192 



INDUCTION. 



of the planets, or let us say by the 

 planet Mars (since it was of that body 

 that he fii^t established the two of 

 his three laws which did not require 

 a comparison of planets). To do this 

 there was no other mode than that of 

 direct observation ; and all which ob- 

 servation could do was to ascertain a 

 great number of the successive places 

 of the planet, or rather, of its ap- 

 parent places. That the planet occu- 

 pied successively all these positions, 

 or at all events, positions which pro- 

 duced the same impressions on the 

 eye, and that it passed from one of 

 these to another insensibly, and with- 

 out any apparent breach of continuity ; 

 thus much the senses, with the aid of 

 the proper instruments, could ascer- 

 tain. What Kepler did more than 

 this, was to find what sort of a curve 

 these different points would make, 

 supposing them to be all joined to- 

 gether. He expressed the whole 

 series of the observed places of Mars 

 by what Dr. Whewell calls the gene- 

 ral conception of an ellipse. This 

 operation was far from being as easy 

 as that of the navigator who expressed 

 the series of his observations on suc- 

 cessive ])oints 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. 



The only real induction concerned 

 in the case consisted in inferring that 

 because the observed places of Mars 

 were correctly represented by points 

 in an imaginary ellipse, therefore 

 Mars would continue to revolve in 

 that same ellipse ; and in concluding 

 (before the gap had been filled up by 

 further observations) that the posi- 

 tions of the planet during the time 

 which intervened between two obser- 

 vations, must have coincided with the 

 intermediate points of the curve. For 

 these were facts which had not been 

 directly observed. They were in- 

 ferences from the observations ; facts 

 inferred, as distinguished from facts 

 seen. But these inferences were so 



far from being a part of Kepler's 

 philosophical operation, that they had 

 been drawn long before he was bom. 

 Astronomers had long known that 

 the planets periodically returned to 

 the same places. Wlien this had been 

 ascertained, there was no induction 

 left for Kepler to make, nor did he 

 make any further induction. He 

 merely applied his new conception to 

 the facts inferred, as he did to the 

 facts observed. Knowing already 

 that the planets continued to move in 

 the same paths ; when he found that 

 an elli]^)se correctly represented the 

 past path he knew that it would repre- 

 sent the future path. In finding a com- 

 pendious expression for the one set 

 of facts he found one for the other : 

 but he found the expression only, not 

 the inference ; nor did he (which is 

 the true test of a general truth) add 

 anything to the power of predictioxi 

 already possessed 



§4. The descriptive operation which 

 enables a number of details to be 

 summed up in a single proposition, 

 Dr. Whewell, by an aptly chosen ex- 

 pression, has termed the Colligation 

 of Facts. In most of his observations 

 concerning that mental process I full}' 

 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 re- 

 ceived meaning of the term, is not in- 

 duction at all, as the type of induction 

 generally ; and laying down, through- 

 out his work, as principles of induction, 

 the principles of mere colligation. 



Dr. Whewell maintains that the 

 general proposition which binds to- 

 gether the particular facts, and makes 

 them, as it were, one fact, is not the 

 mere sum of those facts, but some- 

 thing more, since there is introduced 

 a conception of the mind, which did 

 not exist in the facts themselves. 

 "The particular facts," says he,* " are 

 not merely brought together, but there 



* Novum Orffanuvi Renovatuvi, pp. 72, 73. 



