December :o, i Sqj 



NA TURE 



177 



by means of models, patterns, &c., are excellent a^ far as they 

 go, but there seems lo be great need of a systematic course 

 specially designed to lead gradually up to the siudyif deductive 

 geometry. The following books will be fcund useful by 

 teachers who care to give the experimental method a trial : 

 "Paper Folding," by T. Sundara Kow (Addison and Co., 

 Madras) ; " Tnventional Geometry," by W. G. Spei cer (Wil- 

 liams and Norgaie); "Experimental Geometry," by Paul liert 

 (Cassell and Co.) ; " Natural Geometry," by A. Mault (Mac- 

 niillanand Co.); "Geometrical Drawing," by A. J. Pressland 

 (Rivinglon, Percival, and Co.). Tothese may be added some 

 older ones, which n ay occa^'onally be picked up second-hand : 

 Scott Russell's "Geometry in Modern Life," Dupin's " Ma- 

 tbemaiics," and " Conversations on Geonetry " (Anon.). 

 Adelaide Square, Bedford. Edwakd M. Langlev. 



LIUENTHAL'S EXPERIMENTS IN FLYING. 



IN a previous article in Nature (vol. xlix. p. 157) we 

 had occasion to refer to the very interesting experi- 

 ments which were being carried out by Herr Otto 

 Lilienthal with regard to the possibility of human beings 

 being able to acquire the art of flying through the air, 

 more or less, in the fashion of birds. 



These investigations in aerial navigation are con- 

 spicuous from all other attempts of the present day, by 

 their great difference in the method of procedure adoptee). 

 The principle of Maxitii's machine, for instance, is to 

 construct an apparatus to navigate the air by itself, 

 carrying one or more passengers. Every movement 

 of the machine, however, is left to the apparatus itself, 

 and to battle with the difficulty of sustaining its own 

 equilibrium the mechanism must necessarily be most 

 complicated. 



Lilienthal depends for the success of his apparatus on 

 himself, trusting lo his powers of instinct to keep his 

 equilibrium by corresponding movements of his centre of 

 gravity. Man in this case is the main llyer,the apparatus 

 being only an adjunct, and it is from the ability of the 

 former that he expects to obtain positive results. His 

 apparatus is siinple, cheap, and easily constructed ; these 

 are great points, as experiments can be carried on, even 

 at the expense of the loss of a few machines. 



The whole success of aerial tlying can be summed up 

 in the word c'(/iii/ibriii»!, and it is here that the diffi- 

 culty lies. Given a perfectly quiet or very nearly still air, 

 there is no doubt that machines can be constructed so 

 as to soar and travel through the air. This stale of at- 

 mosphere is \ery rare ; but, on the other hand, there are 

 all sorts of disturbances, currents, and wave-motions 

 which render aerial navigation a far greater difficulty 

 than is usually imagined. 



One often envies a bird which, with perfect case, soars 

 above us ; but it must be recollected that it is endowed 

 with a delicate system of nerves which are always on the 

 alert, and answer to any call made on them to sustain 

 equilibrium. These movements are made quite uncon- 

 sciously, and with the loss of the minimum amount of 

 energy. To construct an apparatus that would accom- 

 plish this in an etiicient manner would be simply impos- 

 bible ; but there seems no reason why man should not 

 approximate to it to a certain extent by the help of an 

 appropriate framework. With perseverance and many 

 trials he should be able to master at least some of the 

 rudiments, and eventually make short llights. 



For this leason Herr Lilienthal's experiments must be 

 looked upon as yet only as first attempts, and con- 

 sequently as experiments pure and simple, and expe- 

 rience only will show how far they can be successfully 

 brought. Falls must be expected in the preliminary 

 trials until the operator becomes accustomed 10 the many 

 new conditions which make themselves apparent at 

 every step, before they can be mastered instinctively. 

 Similar ditiiculties have to be contended with when learn- 



ing to ride a bicycle. The beginner is at first unable to 

 keep his equilibrium, and so wobbles here and there, 

 with the loss of much power, until he eventually finds 

 himself hugging the earth. This is simply because he 

 is doing something unusual, and is not accustomed to 

 the new conditions. An adept rider, on the other hand, 

 never thinks of the possibility of falling, and quite un- 

 consciously keeps his equilibrium without any exertion or 



loss of power on his part. So it is with this new sailing 

 machine, and it is only by practice that success can be 

 attained. 



To commence operations the simplest apparatus must 

 be used, and the easiest steps attempted. This is the 

 way Herr Lilienthal began. In his first experiments, 

 with the help of his wing-shaped framework, he made 

 flights from elevated points in calm weather, the lengths 



NO. 13 12, VOL. 51] 



Fig. a. 



of these flights increasing as he gained in experience. 

 Sometimes as many as 500 metres were covered in one 

 bound under satisfactory conditions. 



In his more recent experiments he has been making 

 considerable progress in developing this mode of sailing. 

 Two objects have been kept well in mind : the first, to 

 accomplish that method of- sailing which is adopted by 

 birds which spend hours in the air at a time without ever 



