ly we have to inquire whether the air may not resist descent so strongly that with comparatively small effort a horizontal or even ascending motion may be effected. A familiar illustration of this supporting power of the atmosphere is given in the flight of an oyster-shell or piece of thin slate, deftly thrown from a schoolboy's practised hand. Such a missile, instead of following the parabolic path traversed by an ordinary projectile, is seen to skim along almost like a bird on resting pinions. It will sometimes even ascend (after the projectile force has ceased to act in raising it), as though in utter disobedience to the laws of gravitation.

The fact appears to be, that when a horizontal plane traverses the air in a horizontal direction, the supporting power of the air is increased in proportion as the plane moves more quickly, or in proportion to the actual quantity of air it glides over, so to speak. Indeed we have clear evidence to this effect in the behavior of the common toy-kife, the supporting power of which is increased in proportion to the force of the wind. For a kite, held by a string in a strong horizontal current of air, corresponds exactly to an inclined plane surface drawn swiftly in a horizontal direction during a calm. The same supporting power which results from the rapid passage of the air under the kite will be obtained during the rapid passage of the kite over still air.

When we study the flight of birds, we we are confirmed in the opinion that velocity of horizontal motion is a point of extreme importance as respects the power of flying. For though there are some birds which seem to rise almost straight from the ground, yet nearly all, and especially the larger and heavier birds, have to acquire a considerable horizontal velocity before they can take long flights. Even many of those birds which seem, when taking flight, to trust rather to the upward and downward motion of their wings than to swift horizontal motion, will be found, when carefully observed, to move their wings up and down in such sort as to secure a rapid forward motion. The present writer has been much struck by the singularly rapid forward motion which pigeons acquire by what appears like a simple beating of their wings. A pigeon which is about to fly from level ground may be seen to beat its wings

quickly and with great power; and yet instead of rising with each downward stroke, the bird is seen to move quite horizontally, as though the wings acted like screw-propellers. We believe, in fact, that the wings during this action do really act, both in the upward and downward motion, in a manner resembling either screwpropulsion or the action by which seamen urge a boat forward by means of a single oar over the stern.* The action of a fish's tail is not dissimilar; and as the fish, by what seems like a simple beating of its tail from side to side, is able to dart swiftly forwards, so the bird, by what seems like a beating of its wings up and down, is able --when occasion requires-to acquire a swift forward motion. At the same time it must be understood that we are not questioning the undoubted fact that the downward beat of a bird's wing is also capable of giving an upward motion to the bird's body. The point to be specially noticed is that when a bird is taking flight from level ground, the wings are so used that the downward stroke gives no perceptible upward motion.

But since a horizontal velocity is thus effective, we might be led to infer that the larger flying creatures, which, cæteris paribus, travel more swiftly through the air than the smaller, would require a smaller relative extent of supporting surface. We are thus led to the consideration of that point which has always been regarded as the great, or rather the insuperable difficulty, in the way of man's attempts at flight,-his capacity or incapacity to carry the requisite extent of supporting surface. We are led to inquire whether a smaller extent of supporting surface than has hitherto been deemed necessary may not suffice in the case of a man, and à fortiori in the case of a large and powerful flying-machine.

The inference to which we have thus been led, is found to accord perfeetly with the observations which have been made upon flying creatures of different dimensions. It has been found that the supporting surface of these creatures,whether insects, birds, or bats,-by no means varies in proportion to their weight. This is one of the most important results to

*Sailors call this sculling, a term more com

monly applied to the propulsion of a boat by a single oarsman using a pair of oars, or sculls.

which the recent inquiries into the problem of flight have led; and we believe that our readers cannot fail to be interested by an account of the relations which have been observed to hold between the weight and the supporting surface of different winged creatures.

