Experimental researches in electricity. Vol. 3 / by Michael Faraday.

  • Michael Faraday
Date:
[1855?]
Catalogue details

Licence: Public Domain Mark

Credit: Experimental researches in electricity. Vol. 3 / by Michael Faraday. Source: Wellcome Collection.

    21/612 (page 9)
    2174. Next, we may observe, that bodies that are exceedingly different to each other in chemical, physical, and mechanical properties, develope this effect; for solids and liquids, acids, alkalies, oils, water, alcohol, asther, all possess the power. 2175. And lastly, we may observe, that in all of them, though the degree of action may differ, still it is always the same in kind, being a rotative power over the ray of light; and further, the direction of the rotation is, in every case, independent of the nature or state of the substance, and dependent upon the direc- tion of the magnetic line of force, according to the law before laid down (2160.). 2176. Amongst the substances in which this power of action is found, I have already distinguished the silico-borate of lead (2151.) as eminently fitted for the purpose of exhibiting the phas- nomena. I regret that it should be the best, since it is not likely to be in the possession of many, and few wdll be induced to take the trouble of preparing it. If made, it should be well annealed, for otherwise the pieces will have considerable power of depolarizing hght, and then the particular phaenomena under consideration are much less stinkingly observed. The borate of lead, however, is a substance much more fusible, softening at the heat of boiling oil, and therefore far more easily prepared in the form of glass plates and annealed; and it possesses as much magneto-rotative power over light as the silico-borate itself. Flint-glass exhibits the property, but in a less degree than the substances above. Crown-glass show's it, but in a still smaller degree. 2177. Whilst employing crystalline bodies as diamagnetics, I generally gave them that position in w-hich they did not affect the polarized ray, and then induced the magnetic curves through them. As a class, they seemed to resist the assumption of the rotating state. Rock-salt and fluor-spar gave evidence of the power in a slight degree j and I think that a crystal of alum did the same, but its ray length in the transparent part was so small that I could not ascertain the fact decisively. Tw'o spe- cimens of transparent fluor, lent me by Mr. Tennant, gave the effect. 2178. Rock-crystal, 4 inches across, gave no indications of action on the ray, neither did smaller crystals, nor cubes about three-fourths of an inch in the side, which were so cut as to