204 THE LANGLEY AEEODKOME. 



wind, which sustains it, and that it falls in a cahn. Most of us remem- 

 ber that even in a cahii, if we run and draw it along it will still keep 

 up, for what is required is motion relative to the air, however 

 obtained. 



It can be obtained without the cord if the same pull is given by an 

 engine and propellers strong enough to draw it and light enough to be 

 attached to and sustained by it. The stronger the pull and the quicker 

 the motion, the heavier the kite may be made. It may be, instead of 

 a sheet of paper, a sheet of metal even, like the plate of brass which 

 has already been mentioned as seeming, when in rapid motion, to float 

 upon the air, and, if it will make the principle involved more clear, 

 the reader may think of our aerodrome as a great steel kite made to 

 run fast enough over the air to sustain itself, whether in a calm or in 

 a wind, by means of its propelling machinery, which takes the place 

 of the string. 



And now, having the theory of the flight before us, let us come to 

 the practice. The first thing will be to provide an engine of unprece- 

 dented lightness that is to furnish the power. A few years ago an 

 engine that developed a horsepower weighed nearly as much as the 

 actual horse did. We have got to begin b}" trying to make an engine 

 which shall weigh, everything complete, boiler and all, not more than 

 20 pounds to the horsepower, and preferably less than 10; but even 

 if we have done this very hard thing we may be said to have only 

 fought our way up to an enormous difficulty, for the next question 

 will be how to use the power it gives so as to get a horizontal flight. 

 We must then consider through what means the power is to be applied 

 when we get it, and whether we shall, for instance, have wings or 

 screws. At first it seems as though nature must know best, and that 

 since her flying models, birds, are exclusively employing wings, this 

 is the thing for us; but perhaps this is not the case. If we had imi- 

 tated the horse or the ox, and made the machine which draws our 

 trains walk on legs we should undoubtedly never have done as well as 

 with the locomotive rolling on wheels; or if we had imitated the whale, 

 with its fins, we should not have had so good a boat as we now have in 

 the steamship with the paddle wheels or the screw, both of which are 

 constructions that nature never employs. This is so important a point 

 that we will look at the way nature got her models. Here is a human 

 skeleton, and here one of a bird, drawn to the same scale (PI. I). 

 Apparently nature made one out of the other, or both out of some 

 common type, and the closer we look the more curious the likeness 

 appears. 



Here is a wing from a soaring bird, here the same wing stripped 

 of its feathers, and here the bones of a human arm, on the same scale. 

 IMow, on comparing them, we see still more clearly than in the skeleton 

 that the bird's wing has developed out of something like our own arm. 



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