FLYING AND FLYING-MACHINES. 335 



of Australia, and possesses relatively 140 times more 

 surface than this latter, which is the heaviest bird 

 M. de Lucy had weighed, and was that also which had 

 the smallest amount of surface, the weight being 

 nearly 21 Ibs.; and the supporting surface 139 inches 

 per kilogramme (2 Ibs. 3 oz.). Yet of all travelling 

 birds the Australian cranes undertake the longest and 

 most remote journeys, and, with the exception of 

 the eagles, elevate themselves the highest, and maintain 

 flight the longest.' 



M. de Lucy does not seem to have noticed the law 

 to which these numbers point. It is exceedingly simple, 

 and amounts in fact merely to this, that instead of the 

 wing-surface of a flying creature being proportioned to 

 the weight, it should be proportioned to the surface of 

 the body (or technically, that instead of being propor- 

 tioned to the cube, it should be proportioned to the 

 square of the linear dimensions). Thus, suppose that 

 of two flying creatures one is 7 times as tall as the 

 other, the proportions of their bodies being similar, 

 then the body surface of the larger will be 49 times 

 (or 7 times 7) that of the other, and the weight 343 

 times (or 7 times 7 times 7) that of the other. But 

 instead of the extent of wing-surface being 343 times 

 as great, it is but 49 times as great. In other words, 

 relatively to its weight the smaller will have a wing- 

 surface 7 times greater than that of the larger. How 

 closely this agrees with what is observed in nature, will 

 be seen, by the case of the sparrow as compared with 

 the Australian crane; for M. de Lucy's experiments 



