LECTURE II 



GRAVITATION COHESION 



DO me the favor to pay me as much attention as you 

 did at our last meeting, and I shall not repent of 

 that which I have proposed to undertake. It will be 

 impossible for us to consider the Laws of Nature, and what 

 they effect, unless we now and then give our sole attention, 

 so as to obtain a clear idea upon the subject. Give me now 

 that attention, and then I trust we shall not part without 

 our knowing something about those laws, and the manner in 

 which they act. You recollect, upon the last occasion, I 

 explained that all bodies attracted each other, and that this 

 power we called gravitation. I told you that when we 

 brought these two bodies [two equal-sized ivory balls sus- 

 pended by threads] near together, they attracted each other, 

 and that we might suppose that the whole power of this 

 attraction was exerted between their respective centres of 

 gravity; and, furthermore, you learned from me that if, 

 instead of a small ball I took a larger one, like that [chang- 

 ing one of the balls for a much larger one], there was much 

 more of this attraction 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 bal- 

 anced 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 toward our feet, in a reversed 

 position as compared with us, and all by means of this power 

 of gravitation to the centre of the earth. 

 I must not, however, leave the subject of gravitation with- 



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