rather the pair of aero¬ plane wings, must be long and narrow — say twenty feet each, and three feet wide, or even less— about two and a half, or two — rather more than the proportion of the wings of, an albatross.
“ Also, a short bevel in the line of motion is easily regulated by an aeroplane lever, while a large square surface is only so regulated with great difficulty.
“ And now for the last consideration. How is the force to be applied ?
“ Whatever any one may say to the contrary all forward motion in flight is performed, or effected, by blowing in the other direction, and is the only way of doing it, as in swimming; and that can be done in many ways, as, a pair of bellows, a drum blast, or screw fans, or wing fans, or a fluke or common fa—
“ A whale can nearly lift himself out of the water by the accumulated momentum gained by a fluke fan in the water.
“Now a fan blast can be constructed to blow, say one pound to the inch — but say lOOlbs. to 1 foot, which gives a rate of 140 miles an hour to l foot, or about 25 miles an hour to 33 feet of exposed area of vertical surface.
“ But as the machine would have to run on wheels in order to gain momentum to start, the handiest mode for us
B
18
AERONAUTICAL SOCIETY
to make use of is to construct the pair of back blowing fan propellers of a size according to height and width of wheels, worked by a bevelled pinnace set to corresponding bevelled cog wheels inside the two driving wheels.
“ So the whole machine may be described as a simple velocipede, with the two driving wheels in front, and of rather large size, held up by a supporting canopy over the driver (which is not absolutely necessary), and two narrow long wing aeroplanes, slightly elevated, and bent like an unstrung bow, and kept in direction by a long steer oar with a broad horizontal plane and a narrow vertical one.
“ The steer oar to work on an universal joint, and the tiller to end in an oval ring, to encircle the aeronaut, allowing it also to work the small steering wheel aft.
“ I wish now, in conclusion, to say a word or two concerning the albatross, because I consider that it is the best flier in the world. He always lives in a half a gale, the great Southern Cyclone, and round and round the Pole he glides on his way. He has been caught seventeen feet from tip to tip, and I am sorry to say that I never heard what one weighed, or his measured area of spread of wings ; but I feel quite sure that as a pendulum takes but the slightest force to make it rise to the level from which it fell, so does the albatross fall from a height, and skim along and rise again to about a level with the point of departure, and so it flies on in, I think, parabolas downward, and with scarcely even a flap will keep with a ship travelling nearly three hundred miles a day, and coming and going for miles round all the time three thousand miles in a week.”
In the course of the reading, Mr. Spencer exhibited a miniature model of a boomerang, which he discharged from a spring, exhibiting the gyrations of the instrument in the air, and its return to the point of discharge.
On the conclusion of the paper,
07 GREAT BRITAIN.
19
Mr. Moy, advancing to the black board, explained by the use of diagrams, the adaptability of Mr. Scott Russell’s wave line to aerial machines. He said that he had studied ship-building in former years, and he thought that the knowledge so gained might be useful to aeronautical science. What they wanted in making the bow of a ship was to shunt the water off easily to the bend of the vessel. By using Scott Russell’s wave-line, they found that they did no more work than they wunted. If they tried the same principle of the wave line by that instrument, they would tind that whether the plane were long or short they got the same lifting power. Some gentlemen supposed that a cup surface would do better than that, but it would not. He should like to see an experiment tried on these planes if they could get a current of air blown upon them ; at the same time it would be better if they could get it tried outside. It would be better if they could get the instrument attached to a railway- train going at great speed, that might serve their purpose more effectually than blowers. When they came to flying machiucs they wanted to get very tine angles. The coarsest angle he would like would be 5 degrees. At these fine angles the wave line curve was almost flat ; but if they could accommodate those machines to the wave line it would be better than being quite flat. He mentioned this in order that those who were trying experiments might bear it in mind.
Mr. IIarte would like to ask Mr. Head, who had had such a large experience, if he had observed any difference between birds when flying through calm air and when in a storm.
Mr. Head said that it was scarcely ever calm in the habitat of the albatross.
The Chairman said that would lead to the inference that the stronger the wind the more easily the bird moved through the air, and that the action would be different in a state of calm from what it would be in a gale.
20
AERONAUTICAL SOCIETY
Mr, Head was not sure that the albatross could fly save in a gale.
Mr. Wenham could not agree with' the statement that a bird’s weight can act as an abutment, or a persistent force, in helping to sustain it in one direction against the wind, like the string of a kite ; or that the constant winds of the Southern Ocean are at all necessary to keep the albatross per¬ petually on the wing without effort. The bird is sustained by skimming over a vast body of air which may be in rapid movement against the earth, but with respect to its own condition is stationary. It may be a fifty-mile current, and if the bird make that speed in flight, in the direction from which the wind comes, it will make no progress relative to the ground, but in the opposite direction will speed on at the rate of 100 miles per hour ; yet its progress through the body of air will be identical in both cases, or fifty miles per hour ; and the conditions of flight are alike and the same as in still air. After the first abutment, spring, or momentum has been obtained, and the inertia from the earth expended, it ceases to exert any influence, and might be any distance off, or not there at all, as its presence does not affect the result. It was, therefore, a great mistake to suppose that the albatross was sustained in the air on account of currents prevailing in any one direction. The bird would exist in the same relation to the air as if it were in a calm, just as a balloon drifted along independently of the earth. It would be quite insensible of the current.
The Chairman : But the balloon goes with the wind — that I know to my cost (laughter). The bird goes against it.
Mr. Wenham : The bird with the wind will make 80 miles an hour; but, relatively, it would make the same, either one way or the other.
Mr. Head : I may make the remark that water in motion will carry big stones.
OF GREAT BRITAIN.
21
Mr. Wenham : There is a mistake. You throw a big stone into a rapid current, and it sinks to the bottom in a moment, and you will only see it bound and rebound as it is rolled along.
Mr. Head said that Canterbury Plains (New Zealand) were formed by boulders which had been brought down by the river. The whole of the West Coast of New Zealand was formed in the same way.
An Hon. Member : But those stones are at the bottom.
Mr. Moy : That is just the resistance of two elements. We might as well speak of a tile which was blown down in front of my house last January.
Mr. Stuart Harrison thought that with regard to that bird, the albatross, we had not got quite at the truth yet. The weight of the bird had, in his opinion, a great deal to do with the fact that it was sustained in the air. The weight of the bird served the same purpose as the string of a kite. Take the case of a balloon. The balloon had no gravity, no tendency to fall ; but it simply floated as a piece of wood on water. Now take the case of the albatross. The wind impinged against the wing of the albatross, and, supposing that the bird had no gravity whatever, it was clear that the force of the wind on its wing would drive it more and more in one direction. The bird would continually rise ; but the fact that the bird had gravity, enabled it to fly in another direction, at a fixed position, relatively to the earth. At that position the bird would remain over a fixed spot, with out¬ stretched wing, because the current of air and the tendency of the bird to fall would counterbalance the elements of motion. Change of position would give that motion which the reader of the paper had so graphically described as a movement of the wing.
Major Robertson had seen many albatrosses fly, and quite agreed with the observations just made. With the
22
AERONAUTICAL SOCIETY
albatross, it was easier to fly in a gale of wind than a calm, because of its very great weight.
Mr. G. J. M. Hardingham was not quite satisfied about the albatross. Illustrating his remarks by lines and curves on the black board, he explained the action of the force of the wind, and the counter-balancing power of gravity as affecting the flight of the bird. But it was a mistake to investigate this albatross question so much. The action of a crow’s wing would much more forcibly illustrate the action of a bird in flight. Instead of looking at extraordinary flyers, such as the albatross, they should take a simple flyer, and if they could explain that they could get at the other. A great deal of the different kinds of flight could be explained by the angular set of the wing — (explained on the board). Judging from his observations of the effect of the down strokes of the wing in sustaining a bird, he worked it out, and found that for a machine to lift one man the horse-power came to about twenty horse-power ; so that the chief objection was, they would have to get a very strong man indeed to work a machine for the sake of lifting himself. The fact was, that the forward resistance was a mere bagatelle compared with overcoming the gravity. The great thing was, therefore, to overcome the gravity.
Mr. Hall remarked that birds of the crow kind very rarely soared about, or sailed with the wing in a motionless condition, as the albatross and birds of larger powers of flight. These larger birds brought their weight greatly into play to enable them to hold their own against opposing currents of wind. He believed, therefore, that wdien flight by human beings was brought into operation it would be by bringing the weight of the machine into play as a balancing power. It was weight that enabled the condor to fly many miles in a few minutes, without any motion of his wing, in the elevated region of the Andes. This could not be
OF GREAT BRITAIN.
23
obtained by any other means than weight. He had been brought to this view some years ago by observing gulls flying on the seashore. He noticed that they kept themselves suspended simply by bringing their weight into a state of equilibrium, and always keeping their head to the wind. He had formed many models upon this relation of weight and equilibrium. First, he formed them on the plan which Mr. Moy deprecated — the cup shape — but he found it better afterwards to adopt the wave-line stem for his embryonic flights. He was convinced that the wave-line was the right principle, and he was trying to bring it into action. His great difficulty was to get an opposing current of air strong enough to get the machine away from the earth. Dr. Pettigrew, in the current number of the Natural Science Review , had adopted the same view. He would ask the gentleman who read the paper, and who spoke of “ flittering flight of bats,” whether he had not seen large bats fly almost like the albatross, in a straight line.
Mr. Head : I have heard of them, but I never saw them.
Mr. Brooke thought there could be no doubt that a bird’s wing did assume the wave-line in flight.
Mr. Arthur M. Saunders asked whether the wave-line was intended to increase or diminish the resistance. It appeared to him that with an aeroplane the object was to increase the resistance so as to give more lifting power.
Mr. Moy remarked that if they wanted to send a ship rapidly through the water they would adopt the wave-line ; but if they wanted her to go down, they would adopt another shape. The wave-line got rid of the resistance forward.
An Hon. Member suggested that some experiments should be made on the wave-line principle.
The Chairman : That will be another class of experiments. The great thing was to connect pressure with velocity.
Mr. Hardingham would like to know how velocity was measured.
24
AERONAUTICAL SOCIETY
The Chairman: It was not measured. The experiment was merely by pressure on the surface. We have no idea at the present moment of the connection of pressure with velocity : it probably varies as the square. But I did hope we should have been able to get some results to-day,
Mr. Hakdingham remarked that resistance was according to the sine. It was nearly the square of the siue.
The Chairman : There is one duty we have to perform. It is fortunate that this gentleman has been travelling in those regions so far and so long, and it is still more fortunate that he has come to give us, in the simplest language he has been able to use, the results of his observations ; and I am sure you will thank him for what he has done (hear, hear). He has not only seen, but has reflected ; and has put his thoughts into shape, and given them to us. I therefore ask you to thank him for his paper.
Carried by acclamation.
Mr. Head acknowledged the compliment.
The Chairman remarked that he had still a paper, written by Mr. Gosling, C.E., of Bombay, but it would be for the meeting to say whether at that late hour they would hear it, or would reserve it for a future meeting.
On the question being put, the latter course was approved, and, after passing a vote of thanks to the Chairman for presiding, the meeting adjourned.
OT GREAT BRITAIN'.
25
The paper published in the last Annual Report, con¬ taining extracts from “ Lectures on the Phenomena of Flight in the Animal Kingdom by M. Marey, of the College of France, was translated and contributed to the Society by Mr. T. J. Bennett.
A more detailed translation has been called for, in compliance with which we must almost absorb, if not exceed, the space allotted to the Annual Report for 1872 : —
The Movements of the Wino of Insects.
* * * * * *
We have begun to study the motions of the wings, and the first question which presents itself is the frequency of these motions. On this point direct observation is of little assistance ; the acoustic method, which consists in determining the frequency of the strokes of the wing by the pitch of the buzzing of the insect is more efficient, but we have seen that even the principle of this method lias been contested, and that its application presents difficulties. The graphic method remains to be considered. This method consists in making the wings themselves record the strokes which they execute. When an insect is held in captivity by force which it cannot overcome, after trial it ceases a useless resistance ; it resigns itself and abstains from all efforts to escape, its wings remain immovable, and in this way the observer who hopes to study their motions finds himself disappointed. But there are different methods of awakening the insect to its original activity ; it is sometimes sufficient to pinch the antennae lightly ; this irritation of a very sensitive organ succeeds with the Macrogtossa. Among the wasps the end may be attained by titillating the feet, or by holding them all together with a pair of forceps, and then releasing them suddenly, except one, by which the animal is held. The captive supposes that it is at liberty, and makes an effort at flight, which lasts about thirty seconds, or long enough to be observed. There is, however, another difficulty. The captive insect, when willing, cannot fly like an insect at liberty, because the external conditions are not the same. It experiences a greater resistance in proportion to the traction which it exerts upon the bond which holds it ; to a free insect the relation is such as a boat held by an obstruction bears to one sailing freely, or as a horse which drags a load to one relieved from harness. This resistance modifies its behaviour considerably, and obliges us to distinguish between the two different conditions of free flight and flight in captivity. It is indispens¬ able to establish these distinctions, in order to appreciate at their true value the results to which we are conducted by the graphic as well as the other methods which we may employ.
The apparatus on which the wings record their motions is the ordinary registering apparatus, consisting of a metal cylinder, covered with smoked paper, to which a uniform rate of motion is imparted by clockwork. Let as suppose that, instead of the motions of the wings,
26
A EROW AjmCAL SOCIETY
we would simply register the oscillations of a vibrating-rod. For this purpose the extremity of the rod is furnished with a little style, which touches the blackened paper with its point, and, as the different parts of the movable cylinder pass successively before the point, the soot is detached from the places which it touches, and a trace produced. If the rod is not in vibration, it makes a long white rectilinear trace without sinuosities, a straight line which, rolled upon the cylinder, constitutes a circumference. If it is in vibratory motion, its trajectory will be a curved line, of which the sinuosities indicate all the circumstances of the motion, its phases of elevation, its depressions — in a word, all its movements — and consequently all the oscillations which the vibrating rod executes in space will be faithfully reproduced on the paper. If we would ascertain the frequency of the oscillations, it is sufficient to know the rate at which the cylinder revolves. Ordinarily a tuning-fork is employed, of which the number of vibrations is previously known, as, for example, one hundred vibrations per second. This is made to write its vibrations upon the registering cylinder below the line traced by the vibrating rod, of which the number of vibrations are desired. The comparison of the two tracings shows at once the number of the motions of the tuning-fork back and forth, that is to say how many hundredths of a second correspond to one oscillation of the rod ; the number of motions of the vibrating body during a given time is thus known with great exactness.
It is not, however, as easy to obtain the tracing from the wing of an insect as from a vibrating rod, and this for several reasons. In the first place, it is very difficult to fix at the extremity of the wing a writing style ; however light it may be, the rapidity of the motion to which it is submitted is sufficient in most cases to throw it off. If, however, after many trials and much precaution we are able to retain it in its place, a permanent cause of perturbation still exists from its very presence. Under the influence of this incumbrance the extent and frequency of the strokes of the wing are evidently diminished. It is easy to convince ourselves of this, by taking a Macroglossa and fixing it in the manner which we have previously described, that is, immovably between two strips of cork, by means of a pin. Looking down upon it, we perceive the extreme limits traversed by the wing above and below, which we have called the dead-points. If some substance is applied to the surface of the wing, we see by the effect of this burden, in diminish¬ ing the play of the organ, the two limits of oscillation approach one another, and the extreme upper position, which just now was almost vertical, inclines towards the horizontal. We may finally remark that it is only at the cost of considerable chafing against the surface of the moving cylinder that we can obtain a complete tracing of the movement of the wing. The wing cannot touch the cylinder, except during a very short instant of its stroke ; that is, the instant when the wing reaches precisely the distance from the body of the animal to the cylindrical surface. The spherical figure which the margin of the wing describes in space, cannot have more than one point in common with the blackened cylinder. We can therefore only obtain, as the whole impression, a series of points at more or less regular intervals ; and, if a more
OF GREAT BRITAIN.
