APPENDIX. 2 I 7 



which can svnm high up out of water when 

 the air-cushions are full, and so feel very 

 " little the cold of the water beneath them, 

 breathe out all spare air, and sink almost 

 out of sight when they wish to be less con- 

 spicuous ; — just as a balloon sinks when part 

 of the gas is let out. And I have often 

 watched the common divers and cormorants 

 too, when frightened, swimming about with 

 only head and neck out of water, and so 

 looking more like snakes than birds. 



" Then about the Dippers : they ' fly ' to the 

 bottom of a stream, using their wings, just as 

 they would fly up into the air; and there is 

 the same difficulty in flying to the bottom of 

 the stream, and keeping there, as there would 

 be in flying up into the air, and keeping there, 

 — perhaps greater difficulty. 



" They can never walk comfortably along 

 the bottom of a river, as they could on the 

 bank, though I know they are often talked of 

 as doing it. They too, no doubt, empty their 

 air-bags, to make going under water a little 

 less difficult." 



155. This most valuable letter, for once, 

 leaves me a minute or two, disposed to ask a 



