CHEMICAL AFFINITY. 133 



it is mutual ; that it extends to indefinite distances ; and that all 

 bodies, as far as is known, are possessed of it. 



3. When two bodies are brought within a certain distance, they 

 adhere together, and require a considerable force to separate 

 them. This is the case, for instance, with two polished pieces of 

 marble or glass. When a piece of metal, or indeed almost any 

 body whatever, is plunged into water and drawn out again, its 

 surface is moistened, that is to say, part of the water adheres to 

 it. When a rod of gold is plunged into mercury, it comes out 

 stained indelibly with a white colour, because it retains and carries 

 with it a portion of the mercury. Hence it is evident that there 

 is a force which urges these bodies towards each other, and keeps 

 them together ; consequently there is an attraction between them. 

 Bodies, therefore, are not only attracted towards the earth and 

 the planetary bodies, but towards each other. The nature of this 

 attraction cannot be assigned any more than that of gravitation ; 

 but its existence is equally certain, as far at least as regards by far 

 the greater number of bodies. 



4. In all cases we find the particles of matter united together in 

 masses ; differing indeed from each other in magnitude, but con- 

 taining all of them a great number of particles. These particles 

 remain united, and cannot be separated without the application of 

 a considerable force ; consequently they are kept together by a 

 force which urges them towards each other, since it opposes their 

 separation. Consequently this force is an attraction. 



Thus we see that there is a certain unknown force which urges 

 bodies towards each other ; a force which acts not only upon large 

 masses of matter, as the sun and the planets, but upon the smaller 

 component parts of these bodies, and even upon the particles of 

 which these bodies are composed. Attraction, therefore, as far as 

 we know, extends to all matter, and exists mutually between all 

 matter. It is not annihilated at how great a distance soever we 

 may suppose bodies to be placed from each other; neither does it 

 disappear, though they be placed ever so near each other. The 

 nature of this attraction, or the cause which produces it, is alto, 

 gether unknown ; but its existence is demonstrated by all the 

 phenomena of nature. 



5. This attrac ion was long accounted for, by supposing that 

 there existed a certain unknown substance, which impelled all 

 bodies towards each other; a hypothesis to which philosopher* 



Kl 