27
prolonged contact is desired, it can only be by curving the wing and folding it upon itself, and consequently the natural curve which the organisation of the insect obliges it to traverse will be falsified and altered. In any case the friction against the blackened surface will retard the motion, and although the retardation which it causes may be neglected when it is opposed to bodies of large size, such as a tuning- fork or a vibrating-rod, it cannot be when the vibrating object is the delicate membrane which constitutes the wing of an insect. Again, the friction, although exceedingly small, is found fully comparable with the forces which come in play in the motion of the wing, and its intervention notably alters the action of the latter. Experiment has confirmed these views. In one case an insect executing the motions of flight, and rubbing its wings somewhat roughly against the paper, furnished 240 movements per second ; by diminishing more and more the contact of the wing with the cylinder, there have been obtained 282, 305, and 321. If, therefore, we would have a faithful representation, it is necessary to renounce the idea of obtaining those beautiful, regular, and continuous lines which are produced by the tuning-fork or vibrating-rod, and content ourselves with interrupted lines, half-strokes, represented by fragments, or even only isolated dots, the periodical return in these incomplete markings of definite forms permits us to infer the repetition of similar oscillations, and hence to determine their frequency. The operation is as follows : with a delicate pair of forceps we hold the insect by the lower portion of its abdomen, in such a position that one of its wings at each movement shall lightly touch the blackened paper. Each of these touches takes off a portion of the soot which covers the paper, and, as the cylinder turns, new points incessantly present themselves to the contact of the wing. A figure is thus obtained formed of a series of points or short strokes of perfect regularity if the insect has been maintained in a fixed position.
We have obtained a large number of these tracings in which the wing has only touched the surface of the registering cylinder, and has left only a point as a mark in each of its vibrations. I exhibit a number of these, and trust as soon as the return of Spring permits us to procure insects to show you the experiments by which these tracings have been produced. Those which you are now examining have enabled me to determine the frequency of the strokes of the wings of the following insects : —
Strokes per Second.
Common fly .. ... ... ... 330
Humble-bee ... ... ... ... 240
Honey-bee ... ... .. ... 190
Wasp ... ... ... ... ... 110
Sphinx moth ( M acroglog&a ) ... ... 72
Dragon fly ( Libellula ) ... ... ... 28
Cabbage butterfly ... ... ... 9
Certain authors have estimated this number of vibrations by the acoustic method, but there is a notable discrepancy between the above figures and those which they have deduced from the pitch of the sound that these insects produce in flying. In the case of the common fly,
28
AERONAUTICAL SOCIETY
T. Lacordaire has computed the number of the vibrations of its wings at 600 per second, that is to say, twice as many as our figures exhibit. Has there not been a misunderstanding here, as is frequently the case, in the use of the word “ vibration ? ” Some persons wrongly consider the raising and depressing of the wing as two vibrations, and reserve the term of “simple vibrations” for one or the other of these isolated motions. On the contrary, if we follow the usage most generally adopted, the two motions together, by which the body is again in its original position, should be considered as a single vibration.
The previous observations which we have made on free flight, and on flight under restraint, somewhat curtail the range which we are tempted to accord to these numbers. The animal, according as it desires to move with a greater or less rapidity, can change, at will, not only the extent of its wing-strokes, but also, to a certain extent, their frequency. Fatigue may exercise an analagous influence to that of the will ; after very rapid motions, the exhausted animal diminishes the number of its strokes, which sometimes falls to a fourth or a fifth of its normal value. It continues to relax them more and more until a period of repose and reparation permits it to resume its usual flight ; neverthe¬ less, the examination of these numbers suggests some general considerations. We have reason to think that each of the muscular contractions which determine the drawing down of the wind is the result of a single impulse ( Zuckung of the Germans), although in man contraction is due to successive impulses, which are merged in one another when they are produced more frequently than 30 times in a second. Among insects the limit of fusion of impulses is infinitely more remote, and ends with leaving the wing immovable, in a sort of permanent tetanic contraction. It is easy to assure ourselves of this by means of living insects, or better, by means of the artificial insect which I have constructed. When the impulses become too rapid, their extent diminishes ; at this moment they no longer serve for the propulsion of the animal, whose wings appear quite immovable or merely agitated by a fight tremor. Nevertheless, the number of muscular waves which the fibres of insects will admit without inter¬ mingling, a number which in the fly amounts to 300 per second, forms a physiological fact very interesting to note. Among other animals the limit is not so remote ; among birds fusion is produced after 75 impulses ; among mammals after 30, and among reptifia after only 4. These differences correspond, in virtue of the relations which I have long since explained to you, to analagous differences in the rapidity with which the elementary impulse traverses the muscular fibre of these different animals. The muscular fibre of the insect will then be characterised, physiologically, by the property which it possesses of furnishing a considerable number of distinct impulses, as well as it is anatomically characterized by its relative size and its striation.
The graphic process which enables us to judge of the frequency of the strokes, also permits us to show the perfect synchronism of the play of the wings. For this purpose it is necessary to choose an insect of which the amplitude of the wing-vibrations is large, so that in their moment of greatest elevation they may nearly meet above the dorsal region of the animal. If the insect is placed near enough to the regis-
OF GREAT BRITAIN.
29
tering cylinder, the dorsal region turned toward the blackened surface, it is clear that at the moment when the wings approach each other they will leave their traces on the paper, thus describing a series of loops and curves, of which the perfect correspondence proves the synchronism of the motions from which they originate.
Fig. 3.
Simultaneous tracings of the wings of ,a wasp in short flight. The perfect synchronism of the two wings will he observed.
Furthermore, we can convince ourselves that a sort of necessary connection exists between the motions of the two wings. If we throw an insect violently upon the ground, so that it is stunned and can no longer execute voluntary . motions, we observe that, by producing motions in one of the wings, the other follows, to a certain extent, the injuries inflicted on its fellow. If one of the wings of an insect is depressed, the other also bends down ; if one be raised, the other elevates itself. Certain species, especially the wasp, lend themselves very readily to this experiment. According to Chabrier, the author of an extensive work on the mechanism of the flight of insects, synchronism cannot fail to exist. This author considers the depression of the wing as the only effective portion of the stroke ; its elevation is a passive phenomenon due to the action of physical forces. In fact, after the depression each dorsal arc of the thorax is deflected like a bent bow, and when the muscular contraction ceases the bow springs back in virtue of its elasticity, and the wing is raised. Now, if the pressure did not act simultaneously on the two extremities of the bow, it could not be flexed as it is, and the mechanism, which we suppose, would be impossible. The reality of this synchronism is, then, a strong proof in favour of this manner of understanding the motion of the wing.
After having determined, in a general manner, the frequency of the vibrations of the wing,, we seek to know the variation produced in the number of these vibrations by agents capable of influencing the activity of the animal. In the first rank of such agents must be placed heat and cold. We know that warm dry weather is essential to insects, especially coleoptera, to enable them to fly well ; special observation has confirmed this fact. We are able to state that, within certain limits, the frequency of the strokes is augmented with an increase of the temperature, and that they become slower under a gradual increase of cold.
Form of the Motions of the Wings.
After having studied the frequency of the vibrations of the wings, it is necessary to study their form. For the end which we desire to obtain — that is, to arrive at a theory of the flight of insects — the most important element to comprehend is that which we now proceed to investigate, namely, the form of the trajectory which the wing describes in space, instead of the rapidity with which this trajectory
30
AERONAUTICAL SOCIETY
is described. In order to arrive at this determination we shall have recourse to two processes, which will reciprocally correct each other — the optic method, and the ordinary graphic method.
Optic determination of the movements of the wi/ng.— When a brilliant body moves with rapidity, it leaves upon the retina a kind of luminous train, which acquaints us with the trajectory through which the body has passed. Children sometimes amuse themselves' in producing the most varied figures by brandishing in the air a stick having one end on fire. It is on this principle that the apparatus, known in physics under the name of Wheatstone's calidrophone, is founded. This is a rod, fastened upright on a heavy foot, to which complex vibrations may be given, and to the ends of which a brilliant metallic bead has been affixed. If the rod is put into vibration the brilliant bead describes in space luminous figures, which vary with the different combinations of the vibratory motions. If a brilliant spangle can be attached to the extremity of the wing of an insect, this spangle, traversing without cessation the same points in space, leaves a continuous luminous figure exempt from the imperfection which is caused by friction in the case of the graphic cylinder. The extremity of an insect’s wing can thus be rendered brilliant without mutilating it in any way ; it is sufficient to place upon it a drop of varnish, to which a small piece of gold-leaf is applied. The varnish dries so rapidly that the insect cannot throw off this little reflector of light, and nothing more is necessary than to hold the animal in a fixed position to observe the play of light upon the small brilliant surface. Under these conditions the bee and the wasp furnish a well-marked “ figure of eight.”
Fig. 4.
Aspect of a was]), the extremity of whose primary wings has been gilded. The animal is supposed to be placed in a ray of light.
OF GREAT BRITAIN.
31
The figures of eight are more or less widened or compressed, according to circumstances. Sometimes the point of the wing seems to move almost in one plane. In the dragon-fly ( Libelluln) a figure of eight is also observed, but much more elongated ; the loops are narrow and laterally compressed. With the Macroylossa yalium it sometimes seems as if the preceding form had disappeared, and is replaced by a sort of ellipse. However, in examining it closely, it is soon perceived that this ellipse is surmounted by a little loop, very slightly developed relatively to the curve which supports it. It seems that one of the loops is enlarged at the expense of the other, but this last has not entirely disappeared, and the vestige what remains testifies to the persistence of the figure of eight which is encountered in most other cases, and which may serve as the general type.
Changes of the plane of the winy.— The luminous figure which the gilded wing of an insect gives in its motions also shows that, during the alternate motions of flight, the plane of the wing changes its position in relation to the axis of the body of the insect. During the period of elevation the upper face of the wing is directed backward, while it turns a little forward during its descent. In fact, if we gild a large extent of the upper face of the wing of a wasp, taking care that the gilding shall be limited to this face, it is seen that the insect, placed in a ray of light, gives the figure of eight with a very unequal intensity on the two sides of the image, as is seen in the preceding figure. It is evident that the cause of this phenomenon is found in a change of the plane of the wing, a change in consequence of which the angle of incidence of the solar rays, while favourable during the ascent of the wing, is unfavourable during the descent. If the animal is turned so that the luminous figure is observed inversely, the figure of eight presents, in an inverse position, the striking inequality of its two halves, catching the light in a portion which was just before without it, and losing it where it had previously shone. We further find, in the employment of the graphic method, new proofs of the changes of plane in the wings of insects during flight. This change of plane is of great importance, for in this rests, as we shall see, the immediate cause of the propulsion of the body of the animal by the application of the motive force.
Method of contact. — Does the extremity of the wing really describe this double loop which we perceive, or is this form the result of an optical illusion — a play of flight ? Though such an objection is hardly probable, it is necessary to refute it. To assure myself more entirely of the reality of the displacement of the wing than the optic method rendered perceptible, I have introduced, while the w'ing was in motion, the extremity of a little bodkin into the interior of the loops of the figure of eight, and J have established that in the interior of these curves free spaces really exist of a funnel shape, in which the bodkin penetrated without encountering the wing, while if I attempted to touch the intersection where the lines cross, the wing immediately struck against the bodkin, and flight was interrupted. Still greater precision can be brought to bear on the appreciation of these motions, and, knowing that the wing describes a double loop, it may also be
32
-iEROK ATTIC AL SOCIETY
known in what manner it transverses the branches. It is sufficient to bring near to the wing in motion a leaf of paper blackened on both Rides ; the wing, in pursuing its course, strikes against one of the sides of the paper, and the trace which it leaves testifies to the manner in which the motion is accomplished.
Graphic method. — This method is not applicable to our problem without important modifications. We have just seen that it is difficult to obtain tracings of any extent, because the wing cannot remain long in contact with the blackened cylinder, which it leaves and approaches successively. Under these special conditions it is necessary to have recourse to an artifice, and since it is impossible to obtain a satisfactory trace at a single stroke, we rnould try to divide the difficulty and separate the operation into several periods. The preceding experiments simplify the interpretation of the tracings very much, and we can reconstruct the, figures which the optic method has indicated from the slender elements which they afford. I have considered in the complete course of the wing of an insect, such as is represented in Fig. 4, three distinct zones, of which I have obtained the tracings separately ; an inferior zone, corresponding to the lower portion of the figure of eight ; a median zone ; and a superior zone corresponding to the middle and upper parts of this figure. Bringing together the tracings obtained in these three zones, I have been able to reconstruct the entire curve. In registering the tracings of the median zone, figures much resembling each other are obtained, presenting the two crossed lines shown in Fig. 5.
Fig. 5.
Trace of the median course of the wing of the Macroylossa galium (Bedstraw
sp’nynx moth).
The multiple tracings of the figure are formed by the fringed extremity of the wing, which presents many small points. The upper portion is in the form of a loop, as well as the part which corresponds to the lower course of the wing, and these three parts successively obtained give, when united together, the complete representation of a figure of eight, such as is obtained in acoustics in registering by Koenig’s method the vibrations of a Wheatstone’s octave rod ; that is, a rod which vibrates twice transversely for each longitudinal vibration. The slower motion of the cylinder produces the condensation of the end of the tracing.
OP GREAT BRITAIN.
33
Pig. 6.
Trace of a Wheatstone’s octave rod.
The experiments can also be varied by obtaining, not the tracing of the point of the wing, but that of the anterior border of this membrane striking laterally against the cylinder. It is clear that in describing the upper loop, this edge will approach the cylinder, then deviating, in a similar manner it will describe the lower loop, so that in its complete course it will rub twice against the blackened surface, and leave two white traces separated by an interval. This is observed in Tig. 7.
9 ' v
i . ,
- . > ■ - v - t
v v ; P - ' : ; ‘
. if
f ' ' ' ' | , ) j | ! 1 >
>
V
This figure shows from the tracing of the wing of a wasp the upper loop and the whole extent of one of the branches of the figure of eight. The median portion of this branch is only dotted on account of the feeble friction of the wing. We may, therefore, be permitted to con¬ clude that if the trace of an insect’s wing could be obtained entire at one operation, the same figure would be presented which we have seen described in space by the gilded spot on the wing of the wasp, namely, a figure of eight, which our ingenious acoustician, Kcenig, was the first to obtain with a spiral Wheatstone’s rod, making two horizontal to one •vertical oscillation.
It now appears to me sufficiently established tnat in the more extended motions of flight the wings of insects describe a figure of eight in space. Furthermore, that the luminous figure which a speck of gold on a wing presents in its motions, has shown us that the periods of ascent and descent of the wing are accompanied by a change of plane in that organ. It is this fact which will shortly enable us to explain the mechanism of flight in insects.
C
34
AERONAUTICAL SOCIETY
Mechanism of the Flight of Insects — How they Propel
Themselves.
The preceding lessons have been devoted to the study of the frequency and the form of the strokes of the wings of insects. You have seen that the frequency varied in different species, and in passing from the butterfly, for example, to the house fly, or the gnat, the variations may be considerable. The flight of the butterfly is slow, the strokes of its wings succeed each other at considerable intervals, propelling it by bounds and jerks, and producing ap irregular and capricious flight. The gnat darts with rapidity straight at its object, emitting along its path a clear, sharp, strident sound. Between these two extremes we find all intermediate stages. Furthermore, the same insect, under different conditions, varies the rapidity of its motions within extensive limits ; when free from all restraint its movements are rapid and precipitous, but when captured they are immediately relaxed, and although the frequency of the movements of the wing varies, the form of the motion does not change. It is in all cases the same, always a double loop, a figure of eight. Whether this figure be more or less apparent, whether its branches be more or less equal, matters little ; it exists, and an attentive examination does not fail to reveal it.
Before drawing from this fact the conclusions which it warrants ; before extracting from it the solution of the problem with which we are occupied — that is to say, the mechanism of flight— let us rapidly review the history of the question, and see how far previous authors have advanced in its solution. Without going further back, we find in the work of Borelli a chapter devoted to this subject, in which lie considers the force which the bird or insect must employ to sustain or move itself in space. He estimates that this force is enormous ; that it is, in the case of the bird, more than ten thousand times greater than the weight of its body. We still find this exaggeration in recent works. The academician, Navier, falls into an analogous error, and after him M. Babinet accords, in his turn, a power to the inhabitants of the air far superior to that with which they are gifted by nature. However, by the side of these errors we find a great number of correct ideas, since confirmed by observation. Borelli knew that the principal motion of the wings was an elevation and depression, executed in a vertical plane, and he asked himself how it was possible that this motion, which, it seemed to him, could only serve to elevate the animal or to depress it, should nevertheless contribute to onward motion. For this, it was necessary that the vertical force should be changed into a horizontal force. Example" of t’ is transformation are frequent. If a wind blowing horizontally strikes against a flat board inclined forward at an angle of, say, forty-five degrees with the horizon, the action of the wind will tend to throw it backward and upward ; or, if the board is moving forward with a momentum, it will tend to elevate it. We have here an illustration of a well-known principle of mechanics — the resolution of a single force by an inclined plane into two forces — which gives in part an explanation of the flight of insects and of water birds. But insects have four wings instead of two. Is the office of these four organs the
OF GREAT BRITAIN.
