38 Astronomy and Geology compared. PT. i. 



races of animals existed at remote periods upon 

 the Earth, and have become extinct from different 

 causes : it is quite possible to conceive that analo- 

 gous causes might extirpate man; but all these 

 changes need not affect the course of the planets, 

 or the position of the Earth as a member of the 

 Solar System. Uninfluenced by these changes, the 

 great mass of our Globe might continue to fill its 

 accustomed place in the system of which it is a 

 member. 



The whole of the beautiful scheme of our Solar 

 System, so complicated and yet so perfect in its 

 working, gives the most convincing proof of design. 

 Its vast mechanism is to be traced to the combined 

 agency of two forces in nature directly opposed to 

 each other, and therefore modifying the effects pro- 

 duced by each. The first of these is the universal 

 law of gravity, by which all bodies are attracted to 

 each other ; the vast mass of the Sun would *under 

 this influence absorb the whole planetary -system 

 within itself, were not its action controlled by the 

 centrifugal force imparted to all these bodies, and 

 which gives them a tendency to fly off in a straight 

 line, as a sj:one does when escaping from a sling. 

 What that force is may be conceived, when we 



