ASTRONOMICAL INSTRUMENTS. 

 Fig. 122. 



Ill 



or moons, which are in these instruments only movable by 

 the hand. 



We turn the handle, and all the planets are put in motion, 

 moving round that ball which represents the sun. Now, if 

 you take the earth's motion as a standard, they move with 

 nearly the same relative velocities and periodical times that 

 they observe in the heavens. We scarcely need observe, 

 that it is impossible to give an idea of the proportion and 

 distances of the planets in the compass of an instrument so 

 small as that before you, or indeed of any instrument what- 

 soever. 



