444 Action of a Galvanic Coil on an external small Magnet, 



rheophore acts as a sheet or shell of positive and negative mag- 

 netic matter enclosed by the circuit leads to the same law, it fol- 

 lows that the a priori theory gives a reason for that hypothesis. 

 Besides, from a consideration of the modes of the direct and in- 

 direct actions of the coil discussed in arts. 45-52, it would seeni 

 that the hypothesis is applicable with more exactness to the action 

 of a coil than to that of a magnet. 



78. Since, therefore,, the hydrodynamical theory has given a 

 reason for the empirical hypothesis on which the formula and 

 calculations referred to in art. 76 are founded, and has also ac- 

 counted for all the experimental facts from which Ampere^s 

 theory is deduced, I think I am entitled to say that, so far as the 

 comparison of calculated results with experiment is satisfactory, 

 it is to be regarded as confirmatory of the hydrodynamical theory. 

 At the same time, as I have indicated in art. 53, and proved 

 in the Postscript to Part II., that theory admits of being com- 

 pared with experiment quite apart from any reference to Am- 

 pere's theory. 



In concluding this communication, I feel justified in express- 

 ing the opinion that the arguments in Parts L, II., and III. suffice 

 for concluding that the theoretical explanation of galvanic and 

 magnetic phenomena is to be sought for by means of mathema- 

 tical deductions from the fundamental principles enunciated in 

 art. 1 — and that, in so far as the present essay has been success- 

 ful in this respect, it carries with it the whole of the theoretical 

 philosophy I have laboured so many years to uphold and ad- 

 vance, which I consider to be, in fact, the only legitimate exten- 

 sion of the Newtonian philosophy. It has sometimes been said 

 that Ampere is the Newton of galvanic and magnetic physics. 

 But since Ampere himself professes that he makes deductions 

 exclusively from experiment, he ought rather to be compared 

 with Kepler than with Newton. After all that he did, there 

 remained to be attempted in general physics the performance of 

 the ; part analogous to that in physical astronomy which was 

 begun by Newton and has since been so successfully carried on. 

 It is moreover to be said that the foundation of the science of 

 theoretical physics is laid in Newton's Principia, this work being 

 by no means confined to physical astronomy, but comprehending 

 the principles of all departments of natural philosophy which 

 have relation to the laws of action of physical force. It has been 

 in conformity with rules and principles of philosophy that New- 

 ton laid down, and for the purpose of applying them in researches 

 respecting the physical forces and the constitution of bodies 

 which the state of science in his day did not allow of undertaking, 

 that my efforts have been made in the department of theoretical 

 physics ; and I now take occasion to state that the main con- 



