266 THE STRUCTURE AND LIFE OF BIRDS chap. 



more dependable. These two investigators found 

 that in expenditure on flight muscle a big bird is 

 more economical than a small one of the same family, 

 a big Tern than a small Tern, a big. Gull than a small 

 Gull. Even when birds of different families are com- 

 pared, the rule generally holds. The Eagle and other 

 birds of strong flight have, for their size, lighter muscles 

 than small birds. The heavy-flying Geese are an ex- 

 ception. Incalculable factors complicate the problem, 

 but, clearly, many big birds can save in muscle and 

 devote more vital energy to other organs. 1 



Helmholtz undertook to show that a big flying bird 

 is an impossibility, since as the supporting power 

 increases the weight increases more rapidly. 2 This 

 runs quite counter to the figures just quoted. Even 

 if his calculation is right in the abstract, it ignores 

 some important facts that ought to make us hesitate 

 before we apply his conclusion to birds as they are. 

 It ignores the fact that the work done by a large wing 

 surpasses the work of a small wing by far more than 

 the superiority in area. It disregards what, if not 

 established fact, is yet not far from it, viz., that 

 pterodactyls, with wings measuring 25 feet from tip 

 to tip, were able to fly. It is now still further 



1 In three Terns, the comparative weights of which are repre- 

 sented by the figures 53, 116, 174, the total weights were 5jjj, 

 6 to> 7/oo times the weight of the breast-muscles in the re- 

 spective specimens. See Jahresbericht der Schlesischen Gesell- 

 schaft fiir Vaterland-Cultur. Breslau, 1879. 



2 The calculation was as follows : If the linear dimensions 

 increase as 1 : 4, then bulk and consequent weight (and presum- 

 ably strength) will increase as 1 : 4 3 , that is, as 1 : 64, but the 

 sustaining force must increase as 1 14^, that is, as 1 : 128. 



