The result of this important experiment was communicated to the Royal Society by Dr. Faraday on the 27th November, 1845, the enunciation of the fact by this learned philosopher being, "that when '_the line of magnetic force_' is made to pass through certain transparent bodies parallel to a ray of polarized light traversing the same body, the ray of polarized light experiences a rotation." Now, "_the line of magnetic force_" means that continual flow of the magnetic current which passes from pole to pole, and is indicated by iron filings sprinkled on paper placed above the poles of a magnet, and usually termed _magnetic curves_, or the curved lines of magnetic force. (Fig. 241.) [Illustration: Fig. 241. The curved lines of magnetic force.] The heavy glass already alluded to, upon which the magnet exerts a certain influence, is called THE DIA-MAGNETIC; and by this term is meant a body through which the lines of magnetic force are passing without affecting it like iron or steel. At page 212 is a picture representing (at Figs. 201 and 202) the direction of the electricity and that of the magnetic current or whirl at right angles to it. If, then, Fig. 202 be considered as a piece of glass, the arrow A B [Page 248] will show "the line of magnetic force," the point B being the north pole, and the shaft A the south pole of the magnet, and the arrows traced round will represent direction. This simple drawing expresses the whole of the law of the action of the magnet on the glass, and if kept in view, will give every position and consequence of direction resulting from it. The phenomenon of the affection of the beam of polarized light is immediately connected with the magnetic force, and this is supposed to be proved by the _brightness_ of the polarized ray being developed _gradually_, as the iron coiled with wire requires about two seconds to acquire its greatest power after being connected with the battery.