190 OPERATIONS SUBSIDIARY TO INDUCTION. 



of induction : no other exposition can be given of that logical 

 operation. That he is wrong in the latter assertion, the whole 

 of the preceding hook has, I hope, sufficiently proved; and 

 that the process by which the ellipticity of the planetary orbits 

 was ascertained, is not induction at all, was attempted to be 

 shown in the second chapter of the same book.* We are now, 

 however, prepared to go more into the heart of the matter 

 than at that earlier period of our inquiry, and to show, not 

 merely what the operation in question is not, but what it is. 



4. We observed, in the second chapter, that the pro- 

 position "the earth moves in an ellipse/' so far as it only 

 serves for the colligation or connecting together of actual 

 observations, (that is, as it only affirms that the observed 

 positions of the earth may be correctly represented by as 

 many points in the circumference of an imaginary ellipse,) is 

 not an induction, but a description : it is an induction, only 

 when it affirms that the intermediate positions, of which there 

 has been no direct observation, would be found to correspond 

 to the remaining points of the same elliptic circumference. 

 Now, though this real induction is one thing, and the descrip- 

 tion another, we are in a very different condition for making 

 the induction before we have obtained the description, and 

 after it. For inasmuch as the description, like all other 

 descriptions, contains the assertion of a resemblance between 

 the phenomenon described and something else; in pointing 

 out something which the series of observed places of a planet 

 resembles, it points out something in which the several places 

 themselves agree. If the series of places correspond to as 

 many points of an ellipse, the places themselves agree in being 

 situated in that ellipse. We have, therefore, by the same 

 process which gave us the description, obtained the requisites 

 for an induction by the Method of Agreement. The succes- 

 sive observed places of the earth being considered 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 



* Supra, book iii. ch. ii. 3, 4, 5. 



