202 DISCOURSE ON THE STUDY 



beautiful and satisfactory one) is, that all those 

 observed deviations in the motions of our system 

 which stood out as exceptions ( 154.), or were 

 noticed as residual phenomena and reserved for 

 further enquiry ($ 158.), in that imperfect view of 

 the subject which we got in the subordinate process 

 by which we rose to our general conclusion, prove 

 to be the immediate consequences of the above-men- 

 tioned mutual actions. As such, they are neither 

 exceptions nor residual facts, but fulfilments of 

 general rules, and essential features in the state- 

 ment of the case, without which our induction would 

 be invalid, and the law of gravitation positively un- 

 true. 



(214-.) In the theory of gravitation, the law is all 

 in all, applying itself at once to the materials, and 

 directly producing the result. But in many other 

 cases we have to consider not merely the laws which 

 regulate the actions of our ultimate causes, but a 

 system of mechanism, or a structure of parts, through 

 the intervention of which their effects become 

 sensible to us. Thus, in the delicate and curious 

 electro-dynamic theory of Ampere, the mutual 

 attraction or repulsion of two magnets is referred 

 to a more universal phenomenon, the mutual action 

 of electric currents, according to a certain funda- 

 mental law. But, in order to bring the case of a 

 magnet within the range of this law, he is obliged 

 to make a supposition of a peculiar structure or 

 mechanism, which constitutes a body a magnet, 

 viz. that around each particle of the body there 

 shall be constantly circulating, in a certain stated 

 direction, a small current of electric fluid. 



