CHEMICAL AFFINITY. 135 



places, and which is always diminishing the distance between 

 bodies, unless when they are prevented from approaching each 

 other by some othrr force equally powerful. 



6. The change which attraction produces on bodies, is a dimi- 

 nution of their distance. Now the distances of bodies from each 

 other are of two kinds, either too small to be perceived by our 

 senses, or great enough to be easily perceived and estimated. In 

 the first case, the change of distance produced by attraction must 

 be insensible ; in the second case it must be visible. Hence the 

 attractions of bodies, as far as regards us, naturally divide them, 

 selves into two classes: 1. Those which act at sensible distances; 

 2. Those which act at insensible distances. The first class obviously 

 applies to bodies in masses of sensible magnitude ; the second class 

 must be confined to the particles of bodies, because they alone are 

 at insensible distances from each other. 



7. It has been demonstrated, that the intensity of the first class 

 of attractions varies with the mass and the distance of the attract, 

 ing bodies. It increases with the mass of these bodies, but dimi- 

 nishes as the distance between them increases. Hence we see that 

 hi this class of attractions every particle of the attracting bodies 

 act, since the sum of the attracting force is always proportional to 

 the number of particles in the attracting bodies. Why it dimi- 

 nishes as the distance increases, it is impossible to say ; but the 

 fact is certain, and is almost incompatible with the supposition of 

 impulsion as the cause of attraction. The rate of variation has 

 been demonstrated to be inversely as the square of the distance, in 

 all cases of attraction belonging to the first class. 



8. The attractions belonging to the first class must be as nume- 

 rous as there are bodies situated at sensible distances ; but it has 

 been ascertained that they may be all reduced to three different 

 kinds; namely, 1. Gravitation; 2. Electricity; 3. Magnetism. 

 The first of these has been shewn by Newton to belong to all 

 matter, as far as we have an opportunity of examining, and there, 

 fore to be universal. The other two are partial, being confined to 

 certain sets of bodies, while the rest of matter is destitute of them : 

 for it is well known, that all bodies are not electric, and that 

 scarcely any bodies are magnetic, except iron, cobalt, nickel, and 

 chromium. 



The intensity of these three attractions increases as the mass of 



R4 



