36 INTRODUCTION. 



The number of springs and paddings upon the feet 

 of animals, by which their fall is broken, and their 

 bodies prevented from being injured, when they alight 

 on the ground, after rapid motion, with the hooks, and 

 pumps, and suckers, by means of which they are en- 

 abled at once to fasten themselves to the smoothest sur- 

 faces, though perpendicular, or even the under sides of 

 horizontal ones, are truly wonderful ; and no one can 

 examine the structure, or even watch the motions, of a 

 common house-fly, without perceiving that in science 

 of design, and elegance of execution, it is superior to 

 all the engines that ever man invented. The moment 

 that its little feet touch the surface, they adhere, by 

 the action of two small webs or membranes, one on 

 each side of the foot, which touch the surface, first in 

 the middle, and then gradually to the outsides, so as to 

 exclude the air ; and as the weight of the fly is con- 

 nected to the middle of each sucker, they never miss 

 their hold, until it relieves them first at the outsides. 

 Thus we have a series of motions all perfectly explain- 

 able upon the established doctrines of matter, as indeed 

 all mechanical contrivances for the motion of matter 

 must be, whether the "work of nature or of art. But 

 all this, which in the hands of the most expert me- 

 chanic, would require a considerable time, is done by 

 the fly in an instant. In all animals that bound and 

 leap by rapid motion, the padding of the feet, which is 

 formed of a substance not very unlike Indian rubber, 

 is of the utmost importance. The foot of the horse 

 may be taken as an example. When the horse bounds 

 forward, the point from which he takes his spring is 

 the fore-part of the hoof, because that takes a firm 



