85 



ce are the same, or that existence in this case, 

 or junction in the other, are precisely the same, or produced by the 

 same causes, in the several examples. 



34. But, so far as the effect is common, the instances, how- 

 ever various their other properties might be, will be found to have 

 some common cause. Thus, a horse exists, and so does a tree; 

 but the causes which make the existence of the horse are not those 

 which make the existence of the tree; they are both examples of 

 existence, and the causes which produce mere existence are the 

 same; that is, they are in both existences. The same may be said 

 of the union of substances: different substances furnish alike in- 

 stances of the union of substances. If it be asked what is there in 

 common in the cause of union? it must be replied, a property in 

 the things united, the force of which is to produce their union. As 

 the effect, viz. an union of substances, is common in all the 

 examples, so also must the cause of the common effect be in all cases 

 identical. In opposition to this view, it may be urged, if the princi- 

 ple of union is identical in all cases, election among substances is 

 precluded, whereas the fact is otherwise; for the substances which 

 do unite are found to entertain, with respect to rach other, a par- 

 ticular and not a common or general relation. From this particu- 

 lar relation may be explained, why a property, to a certain extent 

 identical, in all the instances of union, gives rise to examples of 

 specific election. The property which produces the union of sub- 

 stances is no more elementary than any other agent, or form of 

 existence, but, like every thing else, is constituted ; one reason then 

 why some substances are disposed to unite with others, but not with 

 all, is that the causes of union exist variously in substances, and the 

 principle of union is thus formed only when the agreement of its 

 causes contained in the substances respectively subsists, so as to iden-r 

 tify the property, by supplying its causes in a way conformable with 

 the universal law of causation. Another reason why some substances 

 are disposed to unite with others, and not with all, may be found 

 in the modification to which the causes of union, existing in different 

 substances, are liable in common with all other causes. Hence it 

 appears that the property of union among substances is identical, 

 so far as the effect is common; that the difference of the principle 

 is expressed in the obvious modifications illustrated in the examples; 

 that the specific elections among substances depend first upon the 

 concurrence of the causes contained in the substances to form the 

 common property of union; and, second, upon a similar agreement 

 or concurrence of causes, when these causes are modified by allied 

 agents, resulting from particular and more complex relations. 



35. The varieties or modifications of the principle of union 

 are grossly classed in books under the titles, " gravitation, simple 

 attraction, attraction of cohesion, &c." But the varieties, or modi- 

 fications of identity in the causes of union, which are included in 

 this classification, are perhaps endless. The chymists have indi- 

 cated another class of these uniting agencies, agreeing with another 



