278 INDUCTION. 



same 



impressions on riie eye, and that it passed from one of these to 

 another insensibly, and without any apparent breach of continuity ; 

 thus much the senses, with the aid of the proper instruments, could 

 ascertain. What Kepler did more than this, was to find what sort of 

 a curve these different points would make, supposing them to be all 

 ioined together. He expressed the whole series of the observed 

 places of Mars by what Mr. Whewell calls the general conception of 

 an ellipse. This operation was far fi-om being as easy as that of the 

 navio-ator who expressed the series of his observations on successive 

 points of the coast by the general conception of an island. But it is 

 the very same sort of operation ; and if the one is not an induction but 

 a description, this must also be true of the other. 



To avoid misapprehension, we must remark that Kepler, in one 

 respect, performed a real act of induction; namely, in concluding that 

 because the observed places of Mars were correctly represented by 

 points in an imaginary ellipse, therefore Mars would continue^ to re- 

 volve in that same ellipse ; and even in concluding that the position of 

 the planet during the time which intervened between two observa- 

 tions, must have coincided with the intermediate points of the curve. 

 But this really inductive operation requires to be carefully distin- 

 guished from the mere act of bringing the facts actually observed 

 under a o-eneral description. So distinct are these two operations, 

 that the one might have been performed without the other. Men 

 mio-ht and did make correct indvictions concerning the heavenly mo- 

 tions, before they had obtained correct general descriptions of them. 

 It was known that the planets always moved in the same paths, long 

 before it had been ascertained that those paths were ellipses. Men 

 early remarked that the same set of apparent positions returned pe- 

 riodically. When they obtained a new description of the phenomenon, 

 they did not necessarily make any further induction, nor (which is the 

 true test of a new general ti'Uth) add anything to the power of predic- 

 tion which they already 



§ 4. The descriptive operation which enables a number of details to 

 be summed up in a single proposition, Mr. "Whewell, by an aptly- 

 chosen expression, has termed the Colligation of Facts.* In most of 

 his observations concerning that mental process I fully agree, and 

 would gladly transfer all that portion of his book into my own pages, 

 I only think him mistaken in setting up this kind of operation, which 

 according to the old and received meaning of the term is not induction 

 at all, as the type of induction generally; a,nd laying down, throughout 

 his work, as principles of induction, the principles of mere colligation. 



Mr. Whewell maintains that the general proposition which binds 

 to"-ether the particular facts and makes them, as it were, one fact, is 

 not the mere sum of those facts, but something more, since there is 

 introduced a conception of the mind, which did not exist in the facts 

 themselves. " The particular facts," says he,t " are not merely brought 

 to"-ether, but there is a new element added to the combination by the 

 ve!ry act of thought by which they are combined. . . .When the Greelvs, 

 after long observing the motions of the planets, saw that these motions 

 might be rightly considered as produced by the motion of one wheel 



• Philosophy of the Inductive Sciences, ii., 213, 214. t Ibid. 



