ATTRACTION. 137 



SEC. IV. ATTRACTION.* 



By attraction, we mean the tendency of bodies to approximate, and 

 also the unknown cause of that tendency. In its most general sense, 

 it extends to atoms and masses reciprocally, and to every distance. 



It is the bond of the universe.; it appears to depend in general on no 

 proximate cause, but to emanate at once from the will of the Deity. 



Counteracted and modified by the powers of repulsion and pro- 

 jection, it keeps every thing in harmonious equilibrium. 



It is unknown whether it arises, in all its varieties, from the modifi- 

 cations of one cause, or whether there are several, giving origin to the 

 different kinds of attraction. 



However this may be, it is most convenient to consider the sub- 

 ject under different heads. 



1. GRAVITATION. 



2. MAGNETISM. 



3. GALVANIC ELECTRICITY. 



4. COHESION AND AGGREGATION. 



5. CHEMICAL ATTRACTION OR AFFINITY. 



1. GRAVITATION. 



(a.) It extends to every thing, to all quantities of matter, and to 

 all distances. 



(6.) Its force is directly as the quantity of matter, and inversely as 

 the square of the distance. The quantity of matter, in different 

 cases, being as 1.2. 3. 4, the attracting force at a given distance, will 

 be as those numbers directly ; but the same body being placed suc- 

 cessively at the distances 1. 2. 3.4, the attracting force will be ex- 

 pressed inversely, by 1. 4. 9. 16, that is, at the distance 2 it will be 

 J, at 3, i, and at 4, ,',,, as great as it was at the distance 1. 



We are familiar with the effects of gravitation, and therefore re- 

 gard them as natural ; they are so to our habits, but only in obedi- 

 ence to an established law ; if the law had been different, our habits 

 would have been accommodated to it. 



Were there no attraction towards the earth, a stone thrown into the 

 air would not return, and would stop only from the resistance of some 

 medium, or of some other body which it might encounter. 



(c.) The projectile power modifies the gravitating force, so that 

 the planets move in elliptical orbits, and neither fall to the centre of 

 motion, nor move off in tangents to the curve of the orbit. 



* I have been accustomed to give, in my lectures, a very general sketch of the 

 different varieties of attraction, that affinity may be the better understood, and shall 

 pursue the same course in this work. 



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