MASS OF THE EARTH. 49 



pressure of the atmosphere; for differences in this 

 pressure appear to exercise a powerful influence 

 on the functions of plants, and to require differ- 

 ences of structure. But we pass over these con- 

 siderations. The slightest attention to the rela- 

 tions of natural objects will show that the subject 

 is inexhaustible ; and all that we can or need do 

 is to give a few examples, such as may show the 

 nature of the impression which the examination 

 of the universe produces. 



3. Another instance of the adjustment of or- 

 ganic structure to the force of gravity may be 

 pointed out in the muscular powers of animals. 

 If the force of gravity were increased in any con- 

 siderable proportion at the surface of the earth, it 

 is manifest that all the swiftness, and strength, and 

 grace of animal motions must disappear. If, for 

 instance, the earth were as large as Jupiter, gra- 

 vity would be eleven times what it is ; the light- 

 ness of the fawn, the speed of the hare, the spring 

 of the tiger, could no longer exist with the ex- 

 isting muscular powers of those animals ; for man 

 to lift himself upright, or to crawl from place to 

 place, would be a labour slower and more pain- 

 ful than the motions of the sloth. The density 

 and pressure of the air too would be increased to 

 an intolerable extent, and the operation of respi- 

 ration, and others, which depend upon these me- 

 chanical properties, would be rendered laborious, 

 ineffectual, and probably impossible. 



