MECHANICAL PARADOXES. 



electrical, or thermodynamic, powerful enough 

 to drive such a surface at the rate of fifty, 

 sixty, or seventy miles an hour, and yet light 

 enough to come within that part of the goose's 

 ten pounds of weight which is not taken up 

 by the framing and structure of the bird in 

 its hypothetically swollen form. 



For it must be remembered that the air 

 pressure increases more than proportionally 

 with the area exposed. 



The air-pressure itself on large surfaces 

 becomes so enormous as to be destructive for 

 a thing which, like a balloon, has to be built 

 with a construction light enough to let it float 

 in air. Imagine our goose with a great part 

 of its ten pounds of weight taken up by muscle 

 tendons and bones powerful enough to force 

 so large a body through the air at sixty miles 

 an hour, and having only the remainder of 

 its ten pounds available to make the frame 

 and covering of a bulk of 130 cubic feet strong 

 enough to stand the tremendous pressure of 

 being driven at express railway speed ! To 

 state the problem is to see how insoluble it is. 



The paradox of the balloon air-ship, then, 

 may be stated briefly as follows : 



To be independent, or even safe, in a fluid 

 as swift as the winds, it must itself be as swift 

 as an express train. 



To resist the air-pressure at so high a speed 

 it must be very strong, and therefore heavy. 



68 



