304 INDUCTION. 



in the effects. The causes, as they exist at any moment, having pro- 

 duced a certain motion, that motion, becoming itself a cause, reacts on 

 the causes, and produces a change in them. By altering the distance 

 and direction of the central body relatively to the planet, and the direc- 

 tion and quantity of the tangential force, it alters the elements which 

 determine the motion at the next succeeding instant. This change 

 renders the next motion sojnewhat different ; and this difference, by a 

 fresh reaction upon the causes, renders the next motion still more dif- 

 ferent, and so on. The original state of the causes might have been 

 such, that this series of actions modified by reactions woukLnot have 

 been periodical. The sun's action, and the original impelling force, 

 might have been in such a ratio to one another, that the reaction of the 

 effect would have been . such as to alter the causes more and more, 

 without ever bringing them back to what they were at any former 

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

 bola,' cui-ves 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 continue to recur again 

 and again in the same periodical order, and miist so continue while the 

 causes subsist and ^are not counteracted. 



§ 3^. In all cases of progi-essive effects, whether aiising from the ac- 

 cumulation of an unchanging or of changing elements, there is an uni- 

 formity of succession not merely between the cause and the eftect, but 

 between the first stages of the effect and its subsequent stages. That 

 a body in vactio falls sixteen feet in the first second, forty-eight in the 

 second, and so on in the ratio of the odd numbers, one, three, five, &c., 

 is as much an uniform sequence as that when the supports are removed 

 the body falls. The sequence of sjjring and summer is as regular and' 

 invariable as that of the approach of the sun and spring : but we do 

 not consider sju'ing to be the cause of summer, it is evident that they 

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

 cause did not exist, spring 'might continue for ever, without having 

 the slightest tendency to produce stimmer. As we have so often re- 

 marked, not the conditional, but the unconditional invariable antece- 

 dent, is termed the cause. That which would not be followed by the 

 effect unless something else had preceded, is not the cause, however 

 invariable the sequence may in fact be. 



. ■ It is in this way that most of these uniformities of succession are 

 generated', 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 

 an uniform nile or law of succession, we do not on this account presume 

 that any two successive tei-ms of the series are cause and effect. We 

 presume the conti-ary ; we expect to find that the whole series originates 

 either from the continued action of fixed causes or from causes which go 

 through a con-esponding process of continuous change. A tree grows 

 from half an inch high to mi hundred feet ; -and some trees will gener- 

 ally grow to that height unless prevented 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 

 upon what other antecedents the sequence is contingent, but we are 



