154 THE REIGN OF LAW. 



the air at the rate of more than a hundred miles 

 an hour. Such especially are the powers of some 

 species of the Swallow tribe, one of which, the 

 common Swift, is a creature whose wonderful and 

 unceasing evolutions seem part of the happiness 

 of summer and of serene and lofty skies.* 



There are other birds in which the wing has to 

 be adapted to the double purpose of swimming, 

 or rather of diving, and of flight. In this case, a 

 large area of wing must be dispensed with, be- 

 cause it would be incapable of being worked under 

 water. Consequently in all diving birds the wings 

 are reduced to the smallest possible size which is 

 consistent with retaining the power of flight at all ; 

 and in a few extreme Forms, the power of flight is 

 sacrificed altogether, and the wing is reduced to 

 the size, and adapted to the function, of a powerful 

 fin. This is the condition of the Penguins. But 

 in most genera of swimming Birds, both purposes 

 are combined, and the wing is just so far reduced 

 in size and stiffened in texture as to make it work- 

 able as a fin under water, whilst it is still just large 



* For the form of the wing in this remarkable bird, see the beauti- 

 ful drawing here engraved from the pencil of Mr Wolf. 



