January 30, 1896J 



NATURE 



301 



;irea without adding to the breadth of the machine, they 

 would decrease very considerably the difificulties, referred 

 to above, with respect to the management of the centre of 

 j,^ravity. 



On this principle, Otto Lilienthal constructed his new 

 double-apparatus (F'ig. i), the appearance of which will 

 be noticed from the accompanying illustrations. Each 

 separate surface has an area of nine square metres ; thus 

 he is able to employ the very large carrying surface of 

 eighteen square metres with a breadth of only five and 

 a half metres. The upper surface, which is placed at a 

 distance of about three-quarters of a wing-breadth above 

 the lower, proves in no way a disturbing factor in the 

 machine, as might at first be supposed, but develops 

 simply a vertical lifting force. It may be remarked that 

 this double-surface machine is managed in exactly the 

 same way as the single-framed one. 



From Fig. 2 it is easy to obtain a good idea of 

 the arrangement adopted, by which the upper surface is 

 fixed rigidly to the lower one by means of two rigid 

 stays, the whole surface being held in position by means 

 of thin wires. 



With this new apparatus, Otto Lilienthal has already 

 found that a step in the right direc- 

 tion has been made. The energetic 

 movement of the centre of gravity, 

 and the consequent more safe man- 

 agement of the apparatus, has led 

 him to practise in winds blowing at 

 times over ten metres per second. 

 "These experiments," he says, 

 "have given the most interesting 

 results that I have arrived at since 

 I began." With a wind velocity of 

 six to seven metres per second, the 

 sailing surface of eighteen square 

 metres carried him against the wind 

 in nearly a horizontal direction from 

 the top of the hill, without even 

 having to run at the start, as is 

 generally necessary. More interest- 

 ing still, is it to learn that, with 

 stronger winds, he allows himself to 

 be simply lifted by the wind from 

 the hill-top, and sail slowly against 

 it. Fig. 3 is such a case in point. 

 The same illustration also shows 

 how strong at times may be the side- 

 motion, the operator having to con- 

 siderably alter the position of his 

 centre of gravity to retain his equili- 

 brium. 



As experiments have shown, the sailing path is directed 

 strongly upwards by increasing wind force, and this fact 

 causes him sometimes to be higher in the air than he 

 was at his original starting-point. In this position his 

 apparatus has occasionally come to a standstill ; and this 

 leads him to make the following interesting statement : 

 " At these times I feel ver)' certain that, if I leaned a 

 little to one side, and so described a circle, and further 

 partook of the motion of the lifting air around me, I 

 should sustain my position. The wind itself tends to 

 direct this motion ; but then it must be remernbered that 

 my chief object in the air is to overcome this tendency 

 of turning to the left or right, because I know that behind 

 and under me lies the hill from which I have started, 

 and with which I would come in rough contact if I allowed 

 myself to attempt this circle sailing. I have, however, 

 made up my mind, by means of either a stronger wind or 

 by flapping the wings, to get higher up and further away 

 from the hill, so that, sailing round in circles, I can follow 

 the strong uplifting currents, and have sufficient air space 

 under and about me to complete with safety a circle, 



NO. 1370, VOL. 53] 



and, lastly, to come up against the wind again to 

 land." 



It may be remembered that Lilienthal has previously 

 employed some mechanical aid, such as the flapping of the 

 wings : an illustration of the apparatus so arranged was 

 given in the article already referred to above (Nature, 

 vol. li. p. 178). Perhaps he will apply the same arrange- 

 ment to the lower framework of his present apparatus, 

 and thus accomplish the end he is wishing to attain. 



One can quite understand that sailing against the wind 

 is one thing, and with it another. In the latter case, 

 since the framework is inclined slightly upwards in the 

 direction of motion, the wind would meet the sailing 

 surface from above and shoot the operator, arrow-like, to 

 the ground if he were unable to come up again quick 

 enough to the wind. That such circle sailing will be most 

 probably successfully accomplished by Herr Lilienthal 

 seems certain, but the first few attempts may prove, 

 perhaps, rather rough. 



The recent experience of Otto Lilienthal has thus shown 

 that by means of his new apparatus a very close 

 approximation to flying has been attained. 



Should he, however, find that the accomplishment of 



Fig. 3. 



circling is not attended by any great difficulty, and there 

 appears no reason why it should, then there seems no 

 doubt that an important step will have been made, and 

 the future development of this Fliegesport will depend 

 nearly directly on the Fliegepraxis. 



It is interesting to notice that in America this Lilienthal- 

 method is about to be tested. We have in the British 

 Isles already a follower in Percy S. Pilcher, of Glasgow 

 University, but his experiments at Cardross, in Dum- 

 bartonshire, have not as yet proved very successful, 

 owing to the wings of his apparatus being too much in- 

 clined. He is, however, busy with the construction of a 

 new machine, which will have a sail-area of 300 square 

 feet (= 27-6 square metres). The experience of Lilien- 

 I thai has shown, however, that with such a large expanse 

 i this machine will only be able to be used in moderate 

 ! winds with safety. If its construction be not already too 

 ! far advanced, it would seem advisable to add the second 

 j or upper surface, since its presence has been shown to be 

 I attended by greater stability and easier management of 

 j the whole apparatus. W. J. S, L 