We owe to M. de Lucy, of Paris, the results of the first actual experiments carried out in this direction. The following account of his observations (made in the years 1868, 1869) is taken from a paper by Mr. Brearey, the Honorary Secretary to the Aeronautical Society. "M. de Lucy asserts," says Mr. Brearey, "that there is an unchangeable law to which he has never found any exception, amongst the considerable number of birds and insects, whose weight and measurements he has taken, viz., that the smaller and lighter the winged animal is, the greater is the comparative extent of supporting surface. Thus, in comparing insects with one another, the gnat, which weighs 460 times less than the stag-beetle, has 14 times greater relative surface. The lady-bird, which weighs 150 times less than the stag-beetle, possesses 5 times more relative surface, etc. It is the same with birds. The sparrow, which weighs about ten times less than the pigeon, has twice as much relative surface. The pigeon which weighs about eight times less than the stork, has twice as much relative surface. The sparrow, which weighs 339 times less than the Australian crane, possesses 7 times more relative surface, etc. If we now compare the insects and the birds, the gradation will become even more striking. The gnat, for example, which weighs 97,000 times less than the pigeon, has 40 times more relative surface; it weighs 3,000,000 times less than the crane of Australia, and possesses relatively 140 times more surface than this latter, which is the heaviest bird M. de Lucy had weighed, and was that also which had the smallest amount of surface, the weight being nearly 21 lbs., and the supporting surface 139 inches per kilogramme (2 lbs. 3 oz.). Yet of all travelling birds the Australian cranes undertake the longest and most remote journeys, and, with the "exception of the eagles, elevate themselves highest, and maintain flight the longest."

M. de Lucy does not seem to have noticed the law to which these numbers

point. It is exceedingly simple, and amounts in fact merely to this, that instead of the wing-surface of a flying creature being proportioned to the weight, it should be proportioned to the surface of the body (or technically, that instead of being proportioned to the cube, it should be proportioned to the square of the linear dimensions). Thus, suppose that of two flying creatures one is 7 times as tall as the other, the proportions of their bodies being similar, then the body-surface of the larger will be 49 times (or 7 times 7) that of the other, and the weight 343 times (or 7 times 7 times 7) that of the other. But instead of the extent of wing-surface being 343 times as great, it is but 49 times as great. In other words, relatively to its weight the smaller will have a wing-surface 7 times greater than that of the larger. How closely this agrees with what is observed in nature, will be seen by the case of the sparrow as compared with the Australian crane; for M. de Lucy's experiments show that the sparrow weighs 339 times less than the Australian crane, but has a relative wing-surface 7 times greater.

It follows, in fact, from M. de Lucy's experiments that, as we see in nature, birds of similar shape should have wings similarly proportioned, and not wings corresponding to the relative weight of the birds. The same remark applies to insects; and we see, in fact, that the bee, the bluebottle, and the common fly-insects not unlike in their proportionshave wings proportioned to their surface dimensions; the same holding amongst long-bodied insects, like the gnat and the dragon-fly, and the same also among the different orders of flying beetles.

So that, setting apart differences of muscular capacity and adaptation, a man, in order to fly, would need wings bearing the same proportion to his body as we observe in the wings of the sparrow or the pigeon. In fact, the wings commonly assigned to angels by sculptors and painters would not be so disproportioned to the requirements of flight as has been commonly supposed, if only the muscular power of the human frame were well adapted to act upon wings so placed and shaped, and there were no actual inferiority in the power of human muscles (crosssection for cross section) as compared with those of birds.

So far as the practicability of actual

flight on man's part is concerned, these two points are, indeed, among the most important that we have to consider. It was to Borelli's remarks on these points, in his famous treatise, De Motu Animalium, that the opinion so long entertained respecting the impracticability of flight must be referred. He compared the relative dimensions of the breast-muscles of birds with those of the corresponding muscles in man, and thence argued that man's frame is altogether unadapted to the use of wings. He compared also the relative muscular energy of birds and men, that is, the power of muscles of equal size in the bird and the man; and was yet further confirmed in the opinion that man can never be a flying animal.

But although the reasoning of Borelli suffices perfectly well to show that man can never fly by attaching pinions to his arins, and flapping these in imitation (however close) of a bird's action in flying, it by no means follows that man must be unable to fly when the most powerful muscles of his body are called into action to move suitably-devised pinions. M. Besnier made a step in this direction (towards the close of the last century) when he employed, in his attempts to fly, those powerful muscles of the arm which are used in supporting a weight over the shoulder (as when a bricklayer carries a hod, or when a countryman carries a load of hay with a pitchfork). But the way in which he employed the muscles of the leg was less satisfactory. In his method, a long rod passed over each shoulder, folding pinions being attached to both ends. of each rod. When either end of a rod was drawn down, the descending pinion opened, the ascending pinion at the other end closing; and the two rods were worked by alternate downward pulls with the arms and legs. The downward pull with the arms was exceedingly effective; but the downward pull with the legs was altogether feeble. For the body lying horizontally, the muscles used in the downward pull with the legs were those by which the leg is carried forward in walk ing, and these muscles have very little strength, as any one will see who, standing upright on one leg, tries, without bending the knee of the other, to push forward any considerable weight with the front of this leg.

