222 KINETIC THEORIES OF GRAVITATION. 



endowed with a secret or occult quality, by which they are mutually 

 attracted. On this question philosophers are divided. Some are of 

 opinion that this phenomenon is analogous to an impulsion 5 others 

 maintain with Newton, and the English in general, that it consists in 

 attraction."* 



"To avoid all confusion which might result from this mode of ex- 

 pression, it ought rather to be said that bodies move as if the.v mutually 

 attracted each other. This would not decide whether the powers which 

 act on bodies reside in the bodies themselves or out of them ; and this 

 manner of speaking might thus suit both parties. Let us confine our- 

 selves to the bodies which we meet with on the surface of the earth. 

 Every one readily admits that all these would fall downward, unless 

 they were supported. Now the question turns on the real cause of this 

 fall. Some say that it is the earth which attracts these bodies, by an 

 inherent power natural to it ; others that it is the a3ther, or some other 

 subtile or invisible matter, which impels the body downward, so that the 

 effect is nevertheless the same in both cases. 



" This last opinion is most satisfactory to those who are fond of clear 

 principles in philosophy, as they do not see how two bodies at a distance 



can act upon each other if there be nothing between them 



Let us suppose that before the creation of the world, God had created 

 ouly two bodies, at a distance from each other ; that absolutely nothing 

 existed outside of them, and that they were in a state of rest; would it 

 be possible for the one to approach the other, or for them to have a pro- 

 pensity to approach? How could the one feel the other at a distance ? 

 Whence could arise the desire of approaching ? These are perplexing 

 questions. But if you suppose that the intermediate space is filled with 

 a subtile matter, we can comprehend at once that this matter may act 

 upon the bodies by impelling them. The effect would be the same as 

 if they possessed a power of mutual attraction. Now as we know that 

 the whole space which separates the heavenly bodies is filled with a sub- 

 tile matter called rather, it seems more reasonable to ascribe the mutual 

 attraction of bodies to an action which the aether exercises upon them, 

 though its manner of acting may be unknown to us, than to have re- 

 course to an unintelligible property As the idea of all 



occult qualities is now banished from philosophy, attraction ought not 

 to be considered in this sense." t 



It does not appear how so vague and inexplicable a supposition is 

 calculated to commend itself " to those who are fond of clear principles 

 in philosophy." In his anxiety to avoid an "occult quality " in matter, 

 this learned writer seems quite unconscious of the fact that by investing 

 his aether with an "unknown manner of acting," he is just as fatally "hav- 

 ing recourse to an unintelligible property." Certainly, just as " perplex- 



*Letters, &c. Let. 54, 7th September, 1760. 

 t Letters, &c. Let. 68, 18th October, 17G0. 