35
same ; and if not, in what do they differ ? Borelli does not treat of this question. It is discussed, however, in a particular case, by an anonymous author, who has left us an interesting manuscript on the habits of bees. This work, intended to complete and to correct the work of Reaumur, came from the Condamine Library, and belongs to M. Hamet. The author has observed bees at the moment when they hum at the mouth of the hive, trying to enter it and deposit their treasure. In examining the play of light on their trembling wings, he thinks that he saw the upper pair alone alternately raised and depressed, while the lower pair were animated only with a. feeble horizontal motion. Here the question seems to have been abandoned, although the interest with which it is now regarded is far from inconsiderable. Beside the interest which it offers from the purely scientific point of view, in the mechanism of a function #as widely employed as aerial locomotion, still another interest is attached to this study. The insect and the bird realize one of the oldest and most unsuccessful aspirations of the ambition of man. A 11 space belongs to them ; they go and come in the aerial ocean, while he is chained by his weight to the earth. Man has sought by various methods to escape from this confinement. The knowledge of the processes by which Nature attains the end to which he aspires, would perhaps have spared him many fruitless attempts and loss of much time and great waste of invention. In 1823 a work appeared in which this question of aerial locomotion is treated ex professo, and no longer in an incidental manner. The author, the Chevalier de Chabrier, studied the conditions of mobility of the wing, and arrived at the solution of an important question : how muscular action is transmitted to this movable organ. Is it directly, or by some intervention 1 The muscle, responds Chabrier, is not directly attached to the wing ; it acts upon the arch of the hack. When it contracts, the curvature of this arch is augmented ; when it relaxes, the back returns to its original curve, like an unbent bow. In the motion of the wing, therefore, there is only one active period, the moment of depression ; the period of elevation is passive. Elasticity, therefore, plays an important part in this function. Here, as in all mechanical organs, it absorbs and then gives out power ; it regulates speed and produces continuity of motion.
But Chabrier was soon carried away by an exaggeration similar to that of Borelli and of Navier, though in a contrary direction. According to him, an insect needed an insignificant force for its propulsion in space. No effort was necessary to sustain it in the atmosphere ; the animal floated there like an inflated balloon. In order to fly it filled its multitude of respiratory canals with air, and this, becoming heated, raised the animal as it elevates a hot-air balloon. It is not necessary to say that this conception of an aerostatic insect is an error. Without doubt an insect, before attempting a flight, lays in a quantity of air by a sudden respiration, but this provision of air contributes only an insignificant part toward the end which Chabrier assigned it.
The greater portion serves to prepare the organs of flight for the operation of their function. Jurine, of Geneva, in particular has
36
AKRON ATTIC AX. SOCIETY
shown that the nervures of the wing membranes are small tubes which only acquire the rigidity and extension necessary to flight by inflation with air. We must refer to another contemporary, Strauss Durckeim, to find the elements of the theory to which my observations have conducted me. In his book on the Theology of Nature, a vast chaos of ingenious ideas, in which some profound, among many puerile, thoughts are to be found, there are many facts essential to the solution of our problem. Strauss Durckeim has conceived the ideal type of the insect- wing, the diagrammatic wing ; that is to say, has reduced the organ to its essential parts. It consists of a rigid nervation or frame-work in front, a flexible web behind ; this is all the apparatus. An apparatus thus constituted possesses the essential requisites for flight ; otherwise constituted it will not serve this purpose, as is the case with the false- wing of the Phryganidce, which has its principal nervation behind. It is enough that such a structure should be made to rise and fall successively : the forward border being rigid and the other flexible, it naturally disposes itself in an inclined position, receiving the reaction of the air obliquely, and thus transforms a part of the vertical impulse into a horizontal force. The two parts of the wing above mentioned are both indispensable in the same degree their respective offices complement each other in producing a single result. Ingenious experiments, due to M. Girard, throw light upon these facts. Destroy the anterior nervation, without removing the thin membrane, and the insect cannot fly ; destroy the flexibility of the membrane by covering it with gum, and flight also becomes impossible. Here we cannot urge the objection that the superincumbent matter interferes by its weight like a burden which weighs down the animal ; for, following out the experiment, we see that as soon as the coating becomes dry, small fissures are produced, flexibility reappears, and with it the possibility of flight returns. These observations assist us in comprehending the part which the anterior portion of the wings of the Phryganidce play ; which constitute the analogue of the stiff nervure, while the hinder wings represent the flexible membrane. The two wings of an insect thus complement each other.
I shall not further prolong this retrospect. I have limited it to the essential ideas entertained by our predecessors, and to those which will serve us in the future. The preceding experiments, joined to those which you have seen performed under your own eyes, seem to me to establish the following facts, namely : the motions executed by an insect during flight are- limited to an elevation and a depression of the wings. It is true that other motions take place in the wings of insects. They are seen to move backward, and in repose to extend parallel to the axis of the body. We also see insects moving their wings backward and forward in preparation for flight. But these motions are not directly connected with aerial locomotion. The dragon-fly ( Libelhda ), which propels itself so rapidly, exhibits none of these lateral movements ; its wings move exclusively in a vertical plane as if they turned on a hinge. But we have seen, in the optic method, that the course of the wing in space can be followed by gilding its extremity, and placing it in a ray of sunlight. Now this arrangement furnishes us with a figure of eight,
OR GREAT BRITAIN.
37
and we further know that during each complete vibration the wing changes its inclination twice. These movements are not controlled directly by the muscles. They are the mechanical effects of the resistance of the air acting alternately on the upper and lower surfaces of the wing in its alternate movements. When the wing leaves the upper limit of its position it inclines neither to one side nor to the other, its plane being parallel to the length of the animal. But when the impulse of the air is exercised, or as soon as the wing begins to be depressed, the rigid portion, the anterior nervation resists flexure while the flexible membrane which follows it gives way ; drawn down by the nervation which lowers it, elevated by the air which uplifts it, this membrane takes an intermediate position ; it inclines about 45 degrees, more or less, according to circumstances. The wing continues its downward motion thus inclined toward the horizon. Thus the reaction of the air, which combines its effect and acts perpendicularly upon the surface which it strikes, can be decomposed into two forces, a vertical and a horizontal force ; one serving to elevate and the second to propel the animal. After this first period the wing membrane will have arrived at the end of its course ; the direction of its motion is changed, its action is reversed. A moment of repose, infinitely short, separates these two phases during which the wing resumes its normal position parallel to the axis of the body. The nervure draws it up again, the air resists as before, and from this conflict results a position between the horizontal and the vertical — an inclination of 45 degrees. This second period contributes as did the first, to locomotion. How remarkable is the simplicity of apparatus by which the desired end is attained !
The horizontal force which is generated by the inclination of the plane of the wing is transmitted to the body of the animal and helps to push it forward. But as the body of the insect does not instantaneously take up the motion which is imparted to it, a part of this force is expended in curving the nervure of the wing which, at the same time that it is lowered, is pushed forward. Here is an artifical wing of large size constructed in accordance with the type which we have described ; an anterior nervation represented by a stiff rod, with a membrane behind formed of paper pasted upon its edge. Try to strike down an object immediately before you, and you will not succeed. If you strike at an object before you with a downward blow the wing will be resisted by the air, and it will deviate greatly from the point at which you are aiming. From this deviating motion of the wing from the change of plane which it effects, the looped figure which it describes evidently results. It is the combination of these motions which generates the figure of eight previously described. We can now safely say that the two experimental facts are now interpreted by our theory.
A very slight difference has been observed between the two sides of the wing in certain insects ; the lower surface is less polished than the upper ; it is furnished with rugosities, hairs, or points, which according to Ohabrier, give more hold on the air and reduce the loss of force by sliding. This disposition may contribute to insure the predominance of the useful effect of the lowering over the elevating motion. Further¬ more, this predominance of the depressing action of the wing does not exist in all insects. These find that force as well in the period of
38
AERONAUTICAL SOCIETY
elevation of the wing as in the period of its depression, turning almost horizontally the plane in which their wings move. The numerous varieties which the mechanism of flight presents among the species of insects which we have observed will be studied later ; they do not conflict with the fundamental principles which 1 have just announced.
The mechanical conditions which we have just' passed in review I have realized in a theoretical apparatus, from which I have obtained the same results as afforded by living insects. This artificial insect is represented by Fig. 8.
An air-pump, moved by a rotary apparatus, alternately compresses and relaxes the air in a tube which traverses the central pivot of the apparatus, where a sort of mercurial gasometer hermetically seals it while permitting the free rotation of the arms. The horizontal branch is hollow, and conducts the air into the apparatus, which is closed by a hollow metallic drum, of which the two circular faces are closed by two sheets of rubber. By the play of the air-pump these two sheets are inflated or contracted both together. They communicate the rapid motions of elevation or depression to the wings by two angular levers. The wings presenting, like those of an insect, conditions of unequal flexibility, decompose the resistance of the air, and impart to the apparatus a rapid rotary motion around the central pivot.
Imagine two artificial wings, as nearly alike as possible, both inserted on one of these little drums, which I have frequently described. They receive through this drum absolutely synchronous motions of elevation and depression. This apparatus is fixed at the extremity of an arm balanced by a counterpoise, and turning upon a pivot. This arm is hollow, furnishing a canal by which the effect of inflation can be trans¬ mitted to the movable drum of the wings. We may consider the drum as representing the body of the insect, and nothing prevents us from really giving it the shape of this animal. The rigid nervures, furnished with flexible membranes disposed to the right and left, will be the two wings, and the animal, instead of being free, will be fixed at the extremity of a movable rod ; there is, therefore, only a single motion possible, which is that of turning around the pivot, carrying the attached rod with it. In effect, if I put the air-pump in motion, the artificial insect moves, flaps its wings, and really flies. At each stroke there is a change of plane of the alar membrane ; at each stroke the point of the wing describes a figure of eight ; and in a general way this theoretical animal, this artificial insect, reproduces all the particulars which the observation of real insects has revealed to us.
This apparatus affords many other advantages besides those of verifying theoretic ideas. It enables us to make new experiments, to which living beings will not lend themselves. We can change one of the conditions, for example, the form of the wings, their extent, or the rapidity of the stroke, or any other of the circumstances, while all the others remain constant ; we may thus discover the influence which each of them singly may have on the mechanism of flight. It is by such experiments that we can assure ourselves of the following fact. In the course traversed by the wing there is only one region useful in the propulsion of the insect ; that is the median region. In the two extreme portions the wing has not experienced that change of plane which renders
Representing the artificial insect or scheme of the flight of insects.
OP GREAT BRITAIN
40 AERONAUTICAL SOCIETY
its action effective. Thus we see if we diminish the extent of the motions of the wing, the tractile power produced by the apparatus diminishes considerably, and finally ceases altogether. If the membrane of the wing is too broad, another phenomenon results. The hinder edge of the wing remains almost immovable in space, especially during motions of small amplitude ; the nervure only is animated with rapid motion. The air, therefore, is struck by planes inclined inversely to those which act upon it in normal flight, so that the apparatus retrogrades and turns around its pivot in a direction contrary to its usual motion.
Experimental flight also shows the adaptation of certain forms of wings to obtain the most rapid translation of motive force. These are precisely the forms which we find in nature. The nervure of insects does not cariy the wing membrane back to its point of insertion. Those parts near the articulation have little vitality ; they contribute very little toward a useful result, embarassing the neighbouring parts, without compensation of any kind. The membrane should not exist except when vitality itself exists in a corresponding degree. Finally, the extent which the alar membrane should have, to best utilize the disposable force, can be determined experimentally. M. de Lucy has compared, in the case of a certain number of animals, the surfaces of the wings to the total weight of the body. He finds an extent of 30 square millimetres in a gnat weighing 3 milligrammes; 1,663 square millimetres in a butterfly weighing 20 centigrammes ; 750 square centimetres in a pigeon
weighing 290 grammes; 4,506 square centimetres in a stork weighing 2,265 grammes ; 8,543 square centimetres in an Australian crane, weighing 9,500 grammes. But to facilitate the comparison it is necessary to reduce these figures to a common measure ; and in spite of the barbarous phrases to which they lead us, we obtain :
Square metres.
The kilogramme of the gnat represents ... ... 10'0
The kilogramme of the butterfly represents .. . ... 8 0
The kilogramme of the pigeon repi’esents ... ... 2586
The kilogramme of the stork represents ... ... 1 '988
The kilogramme of the Australian crane represents... 0'899
The extent of the wings, therefore, is not proportionate to the size of the animal. A wing being given, a maximum rapidity of stroke corresponds to it. To augment the rapidity of the stroke, in hope of indefinitely accelerating the rate of flight, would be illusory ; it is possible to accelerate it up to a certain point, but beyond this maximum limit additions become useless. Increasing progressively the action of the air-pump, the strokes of the wings are more rapid, and at first the rapidity of flight will be augmented. Continue the increase, and the rate of flight diminishes. The amplitude of the motion also experiences a considerable reduction, so that at the limit the wings appear motionless, or animated only by a slight quivering. Passing this extreme limit, the apparatus retrogrades. A given wing then corresponds to a fixed rate of progressive strokes ; for, by the effect of inertia, the frequency of the strokes is increased only at the expense of their extent, and, when the extent diminished, the propelling force diminishes with it. I leave to yourselves the task of explaining these facts, which are the simple
OP GREAT BRITAIN
41
consequences of the principles I have previously explained. I also leave to you the comparison of the mode of progression of insects with the other modes which are seen in other animals or in various mechanical contrivances. You will discover almost everywhere the mechanism of the revolution of forces on the principle of the inclined plane. You will find it in the motion of the tail of a fish, the principal organ of its locomotion ; in the sculling motion of a waterman’s oar, and even in the screw of a steam propeller.
Flight of Birds.
By the simple inspection of a bird’s wing it is easily seen that its mechanism for flight is not the same as that of an insect. Let the manner in which the feathers of birds are laid, one over another, be observed, and it will be evident that the air resists the motion of the wing only from below, so that in an inverse direction it finds an easy passage between the long beards of the feathers, which, in this motion, are no longer pressed together. This well-known arrangement, the effect of which Prechit* has clearly pointed out, has led to the belief that to sustain the bird against gravitation the wing needs only to oscillate in a vertical plane, in consequence of the predominance of the resistance of the air acting from below over that acting conversely.
******
All thin curved bodies tend to slide upon the air in the direction of the radius of their special curve. If we bend thp anterior or posterior edge of our little apparatus at a certain point in its oblique course, we shall see it rise, notwithstanding the force of gravity, though its potion soon ceases. What has happened in this case ?
Fig. 18.
^V7.
Representing to the left Pline’s apparatus placed in equilibrium by means of two equal balls at the extremities of the rod which lies at the bottom of the hngle of the bent paper. This, as is indicated by the lower representations of tfie rod, falls vertically. To the right the same apparatus, with only a single tell, is represented, "it descends in a parabolic curve, represented by the dotted line.
* U ntersuchungen tlber den Plug der Vogel. 8vo. Vienna, l$f6.
42
AERONAUTICAL SOCIETY
When there has been but little rapidity in the fall of the object, the curve of its surface remains motionless, because the air offers resistance only in proportion to the rapidity with which they move. Therefore, when this rapidity has been sufficiently great a steering effect is produced, which elevates the anterior extremity of the object and imparts an ascending motion to it. But very soon the weight, which was the motive
Fig. 14.
line indicates.
power of the apparatus, becomes a retarding force, and in proportion as the object ascends its motion becomes slower, and finally ceases. After this, retrogradation begins, to be followed by another rise, and so on, until by successive oscillations the apparatus finally reaches the earth. I may add that if a slight concavity is given to the object below, the reverse takes place, and we see at a certain moment the trajectory sharply deflected downward, and the object strikes the earth with great violence. In the second case, at the moment when the steering effect is produced, the weight is in a favourable position for a precipitate descent, and opposed to the ascending reaction.
