ATTRACTION. 



hud discovered ; but left the complete 

 development of its consequences to the 

 geometers that should succeed him. 



The profound analysis also, of which he 

 was the inventor, had not been sufficient- 

 ly perfected, to enable him to give com- 

 plete solutions to all the difficult problems 

 which arise, in considering the theory of 

 the system of the world ; so that he was 

 oftentimes obliged to give only imperfect 

 sketches or approximations, and leave 

 them to be verified by a more rigorous 

 calculation. 



Attraction may be divided, with respect 

 to the law it observes, into two kinds ; 1. 

 That which extends to sensible distances ; 

 such is the attraction of gravity, of which 

 we have been treating, which is found in 

 all bodies, and the attraction of magne- 

 tism and of electricity found in some par- 

 ticular bodies : 2. That which extends to 

 very small or insensible distances. 



The attractions belonging to the first 

 class must be as numerous as there are 

 bodies situated at sensible distances. It 

 has been proved that their intensity varies 

 with the mass and the distance of the at- 

 tracting bodies ; it increases with the mass 

 of those bodies, but diminishes as the dis- 

 tance between them increases. 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. 



The nature of the attraction of gravity 

 has been already discussed. It is, as far 

 as the experience of man can extend, uni- 

 versal in all matter. The attractions of 

 magnetism and of electricity 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 ; and there is good 

 reason to suspect that the magnetism of 

 the three latter substances is caused by 

 their containing some iron united to them. 



The intensity of these three attractions 

 increases as the mass of the attracting bo- 

 dies, and diminishes as the square of the 

 distance. 



The first extends to the greatest dis- 

 tance at which bodies are known to be se- 

 parated from each other. How far elec- 

 tricity extends has not been ascertained ; 

 but magnetism extends at least so far as 

 the semidiameterof the earth. All bodies 

 possess gravity ; but it has been suppos- 

 ed that the other two attractions are con- 

 fined to two or three subtile fluids, which 

 constitute a part of all those bodies that 



exhibit the attractions of magnetism or of 

 electricity. 



If we compare the different bodies act- 

 ed on by gravitation, we shall find that 

 the absolute force of their gravitation is 

 in all cases the same, provided their dis- 

 tances from each other, and their mass, 

 be the same ; but this is by no means the 

 case with electrical and magnetic bodies : 

 in them, the forces by which they are at- 

 tracted towards each other are exceed- 

 ingly various, even when the mass and 

 the distance are the same. Sometimes 

 these forces disappear almost entirely; 

 at other times they are exceedingly in- 

 tense. 



Gravity, therefore, is a force inherent 

 in bodies ; electricity and magnetism not 

 so ; a circumstance which renders the 

 opinion of their depending on peculiar 

 fluids extremely probable. If we com- 

 pare the absolute force of these three 

 powers with each other, it would appear 

 that the intensity of the two last, every 

 thing else being equal, is greater than 

 that of the first; but their relative inten- 

 sity cannot be compared, and is therefore 

 unknown. Hence it follows that these 

 different attractions, though they follow 

 the same laws of variation, are not the 

 same in kind. 



The attractions between bodies at in- 

 sensible distances have been distinguish- 

 ed by the name of affinity, while the term 

 attraction has been more commonly con- 

 fined to cases of sensible distance. 



Affinity may be considered as operat- 

 ing on homogeneous or heterogeneous 

 substances. Homogeneous affinity urges 

 substances of the same nature together, 

 as iron to iron, soda to soda. Hetero- 

 geneous affinity draws substances of dif- 

 ferent, natures into union, as acid and al- 

 kalies. 



Homogeneous affinity is usually deno- 

 minated cohesion, and sometimes adhe- 

 sion, when the surfaces of bodies are on- 

 ly referred to ; it is nearly universal ; as 

 far as is known, caloric and light alone are 

 destitute of it. 



Heterogeneous affinity is the cause of 

 the formation of compound substances ; 

 thus muriatic acid unites with soda, and 

 forms sea-salt ; and sea-salt in saturated 

 solution is united into masses by homoge- 

 neous affinity. Heterogeneous affinity is 

 universal as far as is known ; that is to 

 say, there is no substance which is not 

 attracted by some other substance. It is 

 generally taken for granted, that every 

 substance has more or less affinity for all 

 others, though it is certainly assuming 

 more than even analogy can warrant, sand 



