March 28, 1901] 



NA TURE 



527 



designed by Barthelemy Lourenco in Portugal, by the novelist 

 Retif de la Bretonne, by Blanchard, before he became noted as 

 a balloonist, and the prospectus of the Minerva issued by one 

 Robertson when interest in ballooning was at its height. Even 

 in recent times equally absurd devices have been promulgated, 

 such as aerial tramcars supported by cigar-shaped gas vessels, 

 not one-hundredth of the size necessary to raise such loads, and 

 seats in such aerial tramcars with cavities filled with gas whose 

 actual lifting power would amount to a few milligrams, and 

 others. 



The problem of aerial navigation, i.e. of performing directed 

 journeys in the air, made no progress until Montgolfier's invention 

 of the balloon. This rendered it possible to ascend in the air, 

 but did not enable the motion to be directed, and from that time 

 on aeronauts became divided into two classes: those who sought 

 to navigate the air with balloons that rendered their appa- 

 ratus lighter than air, and those who experimented with 

 machines heavier than air but supported on structures re'- 

 sembling wings. 



Balloons have often proved invaluable in times of war, and the 

 war in South Africa has been no exception, thanks partly to the 

 exertions of Major Baden-Powell. But the most practically 

 useful application of the balloon in times of peace was inaugur- 

 ated by Glaisher's ascents into the upper regions of the atmo- 

 sphere for the purpose of obtaining meteorological data, and it 

 is only recently that the balloon has been superseded for this 

 purpose by the kite now largely used in America. 



The experiments of Count von Zeppelin last summer, amount- 

 ing as they did to the performance of a directed journey through 

 the air, in some cases against a head wind, enable us to say that 

 a solution of this problem was obtained before the end of 

 the nineteenth century. The only previous achievement ap- 

 proaching von Zeppelin's was that of Messrs. Renard and Krebs 

 in 1885 with the French war balloon, "La France." These 

 experimenters on one occasion actually succeeded in performing 

 a journey in the air and returning to the starting point ; but as 

 the feat was never repeated and the speed of their balloon is 

 stated by one writer at four and by another at fourteen miles an 

 hour, it is somewhat difficult from such conflicting evidence 

 to estimate the amount of success achieved. The speed at- 

 tained by Count Zeppelin's balloon was about eight metres per 

 second, say seventeen and a half miles an hour, and agreed 

 very closely with that predicted by calculation, viz., 8 "12 

 metres per second. With lighter and more powerful motors 

 Count Zeppelin hopes to increase the speed by 50 per cent. 

 The chief features of this machine are (i) its division into seven- 

 teen compartments, which prevents the gas from collecting at 

 one end or oscillating in the balloon in such a way as to increase 

 the resistance ; (2) the distribution of the load at two points 

 instead of at the centre, which reduces the mechanical difficulty 

 of supporting a heavy weight by a cigar-shaped balloon. 



The subject of dynamical flight without the aid of balloons 

 opens up three fields of study: — (i) experiments on the air- 

 resistance' of planes and curved surfaces, systems of such aero- 

 planes and aerocurves variously arranged, and propellers ; 

 (2) the construction of motors of minimum weight per horse- 

 power, using the sources of energy of minimum weight per foot- 

 pound ; (3) experiments on the balance, stability and control of 

 aeroplanes and aerocurves. A historic retrospect of the work 

 done in the past century includes Captain Le Bris's gliding 

 experiments with his "artificial albatross" in 1854; De 

 Villeneuve's reported feat of raising himself into the air, in 1870, 

 by a machine driven by steam supplied from a flexible hose ; the 

 experiments on air resistance conducted in 187 1 ; Langley's 

 confirmation, in 1891, of Duchemin's formula for the thrust of 

 an oblique current on a plane area, and his proof of the law 

 according to which the horse-power per unit of weight lifted 

 decreases with the speed ; and Phillips's Wealdstone experi- 

 ments on the advantages of narrow superposed planes over wide 

 planes of equal area. 



Coming to the question of horse-power, the chief interest in 

 Sir Hiram Maxim's famous experiments centred round his 

 engine, with which he obtained 362 horse-power, the machine 

 weighing about 8000 lbs. Langley and Hargreave are stated 

 to have designed motors weighing 7 and 10 lbs. per horse- 

 power respectively ; while Da Pra has made theoretical calcu- 

 lations in connection with designs of an aerial machine from 

 which he concludes that such a machine could be made capable 

 of carrying a motor weighing 15 kilograms per horse-power. A 

 more experimental treatment of the question of horse-power is 



NO. 1639, VOL. 63] 



afforded by estimates of the rate at which work is done by 

 gravity in the gliding experiments of Lilienthal, Pilcher and 

 Chanute, from which it appears that about 2 horse- power would 

 be required to support the machines. Mr. Chanute further 

 estimates the possible weight of the motor per horse-power in a 

 one-man machine at 4 lbs. for screws, 8 lbs. for wings, and 14 

 lbs. for aerocurves. 



