396 THE POPULAR SCIENCE MONTHLY. 



metres in a second. The simple theoretical calculation deduced 

 from the experimental fact assigns 3"375 kilogrammes to the mo- 

 tor that will develop seventy-five kilogrammes. But so minute a 

 motor returns only about twenty per cent of the energy which is 

 confided to it, while a motor of from fifty to one hundred horse- 

 power will return eighty, ninety, or one hundred per cent. It is 

 possible, therefore, and seems to be reasonable, that a large electric 

 motor, the power of which increases faster than the weight, would 

 employ the surplus of sixty or seventy per cent in raising the gen- 

 erator, the propeller, and the aeronaut. We do not intend to hy- 

 pothecate the future and form tables on gratuitous suppositions, 

 probable as they may seem. We therefore, for the moment, lay 

 aside the electric motor, because, with its generator and propeller, 

 it exceeds the weight of 3'5 kilogrammes per horse-power, which 

 we have imposed upon ourselves as the minimum. 



We now come to accumulators of energy. India rubber, for 

 example, the elasticity of which is often utilized as a reservoir of 

 power, and has a potential, in this point of view, fifteen times 

 superior to that of steel, furnishes power and motion together. 

 Joining to it an immediate organ of resistance to the air, we have 

 an apparatus heavier than air. Penaud chose admirably ; and 

 one of the first helicopters was formed upon this plan. But, while 

 India rubber stores a large sum of energy, it expends it faster than 

 it obtains it, and can not of itself renew the provision. Penaud 

 had only a small success with it, because the thongs he used were 

 placed and displaced too slowly ; and if he had found a means of 

 changing them more rapidly, the considerable charge of his pro- 

 vision would have made him lose the primary advantages of his 

 judicious choice. 



Compressed air motors and gas motors enjoy a certain repute 

 which is in many respects deserved ; but as they are constructed, 

 they require the assistance of lubricating and refrigerating appa- 

 ratus which have weight, and are thus excluded for the preseiit 

 from the list of applications for aerial locomotion. So there are 

 no steam motors, or electric motors, or accumulators of energy like 

 India rubber, or steel, or compressed air motors or generators, that 

 fully answer the requirements. None of them, as they are, supply 

 such coexisting conditions of power and levity as are strictly im- 

 posed by the nature of the problem. Is it, then, true that there is 

 now no motor with its accessories, the generator and propeller, 

 which can be used at once, or at least improved upon, for the pur- 

 pose we have in view ? The comparative experiments which 

 we have reported, and have verified with our new universal 

 direct-reading dynamometer, which we had the honor of pre- 

 senting to the Academy on the 23d of June, 1891, seem to attest 

 this. Still, if the generator and propeller, mutually necessary. 



