BALLOONS AS AIR-SHIPS. 



by their lightness and volume, as a balloon 

 does. A bird, with its pointed beak, wedge- 

 shaped head, gently swelling neck, chest, and 

 body, is admirably adapted for swiftly cleaving 

 the air, better than any machine can be which, 

 like a balloon, has to sustain itself by floating. 

 And, with its wings edge on, a bird presents 

 a remarkably small front to the air in the 

 direction of movement. 



How different it would be if birds sustained 

 themselves, not by beating the air with wings, 

 but by being light enough for their size that 

 is, large enough for their weight to float ! 

 A little bird weighing an ounce and a quarter 

 would then have to occupy a cubic foot of 

 volume, and allowing that it was cigar-shaped, 

 and that its length was ten times its diameter, 

 it would still present a front end of more than 

 twenty-eight square inches surface an enor- 

 mous object for a little bird of one and a quarter 

 ounces weight to drive swiftly through the air. 



Or take the case of a bird which can only 

 just contrive to fly at all a goose weighing 

 ten pounds. For such a goose to rise by mere 

 buoyancy it would have to occupy a space 

 of 130 cubic feet. With the cigar-shape again, 

 and the length ten times the diameter, the 

 front end area to be driven through the air 

 would be over six square feet. It is difficult 

 to imagine, and would be impossible to con- 

 struct, any motor, physiological, mechanical, 



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