Yet even with this imperfect contrivance

His

Besnier achieved a partial success. pinions did not, indeed, serve to raise him in the air; but when, by a sharp run forward, he had brought that aërial supporting power into action of which we have spoken above, the pinions, sharply worked, so far sustained him as to allow him to cross a river of considerable width. It is not unlikely that, had Besnier provided fixed sustaining surfaces, in addition to the movable pinions, he might have increased the distance he could traverse. But, as regards flight, there was a further and much more serious defect in his apparatus. No means whatever were provided for propulsion. The wings tended to raise the body (this tendency only availing, however, to sustain it); but they could give no forward motion. With a slight modification, it is probable that Besnier's method would enable an active man to travel over ground with extreme rapidity, clearing impediments of considerable height, and taking tolerably wide rivers almost "in his stride"; but we believe that the method could never enable men actually to fly.

It may be remarked, indeed, that the art of flying, if it is ever attained, will probably be arrived at by means of attempts directed, in the first place, towards rapid passage along terra firma. As the trapeze gymnast avails himself of the supporting power of ropes, so the supporting power of the air may be called into action to aid men in traversing the ground. The following passage from Turnor's Astra Castra shows that our velocipedists might soon be outvied by half-flying pedestrians:

"Soon after Bacon's time," he tells us, "projects were instituted to train up children from their infancy in the exercise of flying with artificial wings, which seemed to be the favorite plan of the artists and philosophers of that day. If we credit the accounts of some of these experiments, it would seem that considerable progress was made that way. The individuals who used the wings could skim over the surface of the earth with a great deal of ease and celerity. This was accomplished by the combined faculties of running and flying. It is stated that, by an alternate continued motion of the wings against the air, and the feet against the ground, they were enabled to move along with a striding motion, and with incredible speed."

A gymnast of our own day, Mr. Charles

Spencer ("one of the best teachers of gymnastics in this country," says Mr. Brearey), has met with even more marked success, for he has been able to raise himself by the action of wings attached to his arms. The material of which these wings were made was too fragile for actual flight; and Mr. Spencer was prevented from making strong efforts because the wicker-work to which the apparatus was attached, fitting tightly round his body, caused pain, and obstructed his movements. Yet he tells us that, running down a small incline in the open air, and jumping from the ground, he has been able, by the action of the wings, to sustain flight for a distance of 120 feet; and when the apparatus was suspended in the transept of the Crystal Palace (in the spring of 1868), he was able, as we have said, to raise himself, though only to a slight extent, by the action of the wings. It should be remarked, however, that his apparatus seems very little adapted for its purpose, since the wings are attached to the arms in such sort that the weak breast-muscles are chiefly called into play. Borelli's main objection applies in full to such a contrivance; and the wonder is that Mr. Spencer met with even a partial success. One would have expected rather that the prediction of a writer in The Times (calling himself Apteryx, or the Wingless) would have been fulfilled, and that "the aeronaut, if he flapped at all, would come to grief, like the sage in Rasselas, and al! others who have tried flying with artificial wings."

The objection founded on the relative weakness of the muscles of man as compared with those of birds (without reference to the question of adaptation), seems at first sight more serious. Although there can be little question that the superior strength of the muscles of birds has been in general enormously exaggerated, yet such a superiority undoubtedly exists to some degree. This gives the bird a clear advantage over man, insomuch that man can never hope by his unaided exertions to rival the bird in its own element. It by no means follows, however, that because man may never be able to rival the flight of the eagle or the condor, of the pigeon or the swallow, he must therefore needs be unable to fly at all.

It should be remembered, also, that men can avail themselves of contrivances

by which a considerable velocity may be acquired at starting; and that when the aëronaut is once launched with adequate velocity, a comparatively moderate exertion of force may probably enable him to maintain that velocity, or even to increase it. In this case, a moderate exertion of force would also suffice to enable him to rise to a higher level. To show that this is so, we need only return to the illustration drawn from the kite. If a weight be attached to a kite's tail, the kite, which will maintain a certain height when the wind is blowing with a certain degree of force, will rise to a greater height when the force of the wind is but slightly increased.