But the most difficult question connected with the flying 

 machine is its balance and stability under the conditions ordin- 

 arily prevailing in our atmosphere. The very fluctuations of 

 wind velocity which may furnish a source of energy for birds in 

 sailing flight vastly increase the danger of experiments on arti- 

 ficial flight. It is easy to construct a glider which when dropped 

 in a room from any position will right itself and begin to glide 

 before reaching the ground ; but the same glider when let fall 

 from a window will continue to roll over and over and fall to the 

 ground. More than thirty years ago Mr. Wenham made a model 

 which would glide well from a window, but when let fall 

 from a balloon in one of Glaisher's ascents it overturned after 

 descending twelve yards. 



Of the three, Lilienthal, Pilcher and Chanute, who have done 

 most to solve this question of balance and stability, the two first 

 met with fatal accidents just when their experiments were 

 becoming most successful, and we are naturally led to compare 

 their methods with those adopted by Mr. Chanute. 



Both Lilienthal and Pilcher used machines with broad curved 

 wings, the former preferring two superposed aerocurves and the 

 latter adopting a single- surfaced machine. In both machines 

 the wings were rigidly fixed, the operator relying on the move- 

 ments of his body to counteract the effects of any sudden gust of 

 wind tending to overturn the machine. Chanute, on the other 

 hand, experimented with narrow superposed wings, some of his 

 machines having as many as eleven or twelve aerocurves, 

 arranged in pairs. Instead of balancing himself by his own 

 agility, the wings were movable about pivots and were held in 

 position by springs in such a way that their displacements, 

 caused by a sudden gust of wind, gave the machine a tendency 

 to right itself. Finally, a two-surfaced machine with narrow 

 superposed rectangular surfaces, also with automatic balancing 

 arrangements, was devised by Mr. Herring. With this machine, 

 gliding was possible in winds of 31 i miles an hour, the greatest 

 wind velocity in Lilienthal's experiments having been only 22 

 miles an hour, and little practice was required to control the 

 machine. Practically no motions of the body were needed when 

 a gust of wind struck the machine in a fore and aft direction, 

 and but little movement was needed in the case of a side gust. 

 The longest glide was 927 feet, and was performed by " quarter- 

 ing," i.e. sailing parallel to the side of a hill up which the wind 

 was blowing. 



The experiments of Messrs. Chanute and Herring constitute 

 a distinct advance in the construction of gliding machines, and 

 lead us nearer to the possibility of obtaining a true flying machine 

 propelled by a motor. The addition of such a motor, if only by 

 increasing the weight of the apparatus, would largely add to 

 the difficulty of controlling it in the first trials, and the action 

 of the propeller might considerably affect the balance. It is 

 not improbable that after the first start is once made, the motor- 

 driven machine may prove to possess greater steadiness in 

 flight than the present gliders. In the former the thrust of the 

 propeller is fixed relative to the body, in the latter the only 

 motive force, due to gravity, is fixed in space, and Mr. Herring's 

 experiments indicate greater stability under the first-named 

 condition. How to perform the first experiments with the 

 motor-driven machine is the difficulty which now awaits solu- 

 tion. If a large motor be used, the machine becomes too heavy 

 to be readily controllable ; if the dimensions of the machine 

 are kept down it becomes the more difficult to construct -a 

 sufficiently light and powerful motor. Theautomatic regulating 

 mechanism of Messrs. Chanute and Herring, by minimising the 

 effort required in ordinary balancing, may render it possible for 

 a man possessing the gymnastic skill of a Lilienthal or a Pilcher 

 to overcome by his agility the new difficulties, introduced, at 

 least in its early stages, by the motor. But in the transition 

 from the gliding machine to the flying machine proper a wide 

 gap has to be bridged, and it is little wonder that experimenters 

 hesitate before taking a step which may introduce unforeseen 

 dangers. It is by reducing the difficulty of balancing large 

 machines, on the one hand, and reducing the weight of motors 

 on the other, that we must hope to arrive at an experimental 

 demonstration of the possibility of artificial flight. 



