'THE LANGLEY AERODROME. 203 



p()ssil)h% and, having it, tiow b}' its means to acquire this horizontal 

 tiight in practice; that is, how to acquire the art of fiight or how to 

 build a ship that could actually navigate the air. 



One thing which was made clear by these preliminary expei-iuients, 

 and made clear nearly for the first time, was that if a surface be made 

 to advance rapidly, we secure an essential adv^antage in our ability to 

 support it. Clearly we want the advance to get from place to place; 

 but it proves also to be the only practicable way of supporting the thing 

 at all, to thus take advantage of the inertia of the air, and this point 

 is so all-important that we will renew an old illustration of it. The 

 idea in a vague sense is as ancient as classical times. Pope says: 



Swift Camilla scours the plain, 



Flies o'er the unbending corn, and skims along the main. 



Now, is this really so in the sense that a Camilla, by running fast 

 enough, could run over the tops of the corn? 7/^ she ran fast enough, 

 yes; but the idea may be shown better by the analogous case of a 

 skater who can glide safely over the thinnest ice if the speed is 

 sufficient. 



Think of a cake of ice of any small size, suppose a foot square. It 

 possesses (like everything else in nature) inertia or resistance to dis- 

 placement, and this will be less or more according to the mass moved. 

 If the skater stands during a single second upon this small mass it will 

 sink under him until he is perhaps waist deep in the water, while a 

 cake of the same width but twice the length will yield only about half 

 as readily to his weight. On this he will sink only to his knees, we 

 may suppose, while if we think of another cake ten times as long as 

 the first — that is, 1 foot wide and 10 feet long — we see that on this, 

 during the same second, he will not sink above his feet. This is all 

 plain enough; but now suppose the long cake to be divided into ten 

 distinct portions, then it ought to be equalh' clear that the skater who 

 glides over the whole in a second distributes his weight over just as 

 much ice as though all ten were in one solid piece. So it is with the 

 air. Even the viewless air possesses inertia; it can not be pushed 

 aside without some effort; and while the portion which is directly 

 under the airship would not keep it from falling several yards in the 

 first second, if the ship goes forward so that it runs or treads on 

 thousands of such portions in that time, it will sink in proportionately 

 less degree; smk perhaps only through a fraction of an inch. 



Speed, then, is indispensable here. A balloon, like a ship, will 

 float over one spot in safety, but our flying machine must be in motion 

 to sustain itself, and in motion, in fact, before it can even begin 

 to fly. 



Perhaps we may more fully understand what is meant by looking at 

 a boy's kite. Everyone knows that it is held by a string against the 



