COHESION OF SOLIDS. 159 



of Newton's authority on nearly all subjects 

 connected with the science of nature, it is im- 

 portant that his real opinions should be distinctly 

 understood. I shall, therefore, proceed to prove, 

 by his own words, that he did not regard attrac- 

 tion as an ultimate law of nature, resulting from 

 the inherent properties of atoms. In addition to 

 the passages before quoted, in page 26 of this 

 work, he observes, in the advertisement to the 

 second edition of the Opticks, " to show that I do 

 not take gravity for an essential property of 

 bodies, I have added one question concerning its 

 cause, choosing to propose it by way of question, 

 because I am not satisfied about it for want of 

 experiments."* 



The same view is still further expanded in the 

 third book of the Opticks, page 365. After ob- 

 serving that " all matter, even light, seems to be 

 composed of exceedingly small, hard, and un- 

 changeable atoms, which in the densest bodies 

 touch only in a few points," he adds, " how they 

 can stick together so firmly as they do without 

 the assistance of something which causes them 

 to be attracted or pressed towards one another, 

 is very difficult to conceive." He remarks, in 

 another passage, page 369, " there are agents in 

 nature capable of causing the particles of matter 

 to stick together by very strong attractions, and 



* The above sentence refers to the cether, which, in the second 

 edition of the Principia, he proposed hypothetically as the cause 

 of universal attraction. 



