358 INDUCTION. 



it, was not more an inductive act than that of our 

 supposed navigator. 



The object of Kepler was to determine the real 

 path described by each of the planets, or let us say 

 the planet Mars, (for it was of that body that he first 

 established two of the three great astronomical truths 

 which bear his name) . To do this there was no other 

 mode than that of direct observation : and all which 

 observation could do was to ascertain a great number 

 of the successive places of the planet ; or rather, of 

 its apparent places. That the planet occupied succes- 

 sively all these positions, or at all events, positions 

 which produced the same impressions on the 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 instru- 

 ments, 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 joined 

 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 from being as easy as that of the navigator 

 who expressed the series of his observations on suc- 

 cessive points of the coast by the general conception 

 of an island. But it is the very same sort of opera- 

 tion ; and if the one is not an induction but a descrip- 

 tion, this must also be true of the other. 



To avoid misapprehension, we must remark that 

 Kepler, in one respect, performed a real act of induc- 

 tion ; namely, in concluding that because the observed 

 places of Mars were correctly represented by points 

 in an imaginary ellipse, therefore Mars would con- 

 tinue to revolve in that same ellipse ; and even in 



