262 



PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



stroke of the "wiug, increasing in proportion to the size of the bird, mul- 

 tii)lies the resistance which the wing meets from the air, and the reac- 

 tion bears a simihir proportion to the weight of tlie birds themselves. 

 Dr. Hurean de Villeneuve, upon the same principle, has sought to de- 

 termine the alar extent which would enable a bat of the same weiglit 

 as a man to fly. He found that each*of its wings would be less than 

 three meters in length. 



A renmrkable work by Hastings* has appeared this year on the rela- 

 tive extent of the wings and the weight of the pectoral muscles in the 

 different species of flying vertebrate animals. The author first shows 

 that among birds the existence can be established of a certain relation 

 between the surface of the wings and the weight of the body. But we 

 should be careful to compare only comparable elements ; that is to say, 

 the length of the wings, the square roots of the alar surfaces, and the 

 cube roots of the weight among different birds. Let I be the length of 

 the wiug, a its area, and w the weight of the body, we can compare 

 among themselves /, Vrt^ ^/w. 



Examining different types of bird, Hastings made weights and mea- 

 surements, from which the following table is extracted : 



Species. 



Larus arj^entatus . . 



Anas uyroca 



Fulica atra 



Nettion crecca 



Laus ridibuudus . . . 

 Machetes puj;;iiax . . 

 Rallus aquaticiis . . 



Tardus pilaris, 



Tiirdus nieriila 



Stnrniis vulgaris . . 

 Ijombycilla garrula 



Alauda arveusis 



Parus major 



Friugilla spiuns . . . 

 Parus ciieruleus 



The weight of the pectoral muscles is, on the contrary, in simple pro- 

 portion to the total weight of the bird, and in spite of the difterences 

 which correspond to the diflerent degrees of a|)titude to flight with 

 which each species is endowed, we perceive that the proportion of the 

 weight of the pectoral to the total weight is about one-sixth in the 

 greater nnmber of birds. 



Each animal capable of sustaining itself in the air must develop a 

 force proportional to its own weight, and should possess an amount of 

 muscle proportioned to this weight; for, as we have seen, if the chemi- 

 cal action which takes place in the wings of birds be always of the 

 same nature, this chemical action and the power which it generates will 

 be proportionate to the size of the muscular masses. Now, how is it 

 that the wings of birds in which the surface varies as the square of the 

 linear dimensions suffice to move bodies of which the variation is in 

 proportion to the cubes of these dimensions ? Here it is necessary to 



* Archives Necrlandaises, t. iv. 1869. 



