OF NATURAL PHILOSOPHY. 201 



that it is capable of including. (See 171.) It 

 is the verification of such inductions which con- 

 stitutes theory in its largest sense, and which- 

 embraces an estimation of the influence of all such 

 circumstances as may modify the effect of the 

 cause whose laws of action we have arrived at and 

 would verify. To return to our example : particular 

 inductions drawn from the motions of the several 

 planets about the sun, and of the satellites round 

 their primaries, &c. having led us to the general 

 conception of an attractive force exerted by every 

 particle of matter in the universe on every other 

 according to the law to which we attach the 

 name of gravitation ; when we would verify this 

 induction, we must set out with assuming this law, 

 considering the whole system as subjected to its 

 influence and implicitly obeying it, and nothing in- 

 terfering with its action ; we then, for the first time, 

 perceive a train of modifying circumstances which 

 had not occurred to us when reasoning upwards from 

 particulars to obtain the fundamental law ; we per- 

 ceive that all the planets must attract each other, 

 must therefore draw each other out of the orbits 

 which they would have if acted on only by the sun ; 

 and as this was never contemplated in the inductive 

 process, its validity becomes a question, which can 

 only be determined by ascertaining precisely how 

 great a deviation this new class of mutual actions 

 will produce. To do this is no easy task, or rather, 

 it is the most difficult task which the genius of man 

 has ever yet accomplished: still, it has been accom- 

 plished by the mere application of the general laws 

 of dynamics ; and the result (undoubtedly a most 



