CHANGING IDENTITIES 



tracted by the withdrawal of heat. (Common ex- 

 perience.) Therefore, there are in all substances 

 spaces not occupied by that substance. (Prop. V, 

 B. 1.) But somewhere the expansion by heat stops, 

 and the last identical atom is not decomposed by it. 

 There is then a difference in the construction of 

 an atom and the tangible, visible product of the 

 many-fold multiplication of the atom in a sub- 

 stance. (Def. 9.) Therefore, the ordinary expan- 

 sion of substances by heat is not an enlargement 

 of interstices in the molecules, but of the interstices 

 between the several molecules composing the sub- 

 stance heated. 



PROPOSITION XI. 



In the transmission of force from one body to 

 another body, every spheral body acts as if the 

 whole force proceeded from or was directed to the 

 centre. 



Substituting for force the word gravity, we have 

 one of Newton's laws, which he has fully demon- 

 strated. 



But gravity necessarily makes the background 

 for the action of any other manifestation of force. 



Therefore, the one universal force, acting 

 through a similar form, must act in a similar way, 

 if it is not altered through the intervention of 

 other forms. 



The action of spheral bodies, as observed in the 

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