fill. MICAL AFFINITY. 



the attracting bodies, and diminishes as the square of the distance 

 increases. The first extends to the greatest distance at which 

 bodies are known to be separated from each other. How far elec. 

 tricity extends has not beta ascertained ; but magnetism <-xtcnds 

 at least as far as the semidiameter of the earth. All bod 'CM possess 

 gravity ; but it has been supposed that the other two attractions 

 are confined to two or three subtile fluids, which constitute a part 

 of all those bodies which exhibit the attractions of electricity or 

 magnetism. This may be so ; but it is not, and scarcely can be 

 demonstrated. 



9. The absolute force of these attractions in given bodies can 

 only be measured by the force necessary to counteract the ellt-ct 

 of these attractions, or by the space which given bodies, acted on 

 merely by these attractions, traverse in a given time. If we 

 compare the different bodies acted on by gravitation, we shall find 

 that the absolute force of their gravitation towards each other is in 

 all cases the same, piovided their distances :-jn> 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 fhey 

 are attracted towards each other, called electricity and magnetism, 

 are exceedingly various, even when the mass and the ('istance are 

 the same. Sometimes these forces disappear almost entirely ; at 

 other times they are exceedingly intense. Gravity, therelore, is a 

 force inherent in bodies ; electricity and magnetism not .-o : a cir. 

 cumstance which renders the opinion of their depending upon 

 peculiar fluids exceedingly probable. If we compare the absolute 

 force of these three powers with each other, it would appear that 

 the intensity of the two last, every thing else being qual, is 

 greater than that of the first ; but their relative intensity 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. 



10. The attractions between bodies at insensible distances, and 

 which of course are confined to the particles of matter, have been 

 distinguished by the name of affinity ; while the term attraction 

 has been more commonly confined (o cases of sensible distance. 

 Now the particles of matter are two kinds, either homogeneous or 

 heterogeneous. By homogeneous particles, I mean particles which 

 compose the same body ; thus all particles of iron are homoge. 



