NATATORES. 423 



or diminution by means of a beautiful muscular apparatus. 

 . . . . By this power the birds can raise or depress 

 themselves at will.' Now, I do not for a moment doubt the 

 existence of this apparatus, for it is well known that all birds 

 have it to a greater or less extent ; but I do doubt its capa- 

 bility of doing the duty assigned to it, viz. raising the bird 

 in the air. The temperature of the Albatros, as taken by Sir 

 G. Grey, by placing a thermometer under the tongue, is 98° F., 

 and if we add 10° E. to this, in order to allow for the differ- 

 ence between the head and the body, we shall have the tem- 

 perature of the air-cells at 108° F. The temperature of the 

 surrounding air cannot be taken lower than 48° F., as the 

 mean winter temperature of lat, 50° S. is about 50° F. The 

 bird, therefore, could not raise the temperature of the air taken 

 into these cells more than 60° F. This would increase its 

 volume not quite one-eighth ; and taking 100 cubic inches of 

 air to weigh 31 grains, and the average weight of an Albatros 

 to be 17 lbs., as given by Gould, it would be necessary, in 

 order that the specific gravity of the bird might be brought 

 to that of the atmosphere, that these cells should contain 1820 

 cubic feet of air ; or, in other words, they must be more than 

 1200 times the size of the body itself of the bird, which, to 

 say the least, would give it when flying an aldermanic appear- 

 ance which I have never observed. In fact it would require 

 a sphere of more than fifteen feet in diameter to contain the 

 necessary quantity of air. Even if it could thus buoy itself 

 up, it would entirely defeat its own object ; for it would at 

 once destroy the whole of its momentum, and unless propelled 

 forward by its wings, would drift helplessly to leeward. 

 However, I do not wish it to be inferred that I consider the 

 air-cells of no use. The greater portion of them are situated 

 round the neck, wings, and fore-part of the body of the bird, 

 and I believe that by their means he is enabled to shift 

 slightly the position of his centre of gravity, and thus, with 

 very slight muscular exertion, to vary the inclination of his 