I emphasize these effects because they are frequently produced in the flight of birds. The old treatises on falconry describe the interesting evolutions of the birds employed in hunting. Without going back further, we find in Huber (octavo, published at Geneva in 1784) a des¬ cription of the curvilinear movements of the falcon, to which they gave the name of passades, and which consisted in an oblique descent of the bird, followed by a rise in its course. “The bird,” says Huber, “when about to strike the earth, carried away by its own rapidity, would be dashed to pieces if it did not call into action a certain faculty, which it possesses, stronger than its descending motion, to rise even high enough to make a second swoop. This motion is sufficient, not only to arrest its descent, but even to carry it without effort as high as the elevation from which it came.”
OF GREAT BRITAIN.
43
Fig. 15.
The posterior corners of the paper have been bent downward. After passing through a parabolic curve the object takes a very rapid descending course.
There is certainly exaggeration in the statement that the bird remounts as high as the elevation from which it descended without further effort. The resistance of the air must overcome part of the force acquired during the descent, and which is transformed into ascending force. We see, however, that the phenomena above described is confirmed by observation, and that it has been considered in some sort as a passive act in which the bird expends no muscular power. The act of hovering in some cases presents a great analogy with the phenomena just described. When some birds, pigeons for instance, have used their wings during a certain distance, the wings are seen to be perfectly quiet during a few seconds gliding through the air, either horizontally or rising or falling. The descending motion has the longest duration ; in fact, it is only an extremely prolonged descent in which motion is maintained by the force of gravity, which diminishes it in the horizontal or ascending plane. In these latter forms the wing, more or less obliquely directed, takes hold on the air like the toy kite, with this difference, that motion is imparted to this by pulling the string when the air is calm, while the bird utilizes momentum previously acquired by an oblique descent or previous strokes of the wings.
I have already said that observers have admitted that certain birds, which they call sailors, can sustain and direct themselves in the air by means of the wind alone. This theory appears paradoxical. It is incom¬ prehensible that a bird, motionless in the wind, should not yield to the resistance of the air through which it glides. If the passades or swoops which tlie falcon executes can sometimes carry it against the wind, this can only be a transient effect, compensated for I v being carried away by the wind more rapidly in another moment. However, this theory has been sustained with great talent by some observers, especially the
44
AERONAUTICAL SOCIETY
Count d’Estemo, the author of a remarkable memoir on the flight of birds. “Every one,” he says, “can see some birds practising this method of flight ; to deny it is to deny self-evident facts.” I myself have noticed this mode of flying, but it has seemed to me that it is executed in general under the following special conditions : Along the cliffs of the coast of Normandy I have seen the gulls and sea-mews performing their evolutions without moving their wings. 1 have seen the daws and rooks flying in the same manner around old cathedrals. But the same birds, when they left these special stations, have always appealed to me to use the rowing method of flight ; that is to say, making regular strokes of their wings, sometimes interrupted in the daws by swoops of short duration. I then sought to determine the direction of the wind, and this is what seemed to me to occur : When a bird finds itself in the neighbourhood of a cliff, where the air is calm or agitated by eddies in a contrary direction to the prevailing wind, it can pass successively from the calm to the agitated air, and conversely. A sea- mew surrendering itself to the force of the wind, receives an impulse which carries it with a certain rapidity, and if, by simply turning, the bird enters a region of calm air, it can utilize the impulse which the wind has given it in returning to the height which it had left. Plunging again into the zone of agitated air, it recommences the evolution which I have just described, without moving its wings, except to give them different inclinations, The daws and rooks appear to me to find the same conditions around the cathedral towers. The authors who have reported the most curious cases of sailing flight have observed them in mountainous regions. It is a condor in the Cordilleras, or an eagle in the Pyrenees. The sailing flight has often been described of certain birds of prey, who, in the middle of a plain, rise and turn without moving their Wings I myself have often seen harriers fly in this manner, but I have always determined, also, that in this case the spiral which they describe is altered by the wind, and that the birds are definitely carried to leeward with a more or less rapid motion.
Even when reduced to these limits the influence of the wind on the flight of birds is very difficult to explain. It is complicated by very different conditions in which the motion acquired by the bird, opposed from various directions by the force of the wind, gives rise to the most varied combinations of motion. It is also known that in the upper regions of the air various currents exist, sometimes even in a contrary direction to those which obtain near the surface of the earth, so that the bird, passing from one to another, finds forces which carry it in opposite directions.*
Finally, the question of sailing flight seems to me one of the most difficult to solve. It would be temeritouB to absolutely condemn the opinion of observers upon such vague theories and ideas as we possess upon the subject.
One of the most interesting points in the conformation of birds
* The late Mr. Espy suggested that the phenomenon of sailing in the flight of birds is due to upward currents of air which take place in warm weather, or beneath clouds, and especially up the side of a mountain against which the wind is blowing.— J H.
OF GREAT BRITAIN.
45
consists in the determination of the relations of the extent of the alar surfaces to the weight of the animal. Is there a constant relation between the weight and these surfaces? This question has been the cause of numerous controversies. It has been already shown that if birds of very different kinds, yet of the same weight, be compared, the wings of some species are found to have four or five times the extent of others. The birds which have large wings are usually those which have been called “ sailors,” while those which have the wing short and narrow are generally classed as “rowers.” But if we compare two “rowing” birds with two “sailing” birds ; if, for still closer comparison, we take them from the same family, in older that the only differences shall be those of form, a somewhat constant relation will be found between the weight of the bird and the surface of its wings. But the determination of this relation should be based upon certain considerations, which have long escaped the attention of naturalists. Mr. de Lucy sought to measure the surface of the wings and the weight of the body in all flying animals. Now, to establish a common unit among animals of such different kinds and forms, he reduced all the measures to an ideal type, of which the weight should always be one kilogramme. Thus, after having proved that the gnat, which weighs three milligrammes, possessed Wings with a surface thirty millimetres square, he concluded, in the types represented by the gnat, the kilogramme of animal was supported by an alar surface of ten square millimetres. By making a comparative table of the measures taken from a great number of animals of different kinds and various forms, he arrived at the following figures : —
|
Species. |
Weight. |
Wing surface. |
Surface per kilogramme. |
|
Gnat . |
3 milligrammes... 20 centigrammes 290 grammes . |
30 sq. millimetres . . . 1,663 sq. millimetres.. 750 sq. centigrammes 4,506 sq. centimetres 8,543 sq. centimetres |
10 sq. millimetres 81 sq. millimetres 2,586 sq. centimetres 1,998 sq. centimetres 899 sq. centimetres |
|
Butterfly . Pigeon . |
|||
|
Stork . |
2,265 grammes ... 9,500 grammes ... |
||
|
Australian crane |
From these measurements, in spite of variations in detail, the evident result is obtained, that animals of large size and great weight sustain themselves with a much smaller proportional alar surface than smaller animals. A similar result already shows that the office of the wing in flight is not merely passive, for a sail or parachute should always have a surface proportioned to the weight which acts upon it ; considered, on tne contrary, from its true point of view, that is to say, as an instrument for striking the air, the wing of the bird should, as we shall see, present a relatively smaller surface in birds of large size and great weight. The astonishment exhibited at the result of the determinations marie by Mr. de Lucy disappeared when it was remembered that there was a geometrical reason why the alar surface could not increase in proportion to the weight of the bird. In fact, if we take two objects of the same shape, two cubes, for example, of which one shall be twice as large in diameter as the other, each one of the faces of the larger cube
46
AERONAUTICAL SOCIETY
will be four times as large as the corresponding face of the smaller, while the weight of the greater cube will be eight times that of the lesser one. For all similar geometrical solids, the linear dimensions having a stated relation to each other, the surfaces are as the square and the weight as the cube of their similar linear dimensions. Two birds of similar form, but having, one of them, the spread of the wings from tip to tip twice as great as in the other, will have respective wing surfaces in the proportion of 1 : 4, and weight as 1 : 8. M. P. Demonddsir, who applied these principles before me, thought that he had found in them a reason for the smaller size of birds being capable of flight, while those of a larger kind, such as ostriches and cassowaries, do not fly ; he observes that if these birds had as large wings as the heron in proportion to their weight, they could not fold them completely, and would drag them as long and embarrassing appendages. These observations would be correct according to the theory of “sailing” flight, but, in “rowing” flight, the amplitude of the stroke of the wing, increasing in proportion to the size of the bird, multiplies the resistance which the wing meets from the air, and the reaction bears a similar proportion to the weight of the birds themselves. Dr. Hureau de Villeneuve, upon the same principle, has sought to ‘determine the alar extent which would enable a bat of the same weight as a man to fly. He found that each of its wings would be less than three metres in length.
A remarkable work by Hastings* has appeared this year on the relative extent of the wings and the weight of the pectoral muscles in the different species of flying vertebrate animals. The author first shows that among birds the existence can be established of a certain relation between the surface of the wings and the weight of the body. But we should be careful to compare only comparable elements ; that is to say, the length of the wings, the square root of the alar surfaces, and the cube roots of the weight among different birds. Let l be the length of the wing, a its area, and w the weight of the body, we can compare among themselves l, -j/^ \/v^
Examining different types of birds, Hastings made weights and measurements, from which the following table is extracted : —
|
Species. |
Weight. |
Surface. |
Relation between them. |
|
to. |
a . |
1 /a Vu> d- Vw |
|
|
Laurus argentatus . |
565'0 |
541 |
2'82 |
|
Anas nyroca . |
508'0 |
321 |
2'26 |
|
Fulicaatra . |
495‘0 |
262 |
2-05 |
|
Nettion crecca . . . |
2756 |
144 |
184 |
|
Laus ridibundus . |
197‘0 |
331 |
313 |
|
Machetes pugnax . |
190'0 |
164 |
223 |
|
Rallus aquatlcus . |
170'5 |
101 |
1"81 |
|
Turdus pilaris . |
108'4 |
101 |
2T4 |
|
Turdus inerula . |
88'8 |
106 |
231 |
|
Sturaus vulgaris . |
86’4 |
85 |
2’09 |
|
Bom by cilia garrula . |
60'0 |
44 |
1'69 |
|
Alauda arvensis . |
82'2 |
75 81 |
2-69 |
|
Parus major . . . |
145 |
2-29 |
|
|
Fringilla "spinus . |
10'1 |
25 |
233 |
|
Parus cteruleus . |
91 |
24 |
2-34 |
* Arohives Ne&rlandaises, t. iv. 1869.
OF GREAT BRITAIN.
47
The weight of the pectoral muscles is, on the contrary, in simple proportion to the total weight of the bird, and in spite of the differences which correspond to the different degrees of aptitude to flight with which each species is endowed, we perceive that the proportion of the weight of the pectoral to the total weight is about one-sixth in the greater number of birds.
Each animal capable of sustaining itself in the air must develope a force proportional to its own weight, and should possess an amount of muscle proportioned to this weight ; for, as we have seen, if the chemical action which takes place in the wings of birds be always of the same nature, this chemical action and the power which it generates will be proportionate to the size of the muscular masses. Now, how is it that the wings of birds in which the surface varies as the square of the linear dimensions suffice to move bodies of which the variation is in proportion to the cubes of these dimensions ? Here it is necessary to bring in the theory of power ; that i3 to say, of resistance multiplied by the square of the distance through which it acts in a given time, admitting a uniform rate for the downward stroke of the extremity of the wing in two birds to be compared, and which have the proportion of 1 : 2 in their linear dimensions. The surface of the wings of the larger bird will be, as we have already said, four times as great as that of the smaller one ; now, as the resistance of the air against surfaces moving at the same rate is proportionate to their extent, if we call the resistance experienced by the wing of the small bird r, that for the large bird will be 4r. But these birds, in the downward stroke of their wings do not execute motions of equal amplitude. In the large bird each point of the wing will travel twice as far as the similar part of the smaller bird. If we call the space traversed y, the resistance r, which the wing of the small bird encounters, we shall have ry for the work done by the wing, and 4r 2 y or 8 ry for the work done by the bird. We see, then, that this work increases in the same proportion as the weight of the animals we are comparing.
Another conclusion results from the preceding considerations. If we admit that the wing possesses the same velocity in both birds, the duration of the stroke will increase with the space traversed by the wing ; that is, it will be proportioned to the linear dimensions of the bird. Observation confirms this view by showing that large birds make fewer strokes than small ones do. We have not yet been able to determine exactly the number of strokes of the wings of birds to ascertain if their frequency presents an exact inverse ratio to the size of the animal, but it is easy to see that it is in this manner that the frequency of the wing- strokes of birds varies.
The granhic method, which is easily employed in determining the frequency of the wing-strokes of insects, cannot be similarly employed with birds. It is necessary to adopt some method of transmitting signals from the flying bird to the registering apparatus. For this purpose I have first used the electric teleyraph, which furnishes the means of solving the following questions : — 1. What is the frequency of the strokes of the wings of a bird ? 2. What are the relative durations of the periods of
elevation and depression of the wings ? The experiment consists in placing at the extremity of the wing an apparatus which breaks or closes
48
AEBQ1T4,WICAP ^ppCftTY
an electric circuit at each ot the alternate motions, while at the further part of the circuit is placed an electro-magnetic apparatus, which makes a trace upon a turning cylinder. Fig. 16 shows this method of studying
Fig. 16.
Apparatus for registering the motion of the wing of a pigeon by double signals. In one ease a small India-rubber tube transmits the record of the muscular action ; in the other the periods of elevation and depression of the wing, with their relative durations, are noted by ap electric signal.
Or GREAT BRITAIN.
49
the flight of a pigeon, together with another method of transmitting signals. In this figure the two wires are separated from each other.
The writing style traces a crenulated line, of which the changes of direction correspond to a change in the direction of the motion of the wing.
In order that the flight may be as free as possible, a fine, flexible cord, containing two wires, establishes the communication between the bird and the writing telegraph. The two ends of the two wires are attached to a very small light apparatus which, from the resistance of the air, executes a kind of valvular motion. When the wing is elevated the valve opens, the circuit is broken, and the line traced by the telegraph rises. When the wing descends the valve closes, the circuit is also closed, and the line is depressed.
Applied to different kinds of birds, this apparatus registers the frequency of the strokes of the wing in each. The number of species which I have as yet been able to study is very small ; I have, however, obtained the following results : —
Number of Vibrations of the Wing per second.
Sparrow . 13
Wild duck . 9
Pigeon . 8
Hen -hawk, Brlteo vulgaris, a hawk called in England
and France the “buzzard” or “busard” . 5J
Sereech-owl . 5
Harrier, Circus rufus, marsh harrier of England, buse of France . . 3
The frequency of the strokes varies according as the bird is starting, is in full motion, or at the end of its flight. Some birds, as we know, have periods when the wing is motionless, and when they move by means of the momentum acquired.
It is interesting to observe the relative duration of the periods cl ascent and descent of the wings. Contrary to the opinion expressed by some observers, the descending period is generally longer than that of elevation. The inequality of the two periods is especially evident in birds which have large wings and make few strokes. Thus, while the periods are almost equal in the duck, which has very narrow wings, they are unequal in the pigeon, and much more so in the harrier.
The following figures exhibit the results obtained from several species of birds : —
|
Species. |
Total distance traversed during one complete oscillation of the wing. |
Propo distf Ascent. |
rtional mce. Descent. |
|
Duck . |
6 -66 centimetres per second . |
3-0 |
3-66 |
|
Pigeon . |
7 5 centimetres per second . |
3 0 |
4'5 |
|
Harrier . |
215 centimetres per second . |
8-5 |
130 |
D
50
AERONAUTICAL SOCIETY
It is more difficult than might be supposed to determine the precise instant of the change of direction in the line traced by the telegraph. The attraction of the magnet and the relaxation have an appreciable duration, if the blackened cylinder turns with sufficient velocity to measure the rapid motions which we seek to analyze. The inflections of the line traced by the telegraph then become curves, of which it is somewhat difficult to determine the precise origin. There is therefore a limit to the precision of the measurements which can be made by the electric method. I think that we cannot approximate by this method nearer than jin of a second to the duration of a motion.
Another kind of signal allows the estimation of the frequency of the stroke at the same time that it furnishes indications of the successive action of the principal motive muscles of the wing.
