The Three Secretaries 229 



that fly by flapping their wings, but of those that fly without 

 flapping their wings, and with almost no visible expenditure 

 of force.' 



" It was from watching the soaring birds that Professor 

 Langley came to conclude that it was possible to build solid 

 models very much heavier than the air and drive and direct 

 such a machine with such an ordinary force as steam. That 

 is to say, he became convinced that there are certain shapes 

 in which matter can be disposed so that the more rapidly it 

 moves through the air, in a sense, the less power it takes to 

 move it, and that a machine could be built to skim through 

 the air very much as a skater skims along the surface of very 

 thin ice — the faster you go the less danger. 



" Professor Langley believed that soaring birds have an in- 

 tuitive knowledge of certain properties in the air by which 

 they are able to skim along — rising and falling, soaring up 

 and sailing down, and turning about in circles without any 

 flapping of their wings or apparently any other effort. Just 

 what these properties were he attempted to find out and de- 

 velop by experiment. 



*' Well, the upshot of the matter was that from these experi- 

 ments it was demonstrated that a machine, not a balloon, can 

 be made which will produce enough mechanical power to 

 support itself in the air and fly. 'Though,' Professor Lang- 

 ley adds, ' this is not saying that we have got skill enough to 

 manage this power so as to rise and fly about in the air and 

 descend safely.' What is actually demonstrated, repeated 

 hundreds of times in the laboratory, and, finally, with the suc- 

 cessful machine which Professor Langley built, is that the fly- 

 ing machine is possible. All that now remains is to perfect 

 it and learn how to manaofe it. 



" The experiments which Professor Langley carried on re- 

 sulted in showing that an expenditure of one horse-power, in 

 horizontal flight, will support about 200 pounds, and at the 

 same time carry this burden at a rate of fifty miles an hour 

 through the air. Now, there have recently been built steam 

 engines which, with fuel and water for a short flight, weigh a 

 good deal less than twenty pounds. The relative weight of 