Kites afford, indeed, the most striking evidence of the elevating power resulting from the swift motion of an inclined plane through the air, the fact being remembered always that, whatever supporting and elevating power is obtained when air moves horizontally with a certain velocity against an inclined plane, precisely the same supporting and elevating power will be obtained when the inclined plane is drawn or propelled horizontally with equal velocity through still air. Now the following passages from the History of the Charvolant, or kite-carriage, bear significantly on the subject we are now upon. The kite employed in the first experiments (made early in the present century) had a surface of fifty-five square feet. "Nor was less progress made in the experimental department when large weights were required to be raised or transposed. While on this subject, we must not omit to observe that the first person who soared aloft in the air by this invention was a lady, whose courage would not be denied this test of its strength. An arm-chair was brought on the ground, then, lowering the cordage of the kite by slackening the lower brace, the chair was firmly lashed to the main-line, and the lady took her seat. The main-brace being hauled taut, the huge buoyant sail rose aloft with its fair burden, continuing to ascend to the height of a hundred yards. On descending, she expressed herself much pleased with the easy motion of the kite and the delightful prospect she had enjoyed. Soon after this, another experiment of a similar nature took place, when the inventor's son successfully carried out a design not less safe than bold-that of scaling by

this powerful aërial machine the, brow of a cliff two hundred feet in perpendicular height. Here, after safely landing, he again took his seat in a chair expressly prepared for the purpose, and, detaching the swivel-line which kept it at its elevation, glided gently down the cordage to the hand of the director. The buoyant sail employed on this occasion was thirty feet in height, and had a proportionate spread of canvass. The rise of the machine was most majestic, and nothing could surpass the steadiness with which it was manoeuvred, the certainty with which it answered the action of the braces, and the ease with which its power was lessened or increased. . . . Subsequently to this, an experiment of a very bold and novel character was made upon an extensive down, where a wagon with a considerable load was drawn along, whilst this huge machine at the same time carried an observer aloft in the air, realizing almost the romance of flying."

We have here abundant evidence of the supporting and elevating power of the air. This power is, however, in a sense, dormant. It requires to be called into action by suitable contrivances. In the kite, advantage is taken of the motion of the air. In flight, advantage must be taken of motion athwart the air, this motion being, in the first place, communicated while the aëronaut or flying-machine is on the ground. Given a sufficient extent of supporting surface and an adequate velocity, any body, however heavy, may be made to rise from the ground; and there can be no question that mechanicians can devise the means of obtaining at least a sufficient velocity of motion to raise either a man or a flyingmachine, provided with no greater extent of supporting surface than would be manageable in either case. It is not the difficulty of obtaining from the air at starting the requisite supporting power that need deter the aëronaut. The real difficulties are those which follow. The velocity of motion must be maintained, and should admit of being increased. There must be the means of increasing the elevation, however slowly. There must be the means of guiding the aëronaut's flight. And, lastly, the aëronaut or the flying-machine must fly with well-preserved balance-the supporting power of the air depending entirely on the steadi

ness with which the supporting surfaces traverse it.

We believe that these difficulties are not insuperable; and not only so, but that none of the failures recorded during the long history of aëronautical experiments need discourage us from trusting in eventual success. Nearly all those failures have resulted from the neglect of conditions which have now been shown to be essential to the solution of the problem. Nothing but failure could be looked for from the attempts hitherto made; and indeed, the only wonder is that failure has not been always as disastrous as in the case of Cocking's ill-judged descent. If a man who has made no previous experi ments will insist on jumping from the summit of a steeple, with untried wings attached to his arms, it cannot greatly be wondered at that he falls to the ground and breaks his limbs, as Allard and others have done. If, notwithstanding the wellknown weakness of the human breastmuscles, the aëronaut tries to rise by flapping wings like a bird's, we cannot be surprised that he should fail in his purpose. Nor again can we wonder if attempts to direct balloons from the car should fail, when we know that the car could not even be drawn with ropes against a steady breeze without injury to the supporting balloon. And we need look no further for the cause of the repeated failures of all the flying-machines yet constructed, than to the fact that no adequate provision has yet been made to balance such machines, so that they may travel steadily through the air. It seems to have been supposed that if propelling and elevating power were supplied, the flying-machine would balance itself; and accordingly, if we examine the proposed constructions, we find that in nine cases out of ten (if not in all) the machine would be as likely to travel bottom-upwards as on an even keel. The common parachute (which, however, is not a flying-machine) is the only instance we can think of in which a non-buoyant machine for aërial locomotion has possessed what is called 66 a position of rest."

Perhaps the gravest mistake of all is that of supposing that, on a first trial, a man could balance himself in the air by means of wings. Placed, for the first time, in deep water, man is utterly unable to swim, and if left to himself will inevita