II THE SWALLOW. 5 J 



as if the main difficulty of it were onl}^ in 

 keeping up in the air; — but the buoj^ancy is 

 coi?reivab!c enough, the far more wonderful 

 matter is the getting along. You find it hard 

 work to row yourself 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 impulses, it secedes as easily from the 

 blow that gives it. And if 3^ou think what an 

 effort 3-ou 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 3'ou, I think, 

 greatly marvellous. Yet of the mode in which 

 it is accomplished 3'ou will as yet find no 

 undisputed account in any book on natural 

 history, and scarcely, as far as I know, 

 definite notice even of the rate of flight. 

 What do you suppose it is ? We are apt 

 to think of the migration of a swallow, as we 

 should ourselves of a serious journey. How 

 long, do you think, it would take him, if he flew 

 uninterruptedl3', to get from here to Africa ? 



