OBSERVATION AND DESCRIPTION. 191 



being in an ellipse. We conclude that the remaining effects, 

 the places which have not been observed, agree in the same 

 circumstance, and that the law of the motion of the earth is 

 motion in an ellipse. 



The Colligation of Facts, therefore, by means of hypo- 

 theses, or, as Dr. Whewell prefers to say, by means of Concep- 

 tions, instead of being, as he supposes, Induction itself, takes 

 its proper place among operations subsidiary to Induction. 

 All Induction supposes that we have previously compared the 

 requisite number of individual instances, and ascertained in 

 what circumstances they agree. The Colligation of Facts is 

 no other than this preliminary operation. When Kepler, 

 after vainly endeavouring to connect the observed places of a 

 planet by various hypotheses of circular motion, at last tried 

 the hypothesis of an ellipse and found it answer to the 

 phenomena ; what he really attempted, first unsuccessfully and 

 at last successfully, was to discover the circumstance 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 different planets, by the proposition 

 that the squares of the times are proportional to the cubes 

 of the distances, what he did was simply to ascertain the pro- 

 perty in which the periodic times of all the different planets 

 agreed. 



Since, therefore, all that is true and to the purpose in 

 Dr. Whewell's doctrine of Conceptions might be fully ex- 

 pressed by the more familiar term Hypothesis; and since 

 his Colligation of Facts by means of appropriate Concep- 

 tions, is but the ordinary process of finding by a comparison 

 of phenomena, in what consists their agreement or resem- 

 blance; I would willingly have confined myself to those 

 better understood expressions, and persevered to the end in 

 the same abstinence which I have hitherto observed from 

 ideological discussions; considering the mechanism of our 

 thoughts to be a topic distinct from and irrelevant to the 

 principles and rules by which the trustworthiness of the 

 results of thinking is to be estimated. Since, however, a 

 work of such high pretensions, and, it must also be said, of 



