Birds. 1255 



land ; it is said to be common and resident on some of the lakes of 

 the latter. 



Little Grebe or Dabchick, Podiceps minor. This species might 

 have been placed in my group a, as a certain number nestle with us, 

 but the majority being migratory, I have preferred mentioning it here. 

 The history of this species is better known than that of any other 

 grebe, and most interesting accounts of its habits have appeared in 

 6 The Zoologist ' from the pens of Messrs. Atkinson and Parsons. 



I do not believe that this bird has the power of stationary submer- 

 sion, its flat and subcoriaceous feet being very ill-formed for taking 

 hold of plants or other substances, which I consider the means employed 

 by the moorhen {Gallinula chloropus). I do not think (and Mr. At- 

 kinson seems to be of the same opinion) that birds possess the volun- 

 tary power of suddenly expelling air from their air-cells, or of pre- 

 venting it from introducing itself into them; this, however, even if it 

 took place, would not much diminish the bird's bulk, as the cells 

 have, I believe, no movements of contraction of their own, and the 

 lungs could certainly not be deprived of air without causing almost 

 instantaneous death by suffocation. 



Although I do not like being at variance with any intelligent na- 

 turalist, I am sorry not to be able to side with Mr. Slaney's state- 

 ments (Zool. 667) ; and as the great aim of the studies of naturalists is 

 the attainment of true principles and undeniable facts, I hope he will 

 excuse the following lines, and that they will induce him to change 

 his, perhaps, too hastily formed opinions respecting the submersion of 

 water-birds. 



It is well known to all who have opened a book on physics, that 

 any substance floating on a liquid loses a quantity of its weight equal 

 to the weight of the volume of liquid displaced. Now, a moorhen, or 

 any other bird while swimming, displaces a volume of water which is 

 equal, or more than equal, in weight to the weight of its body ; that 

 is to say, in other words, that its specific gravity is less than that of 

 water. 



If, then, muscular contraction took place, sufficient to make the 

 difference in bulk (which causes the displacement of the volume of 

 water) equal to a sum which would be less than the weight of the 

 bird, it would sink of itself ; but if no such contraction took place, the 

 simple exclusion of air from the cells would not be sufficient in itself 

 to occasion submersion. For instance, let us suppose a moorhen 

 weighs 2 pounds, to remain above water it must displace a volume 

 of water weighing as much or more than 2 pounds, let us say 2j ; for 