Myographic method. — In 1867 I indicated a myographic method which might be applied without mutilating the animal upon which the experiment was performed. It consists in employing the swelling of a muscle to afford evidence of its changes in length — that is to say, by its contraction or relaxation. Muscles, not being sensibly compressible, cannot change their length without at the same time changing their transverse diameter. A rapid or short, feeble or energetic contraction of a muscle, hence, is accompanied by an increase in diameter, affording the same features of rate or intensity. At each descent of the bird’s wing the great pectoral muscle thus exhibits an increase of size, which can be indicated by the registering apparatus.
I have made use of flexible air tubes of India-rubber in transmitting these effects, a method which has enabled me at times to register at some distance the beating of the heart, the pulse, and the motions of respiration.
The bird flies in an enclosure fifteen metres square and eight metres high. The registering apparatus being placed in the centre of this enclosure, twelve metres of rubber tubing are enough to establish a constant communication between it and the bird. A sort of corset is applied to a pigeon ( see Fig. 16). Under this corset, between it and the pectoral muscle, is placed a little contrivance intended to exhibit the swelling of the muscle. It consists of a small shallow metal basin containing a spiral spring, and closed over by a thin sheet of rubber. This basin, thus closed, communicates with the transmitting tube.
Fig. 17.
Apparatus for exhibiting the contraction of the thoracic muscles of birds. The upper convex face is formed of a sheet of rubber, held up by a spiral spring, and is applied to the muscles. The lower face, in contact with the corset, carries four little hooks which are caught in the cloth and hold the apparatus in its place.
6F GREAT BRITAIN.
51
Any pressure applied to the face of the apparatus depresses the rubber. The air is forced out of the basin and escapes by the tube. If the pressure ceases, the air re-enters the basin in consequence of the elasticity of the spring which raises the rubber. An alternate inspiration and aspiration is by this means established in the tube, and the motion of the air transmits to the registering apparatus a signal of the more or less intense pressure which has been exerted upon the rubber cover of the basin. The registering apparatus I have used in all my experiments is also composed of a basin, covered by a rubber membrane communicating with the transmitting tube. The motion imparted to the first basin is transmitted by the air to the rubber cover of the second. The motions of the membrane of the receiving apparatus, amplified by a lever, are written on the smoked cylinder. Fig. 16 represents the general arrange¬ ment of the experiment in which the electric telegraph and transmission by air are exhibited together. We see the pigeon under experiment furnished with its corset and apparatus for showing the movements of its pectoral muscles. The transmitting air-tube ends at the registering apparatus, which writes on a revolving cylinder. At the extremity of the pigeon’s wing is an arrangement which opens or closes an electric circuit as the wing rises or falls. The two wires of the circuit are represented separately, and two cells of Bunsen’s battery are seen in their connection with the helix, which, furnished with a lever, registers the telegraphic signals of the motions of the wings. One precaution is indispensable — the rubber tube which connects the bird and the apparatus must be prevented from stretching. When the bird flies it raises more or less of the tube, and if this is elastic it will become elongated by its own weight, producing a rarefaction of the air contained in the two receptacles, and the registering lever will trace muscular curves on a descending line. To prevent this inconvenience, the tube may be tied here and there to the telegraphic cord by means of ligatures, taking care that the tube is a little longer than the cord, and that it is not subjected to traction. These precautions being taken, nothing prevents the successful transmission of signals. No trouble need be taken in regard to the elasticity of the tube in a transverse direction ; its walls are so thick that their elasticity is not brought into play by the feeble changes of pressure to which the air they contain is subjected.
The bird is let loose at one end of the enclosure, the dove-cote in which it is ordinarily kept being placed at the opposite end. The bird naturally flies toward the latter. During its flight the tracings repre¬ sented by Fig. 18 are obtained.
The trace is seen to differ according to the kind of bird experimented upon. However, in all the traces we perceive the periodical return of two motions, a and b, which are produced in each vibration of the wing. What is the signification of these two muscular actions ? It is readily seen that the undulation a corresponds to the action of the muscle which elevates the wing, and b to that of the muscle which depresses it. This can readily be proved by comparing the trace of the muscular action in the electric trace of the elevation and depression of the wing. These two tracings, placed one under the other, show that the period of elevation of the wing agrees with the extent of the undulation a, and the period of deoiession with the undulation b.
Pig. 18.
£
Myographic tracings of the pectorals obtained from various kinds of birds during flight. I. Tracing of the tuning- fork to be used in measuring the absolute duration of each muscular motion; this tuning-fork vibrates 200 times a second. II. Tracing of the muscles of a pigeon obtained, as in Pig. 16. III. Tracing of a wild duck. IV. Tracing of hen-hawk V. Tracing of a harrier.
AERONAUTICAL SOCIETY
OF GREAT BRITAIN.
53
But to establish this agreement we must take the unequal rapidity of the transmission of the electric and aerial signals into account. We may consider the electric transmission as instantaneous, while the aerial transmission is at the same rate as the rapidity of sound through the air, that is, 334 metres per second. If the points of the two styles are placed vertically one above another, the tracings will not be exactly superposed, but the electric signal will precede the other by a distance corresponding to a certain fraction of a second, according to the length of the tube which has been employed. We can even compute, from the length of the air-tube, the amount of retardation, but it is more certainly ascertained by a special determination for the particular tube which may be in use. In a previous experiment, motions were simultaneously transmitted by the tube and by electricity, and the discrepancy deter¬ mined. In the apparatus which I am using, the constant discrepancy is •04 of a second. I should therefore set back the electric signals by a corresponding distance, in order that they may agree with the signals transmitted by the air-tube. Fig. 19 shows the superposed tracing from a harrier after correction.
It is easy to understand how the undulations a and b are produced in all the tracings of the muscles of birds. In fact there exist two distinct planes of muscles in the upper part of the region investigated near the end of the sternum. The most superficial is formed by the great pectoral which lowers the wing, the deeper by the median pectoral or elevator of the wing, the tendon of which passes behind the bifurcation of the sternum to attach itself to the head of the humerus. The two superposed muscles act by their swelling upon the apparatus applied to them. The median pectoral swells when it contracts, signalizing the undulation a by its action ; the great pectoral signalizes the lowering of the wing in the undulation b in a similar manner.
We can verify the correctness of this explanation by a very simple experiment. Anatomy shows us that the median pectoral is narrow, and only covers the inner portion of the great pectoral along the keel of the sternum. So if we displace the little apparatus which reveals the motion of these muscles, and carry it further outward, it will occupy a region where the median pectoral does not cover the great pectoral, and the tracing only presents a simple undulation which corresponds to b in the figures.
It is, therefore, sufficiently demonstated that the undulations a and b, in the muscular tracings of the birds upon which I have experimented, correspond exactly to the principal elevating and depressing muscles of the wing ; but we cannot attach much importance to the form of these tracings for deducing the precise nature of the motion effected by the muscle. In fact, these motions appear to override one another. So the relaxation of the median pectoral is probably incomplete when the great pectoral oommences to act. We should expect no more from these tracings than they naturally furnish, that is to say, the number of vibrations of the wing, the greater or less regularity of its movements, the equality, inequality, and energy of each of them. Restricting the enquiry within these limits, the experiments show that the strokes of the wings of birds differ in frequency and amplitude in the different moments
Fig. 19. — Line a represents the electric tracing of the ascent and descent of the wing of a harrier, as furnished by the apparatus. Line 6 is a tracing of a tuning-fork vibrating 20rt times a second. Line c, correction of the electric tracing, which latter does not represent the changes with sufficient abruptness in the figure (a) obtained directly from the wing. Line d, tracing of the action of the pectoral muscles in the harrier by the air apparatus ; a', period of elevation' of the wing ; b', period of depression. Line e will be hereafter referred to; it represents the vertical oscillations of the bird during flight.
Fig. 20.— Showing the difference in amplitude and frequency in the wing-strokes of a pigeon during a flight of fifteen metres. To the left the extended traces indicate the movements at the commencement of flight. This tracing was recorded on a cylinder which moved very slowly, allowing the record of a large number of strokes to be compressed into a small space.
AERONAUTICAL SOCIETY
OF GREAT BRITAIN.
55
of flight. At starting the strokes are fewer but more energetic ; they attain, after the first two or three, a regular rhythm, which they lose at the moment when the animal is about to alight.
We shall find in other experiments more complete indications of the variation of the movements of the wing during the different periods of flight.
Such are the certain indications which can be derived from the method of signalizing established between the flying bird and the registering apparatus. But if it is wise to guard our conclusions by more rigorous experiments, it may at least be permitted us to attempt to discover whether the tracings of these muscles cannot furnish us with further information in regard to the motions from which they are derived. I have elsewhere demonstrated that the form of the motion produced by a muscle "when it is excited varies according to the resistance which this motion encounters. Thus, in applying the myograph to the muscle of a frog, I have seen that if contraction be impeded by an obstacle the duration of the muscular shock becomes greater on account of that obstacle. Theory, also, would foretell us, that if the muscle presents certain modifications in the different phases of its contraction, the result of unequal resistance overcome at different periods, the swelling of the muscle should also present the same phases. If the tr.unng is the exact impression of the motions produced by the muscle, it can inform us of the nature of the resistance which the wing of the bird encounters in the different phases of one of its vibrations.
Let us take the most simple example. As the median pectoral and great , pectoral are very unequal in size, we may suppose that if the
resistance is equal in the two periods of elevation and depression, the
duration of the former would much exceed that of the latter ; and, as exactly the contrary is the case, we may conclude that the rising wing does not strike the air but cuts it apparently with its edge, so that the resistance to the elevation is very feeble, and is very strong to the
depression of the wing. Now, if we examine the tracing of the
depression of the wing we shall find there, within certain limits, the expression of the different amount of resistance which the wing encounters in the different phases of its depression. It is necessary by previous experiments to determine the effect of certain special kinds of resistance, which we may call elastic resistance, in order to better understand the signification of different forms of muscular motion.
Let us take the muscle of a frog, apply it to the myograph, and excite contraction in it by means of electricity. The form of this contraction varies in the following manner under the influence of different kinds of resistance opposed to the action of the muscle : If a weight be suspended to the muscle it gives the tracing a, Fig. 21. If it encounter an absolute obstacle to all further diminution of length, after a few instants of contraction it gives the trace b. Finally, if it encounters an elastic obstacle, as a rubber thread, which presents a surmountable resistance, the muscle gives the curve c. It seems as if these different forms were sufficient to characterize the nature of the resistance that the contraction of the muscle has had to overcome.
In the first case it is the inertia of a body ; now this body submitted
AEECWAtmOAL SOCIETY
66
to the muscular force during a limited period, should have an acedeifeted motion at first and then a diminishing motion. This is precisely what the form of the curve a indicates. In the second case it is not necessary to explain how the horizontal line which forms the summit of the curve o, expresses the cessation of all contraction in the presence of an absolute obstacle. Lastly, in the curve c, the presence of an obstacle is betrayed by a deflection of the curve ; that is, by a change in the rapidity of the motion which produces it ; but the contraction does not cease because the obstacle is not insurmountable, but it becomes slower on account of the greater resistance presented.
I have been able to convince myself that in the above-mentioned experiments the swelling of the muscle presents the same phases as its change of length. In fact, I have transmitted to the myograph the motion produced by the swelling of the muscle, and have obtained tracings identical with the preceding. Finally, wishing to know if the apparatus which I have used would faithfully transmit the different phases of the swelling of muscle, I made the following experiment : I applied the little drum which had served to obtain the tracings from the birds (Fig. 18) to my own biceps muscle, fixing it exactly in plaee by means of a bandage, and put it in communication with the registering apparatus, I then made sudden voluntary motions, as similar as I could make them to each other, but applied to overcome various forms of resistance. In one case I lifted a weight ; in another my hand was absolutely arrested in upward motion by being placed beneath a heavy table ; in still another, I tied my hand to a fixed object with a rubber band which, by a short flexure of my fore-arm, required the utmost efforts of the muscle to irtretch it.
Now the tracings which express the swelling of the biceps in these three experiments reproduce the three types represented in Fig. 21, and
Fig. 21.
show very clearly that voluntary exertions had been subjected to different forms of resistance. I tried to force upon the muscles identical motions in eacb case, which was always a short vigorous flexure, but the nature of the resistance modified these muscular actions which were intended to be similar to each other, and imparted to them the various
OF GREAT BRITAIN.
57
phases and durations which are exhibited in the figure. This being settled, let us return to the muscular tracing of the great pectoral of the bird. I have said that the exact commencement of this motion is undetermined, the elevator of the wing not having fallen into repose before the depressor commences to act, and if we would represent the probable curve of the action of these two muscles from that which the myograph obtains for us, it will be necessary for us to complete the tracing by means of dotted lines as in Fig. 22.
Fig. 22.
Trace of the action of a harrier during flight : a, action of the elevating muscle ; b, of the depiessing muscle. The dotted lines which descend to the axis of the curve complete the probable form of the motions of the two muscles of the wing.
Thus reconstructed, the form of the curves of the elevator and depressor reveals the nature of the resistance which each of these muscles has encountered. The curve a of the median pectoral is that of a muscle acting on a weight ; it seems to indicate that the inertia of the wing is the only obstacle which the elevator muscle has to overcome. The curve b shows us a deflection, during part of which the contraction of the muscle takes a slower motion ; it is here that the resistance of the air is interposed. These things happen, then, exactly as in the experiments which I have made upon my own muscles and those of the frog. But you may ask why the deflection of the curve is not produced sooner ; and if the depressor muscle can rapidly contract for a certain period before encountering sufficient resistailce from the air to impede its motion. This is just what happens ; we have the proof of it in the anatomical disposition of the attachments of the great pectoral muscle. We shall see hereafter how the motion of the humerus around its articulation is produced ; at present I will only say that in the first part of its action the great pectoral in contracting produces a pivot-like motion of the wing upon the head of the humerus, and that in this first motion the muscle does not experience the resistance of the air which retards its contraction an instant later.
5$
AERONAUTICAL SOCIETY
The reader will perhaps consider that an inordinate number of deductions are made from the forms of the curves of the muscles ; but those who will familiarize themselves with the use of the registering apparatus, and in particular with the myograph, will soon be convinced that chance does not enter into the formation, of the curves, but that the details should find their explanation in the dynamic conditions of the production of muscular power.
Motions executed by the icing of a bird during flight. — We have seen, in regard to the mechanism (if the flight of insects, that the fundamental experiment has been that which has shown the trajectory of the point of the wing in each of its evolutions. The knowledge of the mechanism of flight flows, so to speak, naturally from this first idea. The same determination is equally indispensable for the flight of birds, but the optic method is here inapplicable ; the motion of a bird’s wing, while too rapid to be followed by the eye, is not sufficiently rapid to form a persistent impression of its entire trajectory upon the retina. The graphic method, which I have hitherto employed, only furnishes impressions of motions which happen to follow' a straight line, and it is only by combining this rectilinear movement with the revolving cylinder with a smoked surface that the expression of the rapidity with which the motion is effected at each instant is obtained.
The problem is to find the means of registering on an immovable plane all the motions which the point of a bird’s wing makes in space, as if a style had been placed at the end of the wing, and this style traced or rubbed on a piece of paper by its side. It is still further necessary to have a figure of the same nature as the luminous figure of the gilded wdng of an insect, that the piece of paper on which the trace is to be made shall remain motionless in regard to the centre of motion of the wing of the flying bird, or in effect that it shall follow the bird in all its phases of impulsion' through space.
Now, physios teach us that all motion susceptible of registration in one plane can be generated by the rectangular combination of two rectilinear motions. The tracings obtained by Koenig by arming a vibrating Wheatstone’s rod with a style, the luminous figures of musical chords which M. Lissajous has produced by the reflection of a ray of light from two vibrating mirrors perpendicular to one another, are well known examples of the formation of a plane figure by means of two rectilinear movments. Thus, admitting that the motions of elevation and depression of the wing can be transmitted at one time, as well as the back and forward motions of this organ, by supposing that a writing style can simultaneously receive the impulse of these two motions, perpendicular to each other, this point will write on the cylinder the exact figure of the motions of the bird’s wing. I tried at first to construct an apparatus which would thus transmit such a motion to a distance and register it, without concerning myself with the way in which I might apply this rather weighty mechanism to the bird.
Fig. 23 represents this provisional apparatus, the description of which is indispensable for the comprehension of the second mechanism, which I shall describe hereafter. Upon two solid feet, carrying vertical supports, are seen two horizontal arms parallel to each other. These are
OF GREAT BRITAIN
59
two aluminium levers which, by the transmitting apparatus to be described, should both execute the same motions. Each of these levers is mounted on a ball-and-socket joint, or double articulation, which
Fig. 23.
