2 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIX.) 
words, are so directly related and mutually dependent, that they are convertible, as it 
were, one into another, and possess equivalents of power in their action*. In modern 
times the proofs of their convertibility have been accumulated to a very considerable 
extent, and a commencement made of the determination of their equivalent forces. 
214/. This strong persuasion extended to the powers of light, and led, on a former 
occasion, to many exertions, having for their object the discovery of the direct rela- 
tion of light and electricity, and their mutual action in bodies subject jointly to their 
power-f' ; but the results were negative and were afterwards confirmed, in that 
respect, by Wartmann^;. 
2148. These ineffectual exertions, and many others which were never published, 
could not remove my strong persuasion derived from philosophical considerations ; 
and, therefore, I recently resumed the inquiry by experiment in a most strict and 
searching manner, and have at last succeeded in magnetizing and electrifying a ray 
of light , and in illuminating a magnetic line of force. These results, without entering 
into the detail of many unproductive experiments, I will describe as briefly and 
clearly as I can. 
2149. But before I proceed to them, I will define the meaning I connect with 
certain terms which I shall have occasion to use : — thus, by line of magnetic force, or 
magnetic line of force, or magnetic curve, I mean that exercise of magnetic force 
which is exerted in the lines usually called magnetic curves, and which equally 
exist as passing from or to magnetic poles, or forming concentric circles round an 
electric current. By line of electric force, I mean the force exerted in the lines 
joining two bodies, acting on each other according to the principles of static electric 
induction (1161, &c.), which may also be either in curved or straight lines. By a 
diamagnetic, I mean a body through which lines of magnetic force are passing, and 
which does not by their action assume the usual magnetic state of iron or loadstone. 
2150. A ray of light issuing from an Argand lamp, was polarized in a horizontal 
plane by reflection from a surface of glass, and the polarized ray passed through a 
Nichols eye-piece revolving on a horizontal axis, so as to be easily examined by the 
latter. Between the polarizing mirror and the eye-piece, two powerful electro-magnetic 
poles were arranged, being either the poles of a horse-shoe magnet, or the contrary 
poles of two cylinder magnets ; they were separated from each other about two 
inches in the direction of the line of the ray, and so placed, that, if on the same side 
of the polarized ray, it might pass near them ; or, if on contrary sides, it might go 
between them, its direction being always parallel, or nearly so, to the magnetic lines 
of force (2149.). After that, any transparent substance placed between the two 
poles, would have passing through it, both the polarized ray and the magnetic lines 
of force at the same time and in the same direction. 
* Experimental Researches, 57, 366, 376, 877, 961, 2071. 
t Philosophical Transactions, 1834. Experimental Researches, 951-955. 
I Archives de l’Electricite, ii. pp. 596-600. 
