164 JAMES CLEHK MAXWELL 



liquid through a solid whoso boundary surface is tho 

 same as that of tho conductor, provided tho (low of 

 liquid Is properly proportioned to tho flow of elec- 

 tricity. 



These analogies refer to steady currents in which, 

 therefore, the flow at any point of the conductor does 

 not depend on the time. In Part 1 1. of his paper Max- 

 well deals with Faraday's electro-tonic state. Faraday 

 had found that when clmnyi'tt are produced in the mag- 

 netic phenomena surrounding a conductor, an electric 

 current is set up in the conductor, which continues so 

 long as the magnetic changes are in progress, but 

 which ceases when the magnetic state becomes steady. 



u Considerations of this kind led Professor Faraday to 

 connect with his discovery of the induction of electric current* 

 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 un- 

 disturbed, but any change in this state is indicated by a 

 current or tendency towards a current. To this state he gave 

 the nanio of the * Klectro-tonic State/ and although he after- 

 wards succeeded in OX plaining the phenomena which suggested 

 it by means of less hyjiothetical conceptions, he has on several 

 occasions hinted at the probability that some phenomena 

 might l>e 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 oidy for 

 want of exjverimental 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 arc not sullieicntly 

 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 