Apparatus intended to transmit to a lever at a distance all the motions executed In another lever around one of its extremi Aes.
60
AERONAUTICAL SOCIETY
permits all kinds of motion ; thus each lever can be carried above, below, to the right, or to the left. It can by its point describe the base of a cone of which the joint will be the apex. In fact, it will execute any kind of motion which the experimentor may choose to impart to it. It is also necessary to establish the transmission of motion from one lever to the other at a distance of ten or fifteen metres. This is done by means of a process with which the reader is already familiar — the use of drums and air tubes.
The lever, which is seen at the left in the figure, is fastened by a metallic arm articulated at one of its extremities to the membrane of a drum placed below it. In the vertical motions of the lever the membrane of the drum rises or falls by turns, producing a throbbing motion of the air in another drum through a long tube, which establishes a communica¬ tion between them. In the apparatus to the right in the figure, the second drum is placed above the corresponding lever articulated with it, and faithfully transmits all the motions which have been imparted to the first drum to the left. These movements will be in the same direction in both levers on account of the inversion of the position of the drums. If we depress the first lever it presses down the membrane of the drum below it, inducing a pressure which lifts the membrane of the second drum and consequently lowers the second lever ; conversely the elevation of the first lever produces an influx of air, which raises the metnbrane of the second lever.
Proceeding in the same manner to transmit motions in a horizontal plane, I have placed at the right of one of the levers and at the left of the other a drum with the membrane in a vertical plane, which imparts lateral motions to these levers ; these motions are transmitted by a special air-tube, as before. In the apparatus thus constructed, if we move the end of one of the levers with the finger, the other lever will be seen to execute the same -movements with perfect fidelity. The only difference consists in a slight diminution of amplitude. This happens because the air contained in the tubes and drums is slightly compressed, and in consequence docs not transmit the whole of the motion which it receives. It is easy to remedy this defect, if it be one, by placing the ball-and-socket joint a little nearer the point whence the motion is transmitted to the second lever. But it is better not to attempt too great amplification, because the friction is thus augmented and the force which should overcome it is diminished.
After having determined that the transmission of such motion can be effected in a satisfactory manner by means of this apparatus, I have sought for the means of tracing these movements upon a plain surface. The difficulty which before presented itself when I endeavoured to apply tne graphic method to the study of the wing-strokes of insects, again appeared, but this time there was no means of eluding it, and I contented myself with partial tracings. The point of the second lever described a spherical figure in space which could not be tangent, except as a point, to the smoked surface, which should receive the trace. In consequence, I should have to register the projection of this figure on the plane. Helmholtz has also encountered the same difficulty in the construction of his myograph, and had solved it by causing the point of the writing
OF GBEAT BEJXAUf.
61
style to rub continually on the smoked surface by means of a weight. But as I could not attach a weight to the extremity of my lever, I resorted to the following expedient, shown at the end of the lever in Fig. 24. It is large at the base in order to resist all lateral deviations
from friction ; this base is fixed on a vertical piece of aluminium which is attached to the extremity of the lever. In this way the point of the contrivance, which performs the office of a style, is situated exactly opposite the end of the lever whose motions it registers. If the lever be elevated and takes the position indicated by the dotted lines in Fig. 24, in traversing this space it has described the arc of a circle, and its extremity will be no longer on the same plane as before, but the elasticity of the contrivance wall have carried the point of the style forward, and it will therefore continue to be in contact with the plane upon which it is tracing. Thus the lever elongates or shortens according as the case requires, and its point continually rubs upon the plane. I should add that the surface upon which the tracings are received is of finely polished glass, and that the contrivance which I have used is so delicate that the pressure which it exercises produces scarcely any friction.
The apparatus being thus constructed, it must be submitted to verification, to ascertain whether the motions are faithfully transmitted and registered. To do this both levers of Fig. 23 are furnished with similar styles placed against the same smoked glass ; and moving one of the levers with the hand, for instance, so as to write my name, the other lever should reproduce the same signature. It frequently happens that the transmission is not equally good in both directions, which is perceptible by the deformity of the transmitted figure, which is increased more or less in height or breadth. This deficiency can always be corrected, since it is due to the membrane of one of the drums being stretched more than that of the other, and hence yielding' less easily to pressure. It is very easy to equalize the tension by tightening the membrane of the other drum until the figure traced by the first lever U identical with that traced by the second.
62
AEE0NAT7TICAL SOCIETY
The modifications by means of which I have rendered this trans¬ mission applicable to the study of the motions of the wing of a flying bird, are as follows : —
The apparatus necessarily being heavy, it required a large bird to carry it. Strong adult harriers served for the experiments. I fixed a light strip of wood upon the bird’s back, upon which the apparatus was placed, by means of a kind of corset, which left the wings and feet free. That the lever might faithfully execute the same motions as the bird’s wing, the joint of the lever should be placed in contact with the humeral articulation of the harrier. As the presence of the drums by the side of the lever does not permit this immediate contact, I had recourse to a parallelogram, which transmitted to the lever of the apparatus the movements of a long arm of which the centre of motion was very close to the articulation of the bird’s wing. Finally, to obtain an identity of motion between the arm and the harrier’s wing, I fixed on the bastard wing, that is to say, on the metacarpal portion of that organ, a well cut screw-vice, furnished with a ring, through which passed the steel arm of which I have just spoken.
Fig. 25 represents the harrier flying with the apparatus in question ; below hang the transmitting tubes of the registering apparatus.
Fig. 25.
Harrier ll.ving with the Apparatus, winch transmits the motions described by the extremity of its wing.
After a great many fruitless attempts and changes of construction of the apparatus, which, being very fragile, broke at almost every flight of the bird, 1 succeeded in obtaining satisfactory results. During flight the registering lever described a kind of ellipse, but I was obliged to give up registering this figure upon a stationary glass. The motions of
OF GREAT BRITAIN.
68
the wing differing at different moments of flight, the style did not pass over the same points, and 1 obtained a very confused tracing. I then resolved to use a glass moving horizontally at a uniform rate in order to obtain an extended figure, which I could afterward submit to a geometric correction, and thus obtained as it would be if traced on a stationary-
surface a figure for each instant of flight.
Fig. 26 represents one of the nume¬ rous tracings which I have thus obtained. The perfect uniformity of these tracings gives me entire confidence in their cor¬ rectness. To analyze the meaning of this curve it is necessary to know how the bird flies, how the apparatus is arranged, and in what direction the smoked glass moves while receiving the tracing. The observer being placed opposite the glass on the smoked side, sees it move from the right to the left ; between the glass and himself is a tracing apparatus with the lever rubbing upon the smoked surface directly in front of him. The bird flying from right to left, in a plane parallel with that of the glass, carries the lever of the apparatus on his right wing, so that the respective levers of the two machines are always parallel to each other. This being known, the tracing should be read from left to right. We have seen that the tracing consists of a kind of ellipse, which the motion of the glass extends into a spiral. The movements, more extended at the beginning of flight, gradually lose a little of their amplitude, and retain a uniform character for some time.
This figure somewhat resembles that which we obtain from a Wheat¬ stone's rod, according to the unison which traces the ellipse which its point describes upon a surface moving from right to left. Fig. 27, showing the tracing of this rod, admits the comparison of the two.
The wing of a harrier thus describes a sort of ellipse, but it is necessary to determine more exactly its shape, and to correct the error caused by the motion of the glass plate.
AERO^trtlCAI, SOCIETY
Pig. 27.
Ellipse traced by a Wheatstone’s rod upon a turning cylinder.
Such a correction is impossible unless we know the elevation attained by the wing at the end of successive and equal intervals of time. This pnce obtained, if we trace parallel horizontal lines representing the position of the wing at each of these successive moments, these lines will cut the descending curve at points which correspond to the successive equal intervals of its course. It is clear that if these successive points of the curve have been produced at equal intervals of time, each of them, under the influence of the motion of the glass plate, will have a constant deviation toward the right, bearing a stated relation to the preceding- point. The correction thus consists in carrying the second point back toward the left twice this amount, the third point three times this amount, and so on. The ascending portion of the curve should also be submitted to this correction, and similarly each part of the tracing. But it is precisely the height which the wing attains in the different ascending and descending motions of its course which we do not know ; but this want can be supplied by the apparatus in the following manner : —
Since the principle of this mechanism is founded upon the trans¬ mission of two motions, perpendicular to each other, vertical and horizontal, it suffices to suppress the transmission of the horizontal motion to obtain the curve of elevation imme¬ diately ; that is to say, the expression of the height of the wing at each instant of its course.
For this I obstruct the tube of lateral trans¬ mission, let the bird fly, and obtain the curve of the heights of the wing at each moment.
The correction being made, and Fig. 26 being selected to show the course of the point of the wing during one of its evolutions, and projected upon a stationary plane, we obtain Fig. 28.
The arrows indicate the direction in which the wing moves. Course in space of the
Is this the form characteristic of all birds ; extremity of the wine, re- or is it only that of tl^e hai rier in the conditions °m t*'° lnot*<" °*
of flight in which it has been placed ■
OP GBKAT BBITAIW,
65
The last supposition appears to be the most probable ; we can see, even while comparing the form of the tracing at different instants of its flight while under experiment, that the ellipse is greater and more open in the first strokes of the wing than in the last. It is, however, necessary to except the second stroke of the wing, which has given me a narrower ellipse than in any other in all the experiments which I have made. I do not know to what this special form is to be attributed, but have thought it worth while to mention it on account of its constancy.
Of the rotation of the humerus and the changes of the plane in the wing during flight. — The wing of a bird, like that of an insect, must meet with a sufficient resistance from the air in its motion upward and down¬ ward to incline its flexible portion, namely, that which forms the webs and coverts. This cause does produce, a change of the plane of the wing, but there is another even more powerful, for it places the wing at the outset of the depressing motion in a favourable position for the double propulsion which iB produced. I refer to the pivot motion which the humerus executes around its axis at each contraction of the great pectoral. It is enough to examine the bony crest on which the large tendon of the great pectoral is inserted, and to consider that this crest is situated on the anterior edge of the humerus, to comprehend that the action of the great pectoral, whose fibres are carried backward and downward, should produce a rotary motion of the humerus around its longitudinal axis. The conformation of the humeral articulation is perfectly adapted to this motion. Finally, the existence of this rotation is rendered still more necessary by the resistance which the air presents to the back of the wing and opposes to the descent of its feathered portion. We can demonstrate the existence of this motion and measure its extent by means of the registering apparatus. But I have thought it best to defer these researches, especially as they necessitate the construction of special apparatus, which would require numerous experi¬ ments, and would produce, after all, results of very slight importance. In fact, we are enabled to deduce from the attachment of the muscles the nature of the motion which they produce, and this deduction is especially easy.
I have always sought to verify the existence of this rotary motion of the humerus, and to measure its extent, by the application of electricity to the muscles of the bird. In the experiment for measuring the static power developed by the contraction of the great pectoral muscle, previously described, I noticed that at each excitement of this muscle the humerus executed a rotary motion upon its axis. I fixed in the humerus a rod, • erpendicular to its axis, and was enabled, by the angle formed by the two positions of this rod, to demonstrate that the rotation in the harrier corresponded to an angle of thirty-five or forty degrees. It seemed that the limits of this angle were fixed by the attachments of the median and great pectoral muscles. If .traction be exerted upon the two antagonistic muscles of a newly-dissected bird, it will be seen that the median pectoral raises this member so that its upper face is turned somewhat backward. The action of the great pectoral changes this position of the wing completely, and carries its upper face strongly upward and even a little forward. These expressions, upward and
E
66
AEKONAUTIOAL SOCIETY
downward, are relative to a plane cutting the bird into a dorsal and a ventral half ; but this plane, doubtless, is not entirely parallel with the horizon during flight. But it is certain that the resistance of the air should give a much more pronounced deflection to the feathers during the more rapid descent of the wing.
The most difficult to measure of the influences which change the plane of the bird’s wing is that which relates to the pressure of the air on the feathers. Perhaps it may not be impossible to devise an apparatus capable of measuring it, but it so varies with the variations of the velocity with which the wing is lowered, that any measurement which might be obtained would be only the expression of a particular case. It is very probable, on the contrary, that the change of plane due to the action of the pectoral muscles is a much more constant phenomenon. We can infer the action of the two motions of the bird’s wing from what has been said of the mechanism of the flight of insects. It is evident that the descent of the wing will have the double effect of raising the bird and of imparting to it a horizontal motion. As to the ascent of the wing its office cannot be the same, because the imbrication of the feathers does not offer a resistant surface to the air.
Everything tends to show that the ascending wing cuts the air with its anterior edge, but, as we shall see, another phenomenon occura which uplifts the body of the bird during the elevation of the wing ; this is the transformation of the impulse which the bird has acquired during the lowering of the wing. This impulse is changed tn rising, by a mechanism analogous to that which raises the toy kite.
In a remarkable study of the flight of birds, M. Liais has been led, through observation and deduction, to adopt this theory, to which the experiments about to be described, I trust, will add new proofs in its favour.
Before leaving the subject it is necessary to mention the existence of certain other motions in the flight of small birds. I refer to the folding and unfolding of the wings. But the existence of these motions does not seem to be constant, and the eye cannot perceive the least trace of them during the flight of the large birds upon which I have experi¬ mented. I shall, therefore, omit the study of these motions, and of their possible effects, and restrict my conclusions on the mechanism of flight to a certain number of determinate species of birds.
The study of the motions of the wings of birds during flight necessarily includes the effect produced by each of these movements. We are tempted to deduce these effects from the nature of the motions which generate them, but it is safer to obtain the solution of this complicated problem from experiment. Two distinct effects are produced during flight : first, the bird is upheld against the force of gravity ; second, it is propelled horizontally. Is the bird in the air sustained at a constant elevation, or is it rather subject to oscillations in the vertical plane? Does it not exhibit, by the intermittent effect of the strokes of its wings, a series of ascents and descents, the frequency and extent of which cannot be observed by the eye ? Is not the bird also subjected to a variable velocity in its horizontal course? Does it not receive a jerking motion from the action of its wings ? These questions can be
OF QREAT BRITAIN.
03
solved by experiment in tbe following manner : Since we possess the means by which distant motions produced by pressure exerted upon a drum filled with air are made to record themselves, we must seek to connect the movements which we would study with a pressure of this kind. The oscillations which the bird executes in the vertical plane should be made to produce alternately strong or feeble pressure on the membrane of the drum, according as the bird rises or falls. The same should be done in seeking the variations of its horizontal velocity. Suppose that a flying bird carries upon its back a light metallic drum, like the one already described ; that the membrane of this drum be Turned upward, and that this instrument be put in communication with the registering apparatus by means of a long tube. If the membrane of the drum freely partakes of the motions of the bird it will not produce any displacement of the air in the apparatus, and the registering lever will remain motionless. But if we prevent the membrane from partaking of all the motions of the bird, if we can give it a tendency to remain at rest while the drum is moved, motion will be produced in the air with which the drum is filled, and the signals will be registered by the lever. Now, we can produce this tendency to remain at rest upon the membrane by loading it with an inert body, such as a disc of lead.
Fig. 29 shows the drum with an inert mass upon its membrane. This mass is formed of discs of lead, of which a certain number can be added or taken off, until the apparatus responds satisfactorily to the motions of vertical oscillation imparted to it. In this arrangement the movements in the horizontal plane are without influence upon the apparatus. If the drum is suddenly raised, the inert body, not participating in this elevation, depresses the membrane exactly as if the mass itself had been depressed and the drum had remained motionless. Conversely, when the drum descends, the inertia of the mass resists the motion as if it or the membrane had been raised and the drum had remained motionless. We may remark that the movement of the lever is in the same direction as that of the drum ; that is to say, if the drum be raised the lever also raises itself. It may happen with an apparatus of this kind, that in the motion of the wings rubbing may be produced on the membrane of the drum which will make confusion in the signals. To avoid this I cover the upper part of the apparatus with a metallic network, as seen in Fig. 29. The drum is there represented in the hand, held by the transmitting tube connecting with the registering apparatus, ff the drum is moved in the vertical plane the lever is seen to move in the same direction, at the same instant of time, and with an amplitude proportionate to the motions of the hand. If, on the contrary, we give the mass a lateral motion, no effect is produced upon the lever and no signal is made. But it may be said that an inert mass placed on an elastic membrane tends to execute vibrations peculiar to itself, and that the apparatus will transmit these vibrations of the mass of lead and the membrane which carries it independently of the oscillations of the bird. How shall we get rid of this complication ? The law of vibrations teaches us that the duration of the double period of each of them varies with the weight of the vibrating body and with the elastic force of the lamina which carries it. The greater the mass and the feebler the elasticity
s
Fig. SO.
