2 POPULAR LECTURES AND ADDRESSES. 



action. But neither he nor any one else had 

 suggested that heaviness is the resultant of mutual 

 attractions between all parts of the heavy body 

 and all parts of the earth, and it had not entered 

 the imagination of man to conceive that different 

 portions of matter at the earth's surface, or even 

 the more dignified masses called the heavenly 

 bodies, mutually attract one another. Newton 

 did not himself give any observational or experi- 

 mental proof of the mutual attraction between 

 any two bodies, of which both are smaller than the 

 moon. The smallest case of gravitational action 

 which was included in the observational founda- 

 tion of his theory, was that of the moon on the 

 waters of the ocean, by which the tides are 

 produced ; but his inductive conclusion that the 

 heaviness of a piece of matter at the earth's 

 surface, is the resultant of attractions from all 

 parts of the earth acting in inverse proportion 

 to squares of distances, made it highly probable 

 that pieces of matter within a few feet or a few 

 inches apart attract one another according to the 

 same law of distance, and Cavendish's splendid 

 experiment verified this conclusion. But now 



