210 OPERATIONS SUBSIDIARY TO INDUCTION. 



something in which the several places themselves 

 agree. If the series of places corresponds to as 

 many points of an ellipse, the places themselves agree 

 in being situated in that ellipse. We have, therefore, 

 by means of the description, obtained the requisites 

 for an induction by the Method of Agreement. The 

 successive observed places of the earth being con- 

 sidered as effects, and its motion as the cause which 

 produces them, we find that those effects, that is, 

 those places, agree in the circumstance of being in an 

 ellipse. We conclude that the remaining effects, 

 the places which have not been observed, agree in 

 the same circumstance, and that ihe*law of the motion 

 of the earth is motion in an ellipse. 



The Colligation of Facts, therefore, by means of 

 hypotheses, or, as Mr. Whewell prefers to say, by 

 means of Conceptions, instead of being, as he sup- 

 poses, Induction itself, takes its proper place among 

 operations subsidiary to Induction. All Induction 

 supposes that we have previously compared the requi- 

 site number of individual instances, and ascertained 

 in what circumstances they agree ; the Colligation of 

 Facts is no other than this preliminary operation : 

 and the proper office of " clear and appropriate ideas,'* 

 on the necessity of which Mr. Whewell has said so 

 much, is to enable us to perform this operation cor- 

 rectly. When Kepler, after vainly endeavouring to 

 connect the observed places of a planet by various 

 hypotheses of circular motion, at last tried the hypo- 

 thesis of an ellipse and found it answer to the pheno- 

 mena, what he really attempted, first unsuccessfully 

 and at last successfully, was to discover the circum- 

 stance in which all the observed positions of the planet 

 agreed. And when he in like manner connected 

 another set of observed facts, the periodic times of the 



