PROGRESSIVE EFFECTS. 37 



is contingent on something ; because the homogeneousness of 

 the antecedent with the consequent, the close resemblance of 

 the seedling to the tree in all respects except magnitude, and 

 the graduality of the growth, so exactly resembling the pro- 

 gressively accumulating effect produced by the long action of 

 some one cause, leave no possibility of doubting that the seed- 

 ling and the tree are two terms in a series of that description, 

 the first term of which is yet to seek. The conclusion is 

 further confirmed by this, that we are able to prove by strict 

 induction the dependence of the growth of the tree, and even 

 of the continuance of its existence, upon the continued repeti- 

 tion of certain processes of nutrition, the rise of the sap, the 

 absorptions and exhalations by the leaves, &o. ; and the same 

 experiments would probably prove to us that the growth of 

 the tree is the accumulated sum of the effects of these con- 

 tinued processes, were we not, for want of sufficiently micro- 

 scopic eyes, unable to observe correctly and in detail what those 

 effects are. 



This supposition by no means requires that the effect should 

 not, during its progress, undergo many modifications besides 

 those of quantity, or that it should not sometimes appear to 

 undergo a very marked change of character. This may be 

 either because the unknown cause consists of several component 

 elements or agents, whose effects, accumulating according to 

 different laws, are compounded in different proportions at 

 different periods in the existence of the organized being ; or 

 because, at certain points in its progress, fresh causes or 

 agencies come in, or are evolved, which intermix their laws 

 with those of the prime agent. 



