ARE MEN TO FLY ? T HE symbolical present sent of
old by the Scythian: to Darius, son of Hystaspes, was interpreted to signify that unless his men could swim through the water like the fish, or burrow through the ground like the mole, or fly through the air like the bird, they should perish by the Scythian arrows. Two of the expedients deemed impracticable by the Scythians have been rendered possible by the skill of modern mechanicians and engineers. Men can now urge their way- through the waves of ocean without waiting for favourable winds ; they have long since learned to tunnel through hills, and have now achieved the task of piercing their way through the mighty Alps ; is the time approaching when the third of the paths indicated to Darius by the Scythians will be traversed by daring nien ? We speak of something more, of course, than of mere aerial voyaging by means of balloons, for the balloonist does not pursue his own course, but is simply carried along by the air ; the wind bloweth (him) where it listeth, and not where, if he had the power, he might prefer to travel. The great pro- blem which the aerial voyager has to solve, is to learn how to direct his path through the air as the captain of a steamship selects the course on which he will proceed, or as the birds direct their path when migrating on the approach of winter. Are we to sup- pose that men will presently be able to accomplish this feat ? It would seem at least that scientific men consider the feat to be possible ; for an Aeronautical Society has now been for several years in existence, and in its ranks are many well-known men of science, while its president, Mr. Glaisher, is well known not only as a man of science, but as an aeronaut of some experience. It is also worthy of notice that mechanicians no longer despair (as lately) of mastering the serious mechanical difficulties involved by the problem. They not only believe flight to be possible, but give sufficient evidence in support of their opinion.
Most of us, in considering the question whether men can fly, are attracted rather by the thought of flying singly, as birds fly, than of being borne through the air by aerial machines capable of carrying many persons at a time. So far as the practical aspect of the question is considered, the flight of a man through the air, though it would excite much wonder and admiration, would be scarcely worth the trouble and the risk ; whereas if aerial machines could be constructed whereby long voyages could be safely under- taken, it cannot bo doubted that a really important problem in locomotion would have been solved. It would be something to be able to travel without roads, something to have a highway more silent than the river or the ocean ; but the real value Of aerial travelling would be found in its enforced rapidity. For it is
recognized more and more clearly, as researches are extended, that the supporting power which the air undoubtedly possesses depends chiefly on the velocity with which the air is traversed.
It is indeed a somewhat strange circumstance that hitherto so little attention should have been paid to the significant teaching of the storm. Sir John Herschel tells us that air moving in the hurricane at the rate of ninety-two miles per hour " produces universal desolation, sweeping away buildings and tearing up trees." The same force which can thus whirl the solid materials of buildings through the air is capable beyond question of support- ng contrivances specially adapted for aerial navigation. But in what respects does the air in a hurricane differ from still air save in its rapid motion ? and what difference can there be in the sup- porting power of the hurricane air and the supporting power of still air, when this latter power is called into action by rapid motion through it ? The boy with hia toy kite can answer this queetiou for us ; for in calm weather he can, by running, cause his kite to rise as steadily as though wind were blowing. But the bird answers the question still more satisfactorily ; for the same bird which in calm weather can only secure aerial support by flying swiftly, may bo watched in the storm resting on almost un- moving wings upon the support furnished by the moving air. If we can only urge aerial machines through the air at the rate of seventy or eighty miles per hour—no matter how this velocity is obtained at starting—we need not fear that either the supporting power of the air will be unequal to the task of sustaining the machine, or that there will be any insuperable difficulties in maintaining or increasing that velocity.
We hear, indeed, a great deal about the wonderful strength of girds: and more particularly of the strength of those muscles (the pectoral muscles) by which their wings are worked. But without entering into a consideration of certain fallacies connected with this subject, it will be noticed by any one who carefully studies the motions of birds that flight is often sustained for a considerable interval of time without any effort whatever,—the wings remain- ing absolutely motionless. Of course the pectoral muscles are all the while in action, to maintain the spread of the wings ; but this statical energy is surely not such as the aeronaut need despair of imitating, so long as " struts and braces" aro available. Darwin tells us that oven in the upper regions of the air, near the summits of the Andes, vultures may be seen floating onwards for miles upon motionless wings. What is the secret of this floatation ? Gravita- tion acts as forcibly on the substance of the bird as on that of the animal. Nor can wo believe that there is any buoyancy, properly so called, in the bird's body or wings. Those, indeed, who mis- understand the action of the gas which supports a balloon, and imagine that hydrogen has some inherent capacity for raising heavy bodies, might imagine that a sufficiently large quantity of that or some other gas compressed within the body of the bird might give this mysterious power of floatation (for the pheno- menon witnessed by Darwin is undoubtedly perplexing). But it need scarcely be said that it cannot be in this way that the bird floats. The rarest hydrogen has a much greater raising power than the most compressed ; and a space equal to the whole content of a bird's body, if filled with the rarest hydrogen, and near the sea level, where the air is densest, would not be equal to the support of a tithe of the bird's weight.
It was well remarked at the last meeting of the Aeronautical Society, that Darwin's observation must be regarded as having a most important bearing on the question whether aerial navigation is possible. No explanation was then offered, and indeed the phenomenon was dismissed as an inscrutable mystery. Yet it is to the see mingly inscrutable mysteries of nature that the student of science should look most hopefully for instruction. We believe that Darwin's observation can be explained, and that the explana- tion affords promising evidence in favour of the feasibility of flight. Those vultures which seemed to float steadily through still air must have received support from the air in one or more of three several ways. Either by swift motion acquired before the floating began, and but slowly reduced through the effects of aerial resistance; or by the action of aerial currents through which they were carried ; or else, while seeming to float horizontally, they were in reality traversing a slightly sloped descending path. Neither of the two former explanations seems available, because the floating motion was continued so long that the frictional resistance of the air would almost certainly have destroyed a large share of the original motion through the air. This would equally happen whether the bird had in the first place urged its way swiftly through still air, or had floated itself off, so to speak, upon a swiftly moving air-current. On the other hand, there would seem to be no valid I objection against the third explanation ; for a single observer, at rest, would have no means of determining whether a bird were sailing along horizontally or gliding down a gentle incline. But it matters little which explanation of the three we accept as the most plausible. The point to be chiefly noticed is the fact that a heavy body—for the vulture is no chicken, so to speak—can be sustained for long distances merely by the supporting action of the air. There can be little doubt that it is only on account of the perfect steadiness of their motion through the air that they are thus supported. The efforts of aeronautical mechanicians must be directed to secure a similar steadiness of motion for aerial machines. Granted this, there can be no reason why the powers of steam and iron should not avail to secure an aerial motion even surpassing in rapidity the flight of the swiftest birds. Unless we are willing to believe that birds fly by some power • distinct from any which physical science deals with, we seem justified in believing that the bird may be matched or surpassed by the flying-machine as surely as the swiftest animals are surpassed by the locomotive. It is en- couraging to consider that the actual amount of power necessary to convey a weight through the air (if support is derived directly from the air), is very much less than that required to convey the same weight by sea or by land. In the presence of failing coal- supplies, this consideration will one day assume first-rate. importan ce.
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