32 GKAYITATION. 



whole power of this attraction was exerted be- 

 tween their respective centres of gravity ; and, 

 furthermore, you learned from me that if, in- 

 stead of a small ball I took a larger one, like 

 that [changing one of the balls for a much 

 larger one], there was much more of this at- 

 traction exerted ; or, if I made this ball larger 

 and larger, until, if it were possible, it became 

 as large as the Earth itself or, I might take the 

 Earth itself, as the large ball that then the 

 attraction would become so powerful as to cause 

 them to rush together in this manner [dropping 

 the ivory ball]. You sit there upright, and I 

 stand upright here, because we keep our centres 

 of gravity properly balanced with respect to the 

 earth ; and I need not tell you that on the 

 other side of this world the people are standing 

 and moving about with their feet towards our 

 feet, in a reversed position as compared with 

 us, and all by means of this power of gravita- 

 tion to the centre of the earth. 



I must not, however, leave the subject of 

 gravitation, without telling you something 

 about its laws and regularity; and first, as 

 regards its power with respect to the distance 

 that bodies are apart. If I take one of these 



