112 MECHANISM OF THE BONES. 



be inconvenient in the air, by occasioning a greater 

 resistance from the air, while he is moving along, no 

 sooner does he lift the hoof, than the two parts into 

 which it is cloven fall together, and so lessen the sur- 

 face exposed to the air." 



T. But there is another structure of the foot 

 which will lead us still farther to admire the wisdom 

 and contrivance exhibited in the animal mechanism. 



A. It is that of the fly, by which it is enabled to 

 walk upon a perpendicular wall. 



B. This motion in these little insects always 

 seems unaccountable, especially when they run so 

 fast upon a glass window. The only reason I can 

 think of is, that they have something sticky upon 

 their feet, — or that there are rough places in the 

 glass or wall by which they are able to climb up. 



T. Any thing adhesive upon the foot would be 

 a constant impediment, especially to an insect, — and 

 to have to climb up upon points would be excessively 

 inconvenient. They are enabled to perform this mo- 

 tion by a most curious philosophical contrivance. 

 Can you describe it? It forms one of the innumerable 

 instances in which we discover the powers of science, 

 if we may so express it, subservient to the opera- 

 tions of an all wise and Creative Intelligence. 



A. The air is said to exert a pressure upon bodies 

 equal to between fourteen or fifteen pounds to every 

 square inch of surface, so that upon one of our hand, 

 the weight of the atmosphere is more than two hun- 

 dred and fifty pounds. The hand is not borne down- 

 ward* because the air presses alike in every direction } 



