52 Mk maxwell, on FARADAY'S LINES OF FORCE. 



acts on the conductor and produces electric tension, or a continuous current, according as the 

 'circuit is open or closed. This current is produced only by changes of the electric or magnetic 

 phenomena surrounding the conductor, and as long as these are constant there is no observed 

 effect on the conductor. Still the conductor is in different states when near a current or 

 magnet, and when away from its influence, since the removal or destruction of the current or 

 magnet occasions a current, which would not have existed if the magnet or current had not 

 been previously in action. 



Considerations of this kind led Professor Faraday to connect with his discovery of the 

 induction of electric currents, the conception of a state into which all bodies are thrown by the 

 presence of magnets and currents. This state does not manifest itself by any known phenomena 

 as long as it is undisturbed, but any change in this state is indicated by a current or tendency 

 towards a current. To this state he gave the name of the " Electro-tonic State," and although 

 he afterwards succeeded in explaining the phenomena which suggested it by means of less 

 hypothetical conceptions, he has on several occasions hinted at the probability that some phe- 

 nomena might be discovered which would render the electro-tonic state an object of legitimate 

 induction. These speculations, into which Faraday had been led by the study of laws which 

 he has well established, and which he abandoned only for want of experimental data for the 

 direct proof of the unknown state, have not, I think, been made the subject of mathematical 

 investigation. Perhaps it may be thought that the quantitative determinations of the various 

 phenomena are not sufficiently rigorous to be made the basis of a mathematical theory ; 

 Faraday, however, has not contented himself with simply stating the numerical results of his 

 experiments and leaving the law to be discovered by calculation. Where he has perceived a law 

 he has at once stated it, in terms as unambiguous as those of pure mathematics ; and if the 

 mathematician, receiving this as a physical truth, deduces from it other laws capable of being 

 tested by experiment, he has merely assisted the physicist in arranging his own ideas, which 

 is confessedly a necessary step in scientific induction. 



In the following investigation, therefore, the laws established by Faraday will be assumed 

 as true, and it will be shewn that by following out his speculations other and more general 

 laws can be deduced from them. If it should then appear that these laws, originally devised 

 to include one set of phenomena, may be generalized so as to extend to phenomena of a different 

 class, these mathematical connexions may suggest to physicists the means of establishing 

 physical connexions ; and thus mere speculation may be turned to account in experimental 

 science. 



On Quantity and Intensity as Properties of Electric Currents. 



It is found that certain effects of an electric current are equal at whatever part of the 

 circuit they are estimated. The quantities of water or of any other electrolyte decomposed at two 

 different sections of the same circuit, are always found to be equal or equivalent, however 

 different the material and form of the circuit may be at the two sections. The magnetic 

 effect of a conducting wire is also found to be independent of the form or material of the wire 



