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mals : the immense power thus acquired being 

 no more than is necessary to enable them at once 

 to support themselves in the air, and to move 

 through it with such astonishing velocity. The 

 former they effect by continually renewing the 

 column of air below them and which must be 

 displaced, in order to allow of their falling to the 

 ground more rapidly than this displacement 

 can take place, and the latter by using their 

 wings in the manner of oars, while the tail, at 

 the same time, serves them for a rudder ; and 

 so powerful is the impulse acquired in this way, 

 that they not unfrequently travel at the rate of 

 sixty or one hundred miles in an hour, or over 

 a distance equal to that between the capitals of 

 Scotland and England, in the same time that an 

 ordinary stage-coach takes to travel about thirty 

 miles. The advantage to birds, as well as to in- 

 sects, of the great quantity of air which prevades 

 their bodies even their bones has been already 

 pointed out ; and this obvious subserviency of 

 one part of their structure to the rest, irresist- 

 ably inculcates the truth that one Master-hand 

 has regulated the whole. 



The loco-motion of mammiferous animals need 

 not detain us long. The cetaceous tribes alone 

 move constantly in the water ; and this they ef- 

 fect almost in the same manner as fishes, taking 

 care, however, to keep the summit of the head 

 which is often loaded with a kind of fat for this 

 purpose always above the surface, in order not 

 to interfere with respiration. It is from the 



