ON TIIF. SUnMERGENCK OF WATER-DIRDS. 7 



power of floating on the surface of the water; or^ 



2nd. — It might so compress its body as to condense the air in the various 

 cavities to such an extent as to place it in the required condition. 



With regard to the first of these suppositions, namely, that the bird might 

 expel so much air as to remove its power of floating on the surface, although 

 it is considered by some writers on the subject to be a plausible explanation 

 of the phenomenon, I cannot think that it is the true one, for in the first 

 place, we have no evidence at all that the bird has any power, as to expulsion 

 at least, over the air in the various air cells, which constitute the great bulk 

 of the air vessels contained in the body of the bird; indeed the general 

 impression among anatomists is that it has no power at all over it; and even 

 if it had, I cannot think it would bo possible for the bird to expel it so 

 quickly as would be necessary to produce such an immediate effect, as does 

 actually take place; nor would the bird have the power of again taking it in 

 so rapidly as it manifestly must do, to enable it to float at its ordinary level 

 in so short a time after partial submergence as it in reality does. 



In a paper on this subject, the Bev. J. 0. Atkinson says, "Well, I will 

 shoot a Moorhen in the act of diving, and will add to its specific gravity 

 by depositing within its body some twenty or thirty grains of No. 5 shot. Of 

 course then it will sink; and unless my retriever is a rather uncommon one 

 I lose the bird. But no such thing; the Moorhen comes to the surface 

 immediately, and floats almost as buoyantly as ever; and yet whence and how 

 can the air have been procured, which has been, applied to the replenishing 

 of the air vessels, and the restoration of the bird's buoyancy." I will endeavour 

 when considering the second supposition to give what I believe to be the true 

 explanation of this fact, for it is only as a fact that it is brought forward by 

 Mr. Atkinson, as being opposed to the idea that the bird expelled the air from 

 its body before submergence, and which was the hypothesis of his opponent 

 Mr. Slaney. 



I have very little doubt in my own mind that the muscular system of the 

 bird would enable it so to compress its body, as to expel sufficient air to 

 make it of the same specific gravity as water, were the various air cavities so 

 arranged as to allow of free cgi'ess and ingress; but unfortunately for this 

 theory this is not the case, and I much doubt whether the removal of all air 

 in the numerous air cells, the bones, and feathers, would be possible even under 

 an air pump. Another argument also which bears strongly against this idea 

 is, that were the bird to get rid of the air from the air cavities, it could only 

 do so through the lungs, which thus must be in the same condition, and the 

 bird would necessarily become suffocated, for want of the absolutely essential 

 quantity of air for respiration, and which the bird can do without worse than 

 any other animal, for its circulation, and consequently its respiration, is very 

 rapid, and it is this which enables it to keep up its natural heat under cir- 

 cumstances that would be fatal to animals otherwise constituted. No; every 

 bird on diving has the power, if it sees reason to exercise it, of arresting its 



