Prof. Faraday on some Points of Magnetic Philosophy. 85 



the voltaic battery or any other sustaining source of an electric 

 current; — 4. Euler's idea of magnetic aethers or circulating fluids; 

 — 5. The strong conviction expressed by Sir Isaac Newton, that 

 even gravity cannot be carried on to produce a distant effect 

 except by some interposed agent* fulfilling the conditions of a 

 physical line, of force ; — 6. The example of the conflict and final 

 experimental settlement of the two theories of light. 



3306. I believe that the use by me of the phrase " places of 

 force " has been considered by some as objectionable, inasmuch 

 as it would seem to anticipate the decision that there are physical 

 lines of force. I will endeavour so to use it, if necessary, as not 

 to imply the assertion. Nevertheless I may observe, that we 

 use such a phrase in relation to a ray of light, even in those 

 parts of the ray where it is not extinguished, and where there- 

 fore we have no better knowledge of it or its existence than in 

 similar magnetic cases ; and we also use the phrase when speak- 

 ing of gravity in respect of places where no second body to gra- 

 vitate upon is present, and where, when existing, it cannot, 

 according to our present views, cause the gravitating force of the 

 primary body, or even the determination of it, upon that parti- 

 cular place. 



Magnetic polarity. 



3307. The meaning of this phrase is rapidly becoming more 

 and more uncertain. In the ordinary view, polarity does not 

 necessarily touch much upon the idea of lines of physical force ; 

 yet in the one natural truth it must either be essential to, and 

 identified with it, or else absolutely incompatible with, and 

 opposed to it. Coulomb's view makes polarity to depend upon 

 the resultant in direction of the action of two separated and dis- 

 tant portions of two magnetic fluids upon other like separated 

 portions, which are either originally separate, as in a magnet, or 

 are induced to separate, as in soft iron, by the action of the 

 dominant magnet ; — it is essential to this hypothesis that the 

 polarity force of one name should repel polarity force of the same 

 name and attract that of the other name. Ampere's view of 

 polarity is, that there are no magnetic fluids, but that closed 

 currents of electricity can exist round particles of matter (or 



* Newton says, " That gravity should be innate, inherent, and essential 

 to matter, so that one body may act upon another at a distance through a 

 vacuum, without the mediation of anything else, by and through which 

 their action and force may be conveyed from one to another, is to me so 

 great an absurdity, that I believe no man who has in philosophical matters 

 a competent faculty of thinking can ever fall into it. Gravity must be 

 caused by an agent acting constantly according to certain laws ; but whether 

 this agent be material or immaterial I have left to the consideration of my 

 readers." See the third letter to Bentlev. 