Line 1. Chronographic trace of a tuning-fork vibrating 100 times a second. 2. V ertical oscillations of the wild duok during flight. S. Oscillations of the hen-hawk. 4. Of the screech-owl. 5. Of the harrier.
OF GREAT BRITAIN,
70
AERONAUTICAL 80CIETY
mission of motions, which are not too slow, may be obtained, for instance, such as last less than half a second. It is not necessary, either, that the instrument should be applied to the study of the oscillations of all species of birds.
But to make sure of the accuracy of the apparatus it should be verified by the method much like that which I have used to correct all my apparatus. This consists in making directly, by hand, the tracing of the motion which I have imparted to the weighted drum, and observing whether the registered motion was the same as the first.
Experiments made upon different kinds of birds, ducks, harriers, hen-hawks, and owls, have shown me that, in relation to the intensity of the oscillations in the vertical plane, very varied types of flight exist.
Fig. 30 shows tracings, furnished by different kinds of birds, upon a cylinder turning at a uniform rate, and contrasted with a tracing produced by a tuning-fork making 100 vibrations per second. These tracings enable us to estimate the absolute and relative duration of the oscillations of flight in these different birds. It follows from these figures that the frequency and amplitude of the vertical oscillations vary a good deal with the kind of bird under consideration.
Fig. 31.
In the upper half is Seen superposed the musenlar tracing and that of the vertical oscillations in a wild duck. Below the undulation a, which indicates the elevation of the wing, is seen a vertical oscillation ; and another, below b, which indicates the lowering of the wing. In the lower portion are the same tracings obtained from a harrier; here the oscillation at a, which corresponds to the elevation of tho wing, is less marked than in the duck.
OF GREAT BRITAIN.
71
To better comprehend the cause of these variations, let us register at the same time the vertical oscillations of the bird and the action of the muscles of its wing. If we make this double experiment upon two birds, differing in their manner of flying, such as the wild duck and the harrier, the tracings represented by Fig. 31 will be obtained.
The duck presents two energetic oscillations at each revolution of its wing ; the one at b, at the moment when the wing relaxes, is easily understood ; the other, at a, at the moment when the wing rises. To explain the ascension of the bird, during the time of elevation of the wing, it seems to me indispensable to call in the action of the boy s kite, previously alluded to. The bird, moving forward with acquired velocity, presents its wings to the air in an inclined position similar to that of the kite, and thus transforms its horizontal force into an ascending one.
The flight of the harrier presents the ascension which accompanies the elevation of the wing in a smaller- degree. May not the cause of this difference be recognized as a smaller relative inclination of the wing toward the horizon ?
Determination of the different phases of the evolution of the mng to which the vertical oscillations correspond. — The interpretation of. these curves throws light at once upon the experiments made on the variations of the transformation of velocity in the bird, at different moments, during the evolution of the wing. ,
But, before going further, we may remark that the preceding experiment furnishes a very precious lesson in the theory of flight.. In fact, if the bird excutes a series of ascents and descents, the duration of the descending period will approximately inform us of the amount of. the positive work which the bird must perform to rise again to the height from which it fell, and we see that the duck, which makes nine vibrations of the wing per second, executes two vertical oscillations during each vibration, or eighteen in a second. Each oscillation is composed of a rise and fall, so that each descent of the bird cannot last more than one thirty -sixth of a second. Now, if we subtract the effect produced (as in a parachute) by the outspread wings of a bird, we find that a body which fo.Ua during one thirty -sixth of a second traverses only fifty-two milli¬ metres. This fall repeated eighteen times a second constitutes a total rise of 9 36 centimetres, necessary to maintain the bird in the same horizontal plane during one second.
In the tracing of the harrier, the descents are less than in the wild duck, probably on account of the large surface of the wings of this bird.
Determination of the variations of the rapidity of JUgbj,.—' The second question to be solved relates to the determination of the various phases of rapidity of flight. The solution can be found in the following manner : If the weighted drum be placed upon the bird’s back in a vertical plane perpendicular to the direction of flight, it will be insensible to vertical oscillations, and will only indicate those of forward and backward ; also, by turning the membrane of the drum forward it is clear that if the advance of the bird is accelerated, the retardation of the weight on the translation of the apparatus will produce a crowding of the air in the second drum, and an elevation of the registering lever, while a relaxation of the effort of the bird will bring about a descent of the registering
72
AERONAUTICAL SOCIETY
lever. Experiments upon the kinds of birds previously mentioned furnish tracings anal ago us to those of the vertical oscillations. If it is true, as I suppose, that the vertical oscillation of the bird at the moment of raising the wing be due to the upward transformation of velocity, by obtaining, simultaneously, the tracing of the vertical oscillations and those of the variations of velocity, we shall have the means of confirming this theory. When obtaining at one time the two kinds of oscillations in the flight of a harrier, I have seen that the phase of descent of the wing resulted both in the elevation of the bird and the acceleration of its speed. This effect is the necessary consequence of the inclination of the plane of the wing at the moment of its descent, as we have previously shown in the flight of insects. As for the phase of elevation of the wing, it is proved that during the slight ascension which it produces the speed of the bird is diminished. In fact, the curve of the variations of rapidity falls as soon as the bird begins to rise. This is, then, a confirmation of the previously suggested theory of the upward transformation of the speed of. birds. Thus by this mechanism the descending stroke of the wing creates the force which produces the two oscillations of the bird in the vertical plane. The downward stroke directly produces the ascent which is synchronous with it, and indirectly by creating the velocity which prepares for the second vertical oscillation.
Simultaneous tracing of the two kinds of oscillation of the bird. — Instead of representing each kind of oscillation separately, I have thought that it would be more instructive to obtain a single line which, by its curves, should represent both of the movements which the body of the bird executes in its course through space. The method which has been used to obtain the curve of the point of the wing, with some modifications, can be made to furnish a simultaneous tracing of both kinds of motion. For this both drums must be connected with the same inert mass, and placed at right angles to each other. Turning back to Fig. 23, which shows the two levers connected by tubes which transmit to the one all the motions executed by the other, when any motion is imparted to the first lever, the second lever reproduces the same motion in the same direction. Now, let us charge one of the levers with a mass of lead, and, taking the support of the apparatus in the hand, make it describe some motion in a plane perpendicular to the direction of the lever. W e see that the lever No. 2 executes directly opposite movements. In fact, since the motive force which acts on the membranes of the drums is simply the inertia of the mass of lead, and since this mass is always behind the motion given to the apparatus, it is clear that if the whole be raised the mass will keep the lever down ; if the whole be lowered, the mass will raise the lever ; if it be carried forward, the mass will hold back the lever, &c. Now, the second lever, executing the same motions as the first, will give curves which are directly the opposite of the motion which has been given to the support of the apparatus. This being settled, nowr for the experiment : — For this I take the apparatus represented on the back of the harrier in Fig. 25 ; 1 remove the rod which receives the motion of the wing, and the parallelogram which transmits it to the lever. I keep only the lever connected with the two drums and the mounting which attaches it to the bird’s back. I fix a
Fig. 32.
Or GREAT BRIT AIK,
73
mass of lead on this lever and, let the animal fly. The tracing obtained is represented by Fig. 32.
The analysis of this curve is at first sight extremely difficult. I hope, however, to succeed in showing its signification. It is traced on the cylinder under the same conditions as Fig. 26, show¬ ing the different motions of the point of the wing. The glass plate moves from the right to the left ; the tracing is read from left to right. The head of the bird is toward the left ; this flight is in the direction of the arrow. We can divide this figure by vertical lines passing through homologous points, cutting it either at the top of the loops or at the summit of the simple curves, as represented at the points a and e. Each of these di¬ visions encloses sinplar elements, although their development is unequal in different parts of the figure. For the present we shall neglect these details.
It is evident that the peri¬ odical return of similar forms corresponds to a return of the same phases in an evolution of the bird’s wing. The division a t thus represents the different mo¬ tions of the bird during an alar evolution.
Let us recollect that in the curve which we are analyzing all the motions are the reverse of those which the bird really executes. The two vertical oscil¬ lations, the great and the small, should then be represented by two downward curves. It is easy to recognize them in the great curve afi'b and the small curve cde. Thus the bird rises from a to b, falls from b to c, again rises from c to d, and re-descends from d to e; but these oscilla-
74
AEBONATTITCAL SOCIETY
tions encroach on each other, producing the loop cd. The oscillation ede partly covers the first anteriorly. This is a proof that the indications of the curve are the reverse of the true motion ; for, at this moment, the bird recedes, or at least relaxes its course. As the apparatus is only sensible of changes of velocity, it is clear that the tracing does not take the uniform rapidity of the bird into account, but indicates acceleration as a forward movement and retardation as a retrograde movement. This figure, then, sums up all the preceding experiments which we have made on the motions of the bird in space. It is here seen that the bird at each evolution of its wings rises and falls twice successively ; that these oscillations are unequal ; the larger, as we know, corresponding to the depression of the wing, the smaller its elevation. It is also seen that the ascent of the bird during the raising of the wings is accompanied by a retardation of its speed, which justifies the theory by which this ascent has been considered as made at the expense of the bird’s acquired velocity. But this is not all ; this curve also shows us that the motions of the bird are not the same at the beginning and end of flight. We have seen already (Fig. 20) that the first strokes are more extended than the others ; we now see that at first — that is, at the left of the figure — the oscillations produced by the descent of the wing are also more extended. But theory foretold that the oscillation of the elevation of the wing being derived from the acquired speed of the bird should be very feeble at the beginning of flight when the animal has acquired but little impetus. The figure shows us that this does happen, and that at the beginning of flight the second oscillation (which forms the loop) is very insignificant.
At last, then, we are in possession of the principal facts upon which the study of the mechanical power developed by the bird during flight can be established, and we see that it is during the descent of the wing that the entire motive force which sustains ana directs the bird in space is created.
OF GREAT BRITAIN.
75
CONCLUDING REMARKS.
One of the most important events in connection with Aeronautics during the past year has been the trial of M. Dupuy de Lome’s navigable balloon. This balloon was constructed by M. de Lome for the Government of National Defence, at a cost of £1600., and was intended to open a communication between Paris (then besieged by the Prussians) and the departments. But, owing to unavoidable delays, it was not finished until just four days before the capitulation. Then came the Commune, and all the disorga¬ nization which followed it ; and it was not till the 2nd February, 1872, that M. de L6me was able to ascend on a trial trip from Fort Neuf at Vincennes.
Before describing the balloon and the ascent, it may be as well to say a few words as to the enu which the eminent engineer proposed to himself. He did not pretend to be able to successfully contend with the wind, but only to deviate from the direct set of the wind when running before it; so if the wind set straight from Paris to Brussels an ordinary balloon could only land at some point between Paris and Brussels, but with M. de Lome’s balloon the aeronaut might deviate from the wind’s course, and descend at London or Cologne as he saw fit.
The following is a description of the balloon as given in M. de Lime’s report read before the Academy of Science. The form of the balloon is oval, its diameter being about
wo-fifths of its horizontal length.
Total length from end to end . . 118ft. 6in.
Diameter at the point of greatest circumference. 49ft. 2in.
Diameter of the screw . . . .... 29ft. 6in.
Number of blades . . . 2
Pitch of screw . 26ft. 8in.
.76
AJEHOKA.TJTIOAL SOOHETY
The rudder is a plane triangular surface, made of unvarnished calico, and is kept in its place by a horizontal beam six metres long at its lower extremity. It can turn easily on its forward extremity. The height of the rudder is 5 metres, and it has a superficies of 15 square metres. The car is of wicker-work, and of sufficient size to contain comfortably the windlass for the screw, and eight men to work it ; the ventilator with which to manage the small bal¬ loon (we shall have to speak of this presently), and the man who attends to it. In all, fourteen persons can be carried. The driving screw is directly carried by the car. The shaft of the screw is a hollow steel tube. This shaft is constructed so as to allow of the screw being easily dismounted when a landing is effected. The rudder is fixed to the balloon itself, and the screw, as we said, is below it, and immediately attached to the car. Two blades only are used in the screw instead of four, because when the ground is touched the two blades can be placed horizontally, so as to escape injury. Were there four blades, the screw would be almost certain to be broken at every landing. The windlass which turns the screw is worked by four, or, if necessary, eight men, in a similar manner to the steering wheel of a ship, only the wheel is placed parallel to the axis of the car, instead of at right angles to it, in order to lessen the rolling occasioned by the movements of the men working the windlass.
The material of which the envelope of the balloon is composed is white silk, weighing 52 grammes, not quite 2oz. to the square metre; and a coarser lining weighing 40 grammes the square metre, and seven coats of india-rubber, which together weigh 180 grammes, a little over 6oz. the square metre. Thus the whole weight of the external web of the balloon is 272 grammes, about 9oz. to the square metre. In order to render the web of the balloon totally impermeable to the hydrogen gas with which it is inflated.
n
OF GREAT BEITAIW.
the silk was painted over with a sort of gelatinous compound* invented by M. Dupuy de Lome. The total weight of the two balloons when ready to start was 570 kilogrammes, or rather more than half a ton. The web of the balloon was reckoned to be capable of supporting a pressure of over 2000 pounds to the square yard. The smaller balloon is, more correctly speaking, only a portion as it were of the larger balloon. It is formed by means of an inner skin, separating the bottom of the balloon from the rest. This compartment occupies about one-tenth of the whole capacity of the balloon, and serves to keep it stiff and of the required shape. By these means M. Dupuy de Lome has attained the two ends he proposed to himself, viz., first, permanence in the shape of the balloon ; and, secondly, an axis unquestionably parallel to that of the force of propulsion.
M. de Lome calculated that the resistance to the balloon at a speed of 7ft. 5in. per second, or 8 kilometres an hour, would be 25lb8., and that this speed could be obtained by
2 1 revolutions of the screw per minute.
We will now describe the ascent: — There was half a gale of wind blowing at the time, and the screw had been slightly damaged. The inventor did not hesitate, however, to make the ascent. The end justified his confidence, for not only was he able to land near Noyon, in the Depart¬ ment of the Oise, some seventy miles north-east of Paris, but his balloon more than answered his expectations. The screw, when worked by four men, drove the balloon 8 kilo¬ metres (about 5 miles) an hour quicker than the rate at which the wind was blowing. By the use of the rudder the course of the balloon could be altered 1 1 degrees either way from the set of the wind, making a total deviation of
22 degrees. The screw when worked by eight men drove the balloon at the rate of 10 \ kilometres per hour. The
AEBOWAUTICAi flOOrEXY
28
number of revolutions at this speed was 27^ per minute, and the power required was 26,400 foot-pounds per minute. The slip of the screw was 24 per cent. Although the speed obtained was not great compared with tbe velocity of an ordinary wind, yet by employing an 8-horse power engine in place of the eight men, a speed of 22 kilometres per hour would have been obtained, which would enable the balloon not only to deviate from the wind, but to struggle against it when moderate.
Experiments with aerial screws have occupied attention during the past year. One correspondent, Mr. Ling6eld, has constructed a piece of apparatus consisting of two superposed screws, rotating in opposite directions ; he found that there was no advantage in using four blades, but that an equally good or better effect could be obtained by means of two blades by which he caused a lifting force of 14£lbs. by his own muscular strength. Having a suspicion that the friction of the surface of the fabric absorbed a considerable per centage of the power, he pasted tissue paper over the calico of the vanes, and thus increased the lifting force to I8lbs.
This proves the importance of attending to the question of friction in aerial mechanism ; to diminish it as far as possible on the surfaces of supporting planes gliding on air, and in reciprocating or oar-like propellers, when possible, to utilize friction as an aid in gaining additional abutment or hold on the air, a principle probably made use of by some birds.
Similar experiments have also been made in Paris by which a lifting force of 26£lbs. was obtained. But these results, though obtained by independent experimenters both here and on the Continent, must not be taken as conclusive of a maximum effect, for probably a far higher reaction- or force against gravity may ensue from more suitable forms of screw, and in the best means of giving them* motion.
