NATURE 



25 



THURSDAY, MAY 14, 



FLIGHT. 



The Aeronautical Annual, 1S96. Edited by James 

 Means. Medium 8\o, pp. 15S. f Boston : W. B. 

 Clarke and Co. London : \Ym. Wesley and Sons, 

 1S96.) 

 Zur A/ce/iani/c ties Vogcljiugcs. \"on Dr. Fr. Ahlborn. 

 Demy 4to, pp. 134. (Hamburg: L. Friedrichsen and 

 Co., 1896.) 



TILL quite recently, artificial flight was regarded in 

 much the same light as perpetual motion, the 

 philosophers stone, and other insoluble problems. But, 

 now that Maxim, Langley, and others have demonstrated 

 the possibility of overcoming the purely mechanical 

 difficulties of flight, a wide field has been thrown open 

 for scientific research in investigating the laws underlying 

 the flight of birds and their practical appUcation to the 

 flight of man. The present record of investigations per- 

 formed and theories propounded during the past year, 

 will prove of great value to all who are interested in the 

 subject by indicating what work has been done and what 

 still remains undone. 



The "Annual" opens with a long account by Lilienthal 

 of recent experiments performed with his new apparatus, 

 in which two superposed wing surfaces are employed 

 instead of one. A description of these experiments was 

 given in N.'\ture for January 30 ; but it may be interest- 

 ing to call attention to the diagram of the undulating- 

 path of Lilienthal's machine when raised by a sudden 

 head-wind and again allowed to descend. The motion 

 bears a striking resemblance to that of a model glider 

 allowed to descend in still air, although in the latter case 

 the undulatory course is not due to any wind beyond 

 what the glider makes for itself in its descent. 



.•\fter a short editorial note on the analogy between the 

 development of the flying machine and that of the modern 

 bicycle, we have a well-written article by Maxim on 

 "Natural and Artificial Flight." Our interest naturally 

 centres round the sections dealing with the author's 

 experiments on the relative advantages and disadvan- 

 tages of narrow and wide planes. These experiments 

 fully confirm the theory that narrow superposed planes 

 possess greater lifting power per square foot than a single 

 wide plane, a principle which Maxim [proposes to utilise 

 most injyniously in his next machine by constructing 

 his condenser of aeroplanes capable of lifting their own 

 weight + 1000 lb. additional. Maxim, however, doubts 

 whether in an actual machine it may be safe to dispense 

 with wide planes altogether, on account of the risk arising 

 in case of a sudden breakdown. I'ossibly a suitable 

 compromise may result from adoptin;^ the "cellular" 

 principle, which has been introduced with such success in 

 the Hargrave kite. A number of important experiments 

 with this and other kites, notably the " Malay " kite, are 

 described in subsequent articles of the '" .Annual." 



That aerial navigation is regardetl as a subject of 



national importance on the other side of the Atlantic, is 



evidenced by the Bill introduced into the .Senate of 



Washington on December 4, 1895, '" provide for the 



NO. 1385. VOL. 54] 



award of money prizes of 100,000 dols. and 25,000 dols., 

 the first for the successful achievement of mechanical 

 flight, and the second for improvements in soaring 

 machines. The editor of the "Annual" evidently inclines 

 to the view that the final solution of the problem will 

 result from a successful combination of the ingenuity 

 of Lilienthal and Maxim. 



Passing now to the flight of birds, w-e find in the first 

 part of Dr. Ahlborn's memoir a detailed account of the 

 form and structure of birds' wings, and their action in 

 active or "rowing" flight. Marey's observations, in 

 particular, are discussed at some length and freely criti- 

 cised. The second part deals with the so-called soaring 

 of birds — that is, their power of sustaining themselves 

 continuously in the air without flapping their wings ; the 

 term " sailing flight," lately adopted by American writers 

 as a literal translation of the French " vol & voile," is a 

 better name for this action. Unfortunately Dr. Ahlborn's 

 suggested explanation will not bear close examination from 

 a theoretical standpoint. We may take it as an axiomatic 

 consequence of general dynamical principles that when a 

 current of air is blowing uniformly, the relative motion 

 of a bird flying freely is the same as if the current were 

 reduced to rest by applying an equal and opposite 

 velocity both to the air and bird. Starting from this 

 fact. Lord Rayleigh, Prof Langley, and other investi- 

 gators have long realised the impossibility of a bird sup- 

 porting itself without the expenditure of muscular action 

 in a uniform horizontal wind, and they have therefore 

 had to seek other sources of energy, either in the varia- 

 bility of the wind velocity, or in local upward convection 

 or other air currents, of which birds have been sup- 

 posed to take ad\antage. Dr. Ahlborn, however, seems 

 to hold the opinion that these variations are rather 

 a hindrance than a help to the sailing bird, and that the 

 kinetic energy of the wind is the sole source from which 

 the bird derives its energy. To support this view, the 

 author considers the action of a side wind on a bird 

 sailing round and round in a circle, and he derives his 

 supposed gain of energy by arguments which, though 

 ingenious, are not at all convincing. 



The theory of sailing flight is examined from a some- 

 what more plausible standpoint in the " Annual." ALaxim 

 inclines to the view that upward currents of air are the 

 chief cause of the phenomena. Prof. Pickering con- 

 tributes an article first published in 1889, in which he 

 advocates the theory that the action'depends on pulsations 

 or gusts of wind, thus agreeing substantially with the 

 views enunciated subsequently by Prof Langley in his 

 paper on "The Internal Work of the Wind."' Mr. 

 Octave Chanute contributes the first portion of a paper 

 on the subject, but as yet he deals exclusively with 

 observations on sailing birds, and gives no theoretical 

 explanation of their action. We regret that this writer 

 has had to defer till next year's " Annual " his mathe- 

 matical calculations connected with this singular 

 phenomenon. 



With such literature as the " Annual " at hand, the 

 aeronaut should have little difiiculty in deciding what 

 experiments will be the most likely to lead to the 

 realisation of artificial flight. G. H. B. 



' Proceedings of the .-Veronauticil Cung 



1S93. 



c 



