1-16 



Atoms to be 

 considered as 

 separate. 



Improper 

 use of the term 

 density. 



Atmospheres. 



Mistake of 

 another au- 

 thor. 



ON GUAVITATlOlSr. 



law of the density, as well as that of the force, must be sup- 

 posed to change at the sLwface of every material body, long- 

 before — can becoms equal to P. 



Professor Vince's " two independent circumstances" are 

 both dependent on the supposition of the external action of 

 the medium on a material aggregate of considerable mag- 

 nitude, which it never could have been in the contemplation 

 of Newton to advance: it would be idle to maintain the pos- 

 sibility of the hypothesis on any other ground, than that of 

 the independent action of the medium on every atom of 

 matter. Here tlierefore he is fighting with a shadow, and 

 not with " the vaunting assertions and errours of Mr. D." 



It is difficult to perceive the " necessity" of employing 

 the term density, in order to convey the idea of the square 

 of the cube root of the density, simply because this was the 

 poiver of the density that was required for the author's pur- 

 pose. The density of light or heat diverging from a centre 

 in the form of projected corpuscles, may be ver}' justly esti- 

 mated by the number of particles faUing on a given surface, 

 for this simple reason, that their number is here a true mea- 

 sure of the density; while in the case of an elastic medium 

 it is not a true measure. 



The idea of the interference of different atmospheres must 

 be considered as in some measure foreign to the question, 

 since only one general ethereal medium of variable density 

 is supposed to be concerned, and since the modifications of 

 this medium, produced by the several celestial bodies, might 

 easily coexist without any material interference or interrup- 

 tion. 



1 must beg leave to observe, on the other hand, that ano- 

 ther modern author appears to me to have been somewhat 

 too hasty in asserting, that the law of gravitation may be 

 derived from the supposition of an elastic medium, repelled 

 by a force which varies inversely as the distance. If I am 

 not mistaken, such a force would produce, according to the 

 common laws of the operation of forces, a medium varying 

 in density as some given power of the distance, and an ap- 

 parent attraction increasing with the distance of the material 

 bodies coucerncd. 



I have 