One difficulty has been a ready means of varying the angle
OT GRXAT BRITAIN.
79
or pitch of the screw, in order to suit the velocity of .rotation and the force applied. Mr. Wenham has proposed a simple kind of screw for this purpose, constructed in the following mannner : — a is a hollow spindle or tube, at the end of which
80
XEROtfjLtTTICAL SOCIETY
is fixed a cross-socket b, with two arms. Sliding on the spindle loosely is a similar socket, c. Into the ferrules of these two pairs of sockets, taper flexible wands, d d, are thrust ; these are shaped like billiard cues, and made of light elastic wood. From the extremities of these to near one-third the distance towards the centre a piece of fabric, ee, is sewn between them. A light iron rod passes through the hollow spindle, having a short cross arm at the outer end. Two return rods from this, afford the means of compression to a spiral spring f, surrounding the spindle, and resting on the sliding socket c. At the lower end of the spindle there is a cross-handle g , tapped to receive the screwed end of the inner rod. By turning this handle the spring is compressed, forces down the lower sliding socket, and of course gives any required tension to the fabric connecting the rods or arms of the screw. In this condition the four arms and planes of the fabric coincide with the axis, but if this is set in rotation, the two lower arms and socket being free thereon, are forced back by the resistance of the air, giving an inclined position to the fabric of the proper form for an aerial screw, with a somewhat hollow face or expanding pitch, which can be exactly determined by the tension given to the spring ; if this is slack the pitch will be a fine one, and when screwed hard up the lower socket will yield but little, and a coarse pitch be obtained.
As the rods twist or deviate from each other, of course the connecting distances between them become greater at the extremities than near the centre. This is compensated for — 1st, by leaving the middle as an open space ; 2nd, by having the fabric loose at the extremity, so as to meet the coarsest pitch required ; and 3rd, the rods being properly elastic at the ends, yield so as to stretch the fabric uniformly in fine pitches, giving the blade of the screw a taper form, which is not an objectionable one, but the reverse.
6f OftBAT BRITAIN.
81
iTie grfeat advantage of this self-compensating aerial screw is its portability. The rods may be pulled out of the sockets, and rolled up together with the fabric as one piece in a compact form.
There is a peculiar feature connected with the working of this Society to which it may be as well to allude, viz., its apparent inactivity.
The work which is surely being accomplished is effected under a variety of conditions by private individuals, but almost always under circumstances of discouragement within the experimenter’s private circle.
In these cases the moral support of the Society is consider¬ able. The Council feel that of theory we have had almost enough, and that however much the publication of the Papers read at the General Meetings may have cleared up some of the apparently insurmountable difficulties attending the subject, the continual expression of opinion is liable to become rather wearisome.
We now require and look for facts, and for these we would wait before 'we call upon members to discuss them.
The Council perceive that those of the members who are not actually engaged in experiments perfectly acquiesce in this view by the patience with which they wait the very few Public Meetings of the Society.
It is not, however, in these Meetings that the real business of the Society is effected. The Secretary has a large correspondence, and the calls upon his time in interviews, both at home and abroad, are more than could be expected from any one less interested in the subject.
It is the knowledge of this which induces a few members of the Council to render all possible aid by meeting for (consultation and in furtherance of the attainment of results.
F
82
AERONAT7TIOAX SOCIETY
Dr. W. Smyth wishes in this number to make the following remarks relative to a Paper read by him and printed in the Second Annual Report. He feels it the more necessary because of his statement having been quoted by various authors. “ After reflection upon the experiments performed by me in dividing the nerves of the wings of pigeons, I am of opinion that they were inadequate to determine whether the pigeon could fly or not with all sensation severed. The experiments were hastily performed for a coming Meeting of the Society, and I judged it to be as reported at the time, but as the experiments are being quoted by others I desire their actual value to be correctly known."
OF GREAT BRITAIN.
83
MEMBERS.
Alexander, A., C.E., 13, Cyclops Steel and Iron Works, Sheffield; of the Council
Arbothnot, H. Gough, 40, Prince’s Gate, s.w.
Argyll, His Grace the Duke of ; President of the Council Armour, James, C.E., Gateshead Ashbury, J ames, 66, Grosvenor Square, w.
Ballard, Stephen, C.E., Colwall, Great Malvern Barber, William, 9, “The Boltons,” Kensington, w.
Baring, Colonel, 36, Wilton Place, s.w.
Barnett, E. W., 25, Lancaster Gate, w.
Barrett, Frederic, Langley House, Grove Lane, Camberwell, S.E. Baxter, Richard, F.R.G.S., 19, Leinster Gardens, w.
Beadon, Captain R.N., Creechbarrow, Taunton
Bennett, T. J., 20, Little Clarendon Street, Oxford
Borthwick, Lord, 35, Hertford Street, May Fair
Bourne, John Fred., C.E., Louth, and Civil Service Club
Bourne, Edwin, 3, Stafford Street, Wellington, Salop
Bovill, William Edward, 22, James Street, Buckingham Gate, s.w.
Bowden, A. J., 41, Lamb’s Conduit Street
Bowles, Thomas G., 88, St. James’s Street, s.w.
Breabey, Fred. W., Maidenstone Hill, Blackheath ; of the Council, and Honorary Secretary
Bright, Sir Charles Tiltston, F.R.A.S., Lancaster Gate ; of the Council
Brooke, Charles, M.A., F.R.S., 16, Fitzroy Square; of the Council
Brooks, Maurice, 10, York Terrace, Regent's Park
Brown, Rev. J. T., M.A., 47, Clifden Road, Lower Clapton, E.
Brown, David Stephens, Braywick House, Green Lanes, Stoke Newington
84
AERONAUTICAL SOCIETY
Browning, John, F.R.A.S., 111, Minories; of the Council Brcnton, N. W., 116, Belsize Park Gardens, n.w.
Burnaby, Captain, Royal Horse Guards
Bcrrell, Edwabd, The Hermitage, 7, Melina Place, St. John’s Wood Burton, Rev. Roger Taylor, M.A., Lexden Villa, near Colchester Butler, William Fred., C.E., 5, Cannon Row, s.w.
Chaplin, James C., 12, Craven Hill, Hyde Park Childs, Thomas, Inver House, Chiswick
Clare, Walter F., Engineer, 2, Agnes Cottages, Elm Grove, Hammersmith
Clarke, Charles, 1, Coburg Place, Bays water Road Crestadobo, Dr., Free Libraries, Manchester Dawson, G. J. Crosbie, 7, Queen Square, St. James’s Park Deobuz, E., Seetarampore Colleries, Raneegunge, Lower Bengal, India Delane, John T., 16, Serjeants’ Inn, Fleet Street De Villeneuve, Dr., 13, Faubourg Montmartre, Paris Diamond, Hugh W., M.D., F.S.A., Twickenham House ; of the Council Duff erin, Earl of, 8, Grosvenor Square ; Vice-President of the Council
Fairbairn, Sir William, Bart., LL.D., F.R.S., Manchester Gabbtang, James, Bank-top Foundry, Blackburn Glaisheb, James, F.R.S., F.R.A.S., &c., Blackheath ; of the Council Greenfield, Captain J. Tyndall, 17th Brigade R.A.
Gbketham, Thomas, 68, Lincoln’s Inn Fields
Gbosvenqb, Lord Richard, M.P., F.R.G.C., 76, Brook Street, w. ;
Vice-President of the Council Haghe, A., Fern Lodge, Stockwell Green Hall, George Samuel, Springfield House, Acton, w.
Hammant, W., 32, Bouverie Street, Fleet Street
Habrison, A. Stewart, 133, Upper Thames Street
Habte, Richard, 2, Devonshire Terrace, Notting Hill
Hay, Rear-Admiral Lord John, 149, Piccadilly; of the Council
Hodges, F., Leicester
Holland, Robert, Stanmore, Middlesex
Howell, Charles Augustus, C.E., F.S.A., Northend Grove, Northend,
t “
Fulham
85
0* GKKAT BRITAIN,
Hutchins, Henry Edward. Tetney House, near Grimaby, Lincolnshire Ingall, W. T. F. Mm Greenhithe, Kent
Jay, R. C., 54, Alexandra Road, Cambridge Garden*, Kilbum, w.
Jennings, William, F.R.G.S., 13, Victoria Street
Kitson, James, Elmete Hall. Leeds
Krueger, W. G., Downeville, Sierra County, California
Latham, Baldwin, C.E., 7. Westminster Chambers
Le Feuvre, Wm. H., C.E., F.R.G.S., St. Antholin’s Chambers,
26, Budge Row, Cannon Street, E-C. ; of the Council Lindsay, Lord, 47, Brook Street, w.
Londonderry, the Marquis of, Holdemesse House, Park Lane Longridge, James A., C.E., 3, Westminster Chambers Ludeke, J. Ernst F., 15, Wilmot Place, N.w.
Macdonald, Colonel, Assistant Adjutant-General, Dover Marriott, Frederick, San Francisco, California Matthews, Edwin, 68, Lincoln’s Inn Fields Maxwell, Captain R. J., Army and Navy Club, s.w.
Michaels, J. Porter, Christinen Gasse, No. 4, Kolowratring, Vienna
Moilliet, J. Keir, Bishop’s Frome, Bromyard
Morrieson, Colonel R., Oriental Club
Moy, Thomas, 1, Cliflnrd’s Inn, and 37, Farringdon Street
Mulliner, ft; 59, Great Charlotte Street, Liverpool
Murray, Captain R.N., Murraythwaite, Ecclefechan, N.B,
Nees, Christopher, Telegraph Director, Elsinore, Denmark
Newman, Frederick, C.E., 51, Belsize Road
Norman, J. Musgeove, 15, Old Jewry Chambers
Ohren, Magnus, Lower Sydenham ; of the Council
Osler, Abraham Follett, F.R.S., Birmingham
Perigal, Henry, Jun., 9, North Crescent, Bedford Square
Phillips, W. H., Cemetery Road, Nunhead
Procter, J., Old Castle Buildings, Preeson's Row, Liverpool
Reeves, Thomas, 16, Burton Street, Pimlico
Risley, J. B., C.E., Brondeg, Ferryside, South Wales
Roberts, Major H. C., 48, Hereford Road, Bayswater
Rumble, E. L., A.S.E., 12, Maismore Square
Rumble, Fred. Ireland, 9, Bridge Terrace, Harrow Road
86
AERONAUTICAL SOCIETY.
Satrustequi, Don Joaquin Marcos de, Consul General de Espafia, 21, Billiter Street
Senegal, P., 95, High Street, Kensington Shill, RiCHArD E., 37, Farringdon Street
Siemens, C. W., C.E., F.R.S., 3, Great George Street, Westminster; of the Council
Spencer, Charles, Dungannon Cottage, Knightabridge Barracks Strinofellow, John, Chard, Somerset
Sutherland, His Grace the Duke of ; Vice-President of the Council Sztrma, The Rev. W. S. Sach, St. Augustine’s College, Canteroury Tolme, J. H., C.E., 9, Victoria Street, Westminster Tract, The Honourable Henry Hanburt, Gregynog Newtown, Mont¬ gomeryshire
Walker, Thomas, 24, Oxford Street, Birmingham Wenham, F. H., C. E., F. R. M. S., Padnall Hall, Chadwell, Essex; of the Council
Wright, Henry, Stafford House, St. James’; of the Council Yorke, Pierce Wynne, Dyflryn Aled, Abergele YOUNG, E. W., C.E., 8, New Street, Spring Gardens
PRESENTED BY THE COMMISSIONERS
THE FOLLOWING
SPECIFICATIONS OF PATENTS.
Date. No. Subject. Patentee.
1872 411 An Aerial Machine . D. S. Brown
„ 821 A new or improved Balloon Locomo- Matthew Augustus
tive, or Navigable Balloon . ) TouL
„ 3076 A new system of manageable Balloon ) j> pt;gte
called Duthu’s system, applicable / Duthu to the management of Balloons ... )
(Bigbtl) f. mural Report
OF THE
AERONAUTICAL SOCIETY
OF
GREAT BRITAIN.
IFOIR THE NT EAR 1873.
PRINTED BT
HENRY S. RICHARDSON,
GBKENWIOH.
He \irielin-eil noil pii iih'il photol Illin off net for I’ktk.k Mckkay Hill (Publishers) Ltd.
7:5 sloank Avenue London s.\V.:5 1 !)5B
Hu per minx inn of the Roi/ol Aeronautical 'iorielii
M A I > K A.\l> I’ll! NTKI> IN' till It AT lililTAIN IIV H. It. 1111. 1. MAN .V SONS I.TII.. HtoMK
THE
AERONAUTICAL SOCIETY OF GREAT BRITAIN.
President,
HIS GRACE THE DUKE OF ARGYLL, K T. Utcf-IDrcatljcnts,
HIS GRACE THE DUKE OF SUTHERLAND. RIGHT HON. THE EARL OF DUFFERIN.
LORD RICHARD. GROSVENOR, M.P.
f^onorarg Secretary,
FRED. W. BREAREY, Esq.
f^onorarg Solicitors,
Messrs. MATTHEWS & GREETHAM, 26, Bedford Row, w.o.
Council,
A. ALEXANDER, Esq., C.E., M.A., Sheffield.
FRED. W. BREAREY, Esq., Maidenstone Hill, Blaekheath, S.E. Sir CHAS. T. BRIGHT, F.R.A.S., 26, Duke St., Westminster, S W. CHARLES BROOKE, Esq., M.A., F.R.S., 16, Fitzroy Square, w. JOHN BROWNING, Esq., F.R.A.S., F. R.M.S., 111, Minories, and S3, Strand.
HUGH W. DIAMOND, Esq., M.D., F.S.A., Twickenham. JAMES GLAISHER, Esq., F.R.S., F R.A.S., Blaekheath. Rear-Admiral Lord JOHN HAY, C.B., 149, Piccadilly.
W. H LE FEUVRE, Esq., C.E., F.R.G.S., 28, Brunswick Gardens, w. MAGNUS OHREN, Esq., A.I.C.E., F.C.S., Lower Sydenham, s.E. Lord LINDSAY, 47, Brook Street, w.
F. H. WENHAM, Esq., C.E., Y.P.R.M.S., Padnall Hall, Chad well,.
Essex.
HENRY WRIGHT, Esq., Stafford House, St. James’.
WITH POWLR TO ADD TO THIIB NVMBFR.
Member’s Subscription, £l.ls. per annum, c’atii g fr< n. ti e dry of Election.
Ladies may become Associates upon the same terms.
(STnjFjtfj Annual
OF THE
AERONAUTICAL SOCIETY OF GREAT BRITAIN,
FOR THE YEAR 1873,
Containing an Account of the Proceedings, and a Selection from the Papers and Communications received by the Society during the year, with concluding Remarks upon the present state of the Science.
The Annual General Meeting of Members of this Society was held in the Rooms of the Society of Arts, on Monday Evening, the 30th of June, 1873. Mr. Jamks Glaisher, F.R S., presided. Several models and specimens of apparatus were on the tables, and were exhibited in the course of the evening.
The Chairman, in commencing the business of the Meeting, said: Ladies and Gentlemen, — We meet again hopefully, as we have met on previous occasions. We have to speak to-night, I think, of some progress; our progress has been for some years very slow indeed. 'Whether it has been much accelerated during the past yrar I cannot say, but still I think a decided improvement has been effected. It has been a year distinguished from previous years by experi¬ ments, and it is to experiments we must look for any ultimate success that may attend our efforts. As I have before said, those experiments that are essentially necessary and strictly applicable to aeronautical navigatiou have this great
6
AEEOIf Atm CAL SOCIETY
advantage — that, even should we not succeed in our hopes, our knowledge is increased in the direction required, and in a direction which may be useful in providing for the wants i>{ man Therefore I have urged the continuance of these experiments, because good must follow from them though the ultimate object may or may not be attained.
Perhaps I may be permitted to say a few words on some of the attempts that were made last year. In the order of time that of M. Dupuy tie, Lame should be first noticed. M. de Lome attempts to cause a balloon to deviate from the direction in which the wind blows, and his invention is one to which some attention should be paid. Two conditions, he said, must be complied with in order to achieve his purpose. The first is the permanence of form of balloon ; and the second is that the least resistance should be in a direction parallel to the propelling force. The weight of the balloon in which he