PROGRESSIVE EFFECTS. 365 



more, without ever bringing them back to what they were at any formei- 

 time. The planet would then have moved in a parabola, or an hyperbola, 

 curves not returning into themselves. The quantities of the two forces were, 

 however, originally such, that the successive reactions of the effect bring back 

 the causes, after a certain time, to what they were before; and from that time 

 all the variations continued to recur again and again in the same periodical 

 order, and must so continue while the causes subsist and are not counteracted. 



§ 3. In all cases of progressive effects, whether arising from the accumu- 

 lation of unchanging or of changing elements, there is a uniformity of suc- 

 cession not merely between the cause and the effect, but between the first 

 stages of the effect and its subsequent stages. That a body ^w vacuo falls 

 sixteen feet in the first second, forty-eight in the second, and so on in the 

 ratio of the odd numbers, is as much a uniform sequence as that when the 

 supports are removed the body falls. The sequence of spring and summer 

 is as regular and invariable as that of the approach of the sun and spring ; 

 but we do not consider spring to be the cause of summer ; it is evident 

 that both are successive effects of the heat received from the sun, and that, 

 considered merely in itself, spring might continue forever without having the 

 slightest tendency to produce summer. As we have so often remarked, not 

 the conditional, but the unconditional invariable antecedent is termed the 

 cause. That which would not be followed by the effect unless something 

 else had preceded, and which if that somethng else had preceded, would 

 not have been required, is not the cause, however invariable the sequence 

 may in fact be. 



It is in this way that most of those uniformities of succession are gen- 

 erated, which are not cases of causation. When a phenomenon goes on 

 increasing, or periodically increases and diminishes, or goes through any 

 continued and unceasing process of variation reducible to a uniform rule 

 or law of succession, we do not on this account presume that any two suc- 

 cessive terms of the series are cause and effect. We presume the contrary ; 

 we expect to find that the whole series originates either from the continued 

 action of fixed causes or from causes which go through a corresponding proc- 

 ess of continuous change. A tree grows from half an inch high to a hun- 

 dred feet; and some trees will generally grow to that height unless pre- 

 vented by some counteracting cause. But we do not call the seedling the 

 cause of the full-grown tree; the invariable antecedent it certainly is, and 

 we know very imperfectly on what other antecedents the sequence is contin- 

 gent, but we are convinced that it is contingent on something ; because the 

 homogeneousness of the antecedent with the consequent, the close resem- 

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

 graduality of the growth, so exactly resembling the progressively accumu- 

 lating effect produced by the long action of some one cause, leave no possi- 

 bility of doubting that the seedling 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 repetition of certain processes of nutri- 

 tion, the rise of the sap, the absorptions and exhalations by the leaves, etc. ; 

 and the same experiments would probably prove to us that the growth of 

 the tree is the accumulated sum of the effects of these continued processes, 

 were we not, for want of sufficiently microscopic eyes, unable to observe 

 correctly and in detail what those effects are. 



