954 



SCIENCE. 



[N. S. Vol. XIX. No. 495. 



walli on four legs, imitating a horse, was not 

 a success, while the round leg as a wheel, act- 

 ing continuously, was all that was wanted, so 

 too the lifting and propelling fans, being in- 

 tended for .continuous motion, should do the 

 work of wings and, better than reciprocating 

 mechanical appliances, made to flap, condense 

 the air, lift the body, release and flap again. 



General Butler was so impressed when he 

 saw the drawing and heard the explanation, 

 that he ordered the machine to be built at 

 once, and put the work in my charge. 



There was, however, no appropriation that 

 could be used to pay for it, and it seemed that 

 nothing could be done; there was a very good 

 engineer park, but the tools and machines at 

 disposal were not fine enough to cut gear or 

 to bore cylinders. Fortunately some patriotic 

 citizens, who should be forever remembered, 

 generously offered to pay the bills. Mr. Fred- 

 erick Prentice, Mr. "Wedworth W. Clarke, of 

 New York City, and Mr. Sully, who were 

 among the pioneers in the petroleum fields 

 and were growing rich very fast, said : ' Send 

 the bills to us; we will pay for anything 

 wanted and will help to get it.' 



The first thing done was to make a fan 

 eighteen inches in diameter, rotate it at dif- 

 ferent speeds and see how much it would lift. 

 The fan was made of very thin brass, and 

 upon a wire frame, very much the same shape 

 as those now used for ventilating and blow- 

 ing, driven by electricity. It was found that 

 a hollow blade with a blunt shoulder seemed 

 to be best. 



It was found that very considerable weight 

 could be lifted, and to try what could be done 

 on a large scale, a fan about thirty-two feet 

 in diameter was made, the blades of the thin- 

 nest sheet iron that could be procured, and 

 rotation by belt was provided. 



Contrary to expectation, when the fan was 

 first rotated at great speed in a foundry that 

 had a high roof, the weight that could be lifted 

 was much more than the wheel itself, some 

 six hundred pounds or more, and then within 

 forty seconds of time the wheel and the 

 weights would drop back to where they started 

 from, it mattered not how fast the fan was 

 driven. 



This was a puzzle, indeed. Why did it act 

 so? When spun at a given speed, starting 

 from at rest in still air, a certain velocity 

 would make the wheel jump up the vertical 

 shaft very quickly, lifting its own weight, and 

 then suddenly, and as the velocity was in- 

 creased, it would, after an interval never 

 longer than forty seconds, slide down the ver- 

 tical shaft, not sustaining its own weight. 

 Hundreds saw it. The test was repeated 

 again and again. No one understood why it 

 did as it did. 



Eesort was then had again to the eighteen- 

 inch brass wheel and it was found that after 

 a certain period it went through the same 

 manoeuvers as the large fan, but the period of 

 ability to lift was many times longer in the 

 small than in the large. 



It was found after a long investigation that 

 the fan wheel of any size, when rotated in one 

 place, set up a dovmward current of air that 

 soon became nearly or quite as fast as the 

 pitch of the fan, hence it would lift nothing. 

 When, however, the fan was mounted at the 

 outer end of a long boom, which revolved 

 around a mast, so as to constantly bring the 

 fan into new air, its lifting capacity never 

 deserted it and bore a certain ratio to the 

 velocity, and data were accumulated for pro- 

 portioning the machine. 



In those days there were no such machines 

 as are now to be found everywhere, by which 

 the horse power required at different veloci- 

 ties could readily be accurately measured, and 

 some difficulty was experienced in approxima- 

 ting the requirements. 



The questions involved seemed to be the size 

 of the fan, the shape of the blade, the power 

 required, the weight of the engine, boiler, fuel 

 and water to develop the power. 



Major-General Quincy A. Gillmore was an 

 engineer officer of very high reputation and of 

 considerable learning. He was asked to ex- 

 amine the plans and the data that had at this 

 stage of the investigation been collected. He 

 certified as a matter of opinion that it was 

 ' all right.' 



There were no dynamos or storage batteries, 

 liquid air engines or sources of powerful en- 

 ergy using light-weight machines, and the only 



