42 



distinct relation between tlie shapes of birds and their 

 powers of flight. I suppose the form of the body is first 

 determined by the general habits and food, and that 

 nature can make any form she chooses volatile ; only one 

 point I think is always notable, that a complete master of 

 the art of flight must be short-necked, so that he turns 

 altogether, if he turns at all. You don't expect a swallow 

 to look round a corner before he goes round it ; he must 

 take his chance. The main point is, that he may be able 

 to stop himself, and turn, in a moment. 



47. The stoj^ping, on any terms, is diflicult enough to 

 understand ; nor less so, the original gaining of the pace. 

 "We always think of flight as if the maiji difliculty of it 

 were only in keeping up in the air ; — but the buoyancy is 

 conceivable enous'h, the far more wonderful matter is the 

 getting along. You find it hard work to row youi-self at 

 anything like speed, though your impulse-stroke is given 

 in a heavy element, and your return-stroke in a light one. 

 But both in birds and fishes, the impelling stroke and its 

 return are in the same element ; and if, for the bird, that 

 medium yields easily to its impulse, it secedes as easily 

 from the blow that gives it. And if you thiuk what an 

 effort you make to leap six feet, with the earth for a 

 fulcrum, the dart either of a trout or a swallow, with no 

 fulcrum but the water and air they penetrate, will seem to 

 you, I think, greatly marvellous. Yet of the mode in 

 which it is accomplished you will as yet find no un- 

 disputed account in any book on natural history, and 



