SECOND PERIOD OF ELECTRICAL DISCOVERIES The first period of Faraday's electrical discoveries lasted ten years. In he found that he required rest, and it was not till 1845 that he entered on his second great period of research, in which he discovered the effect of magnetism on polarized light, and the phenomena of diamagnetism.
Faraday had for a long time kept in view the possibility of using a ray of polarized light as a means of investigating the condition of transparent bodies when acted on by electric and magnetic forces. He began to work on this problem in 1822, and returned to it repeatedly during the next 13 years. The first evi dence which he obtained of the rotation of the plane of polariza tion of light under the action of magnetism was in 1845, the trans parent substance being his own heavy glass. He began to work on Aug. 3o, 1845, on polarized light passing through electrolytes. After three days he worked with common electricity, trying glass, heavy optical glass, quartz, Iceland spar, all without effect, as on former trials. On Sept. 13 he worked with lines of magnetic force. Air, flint, glass, rock-crystal, calcareous spar were examined, but without effect.
Heavy glass was experimented with. It gave no effects when the same magnetic poles or the contrary poles were on opposite sides (as respects the course of the polarized ray), nor when the same poles were on the same side either with the constant or inter mitting current. But when contrary magnetic poles were on the same side there was an effect produced on the polarized ray, and thus magnetic force and light were proved to have relations to each other. This fact will most likely prove exceedingly fertile, and of great value in the investigation of the conditions of natural force.
On Nov. 6 he sent, in to the Royal Society the 19th series of his "Experimental Researches," in which the whole conditions of the phenomena are fully specified. The negative rotation in ferro magnetic media is the only fact of importance which remained to be discovered afterwards (by M. E. Verdet in 1856) .
But his work for the year was not yet over. On Nov. 3 a new horseshoe magnet came home, and Faraday immediately began to experiment on the action in the polarized ray through gases, but with no effect. The following day he repeated an experiment which had given no result on Oct. 6. A bar of heavy glass was suspended by silk between the poles of the new magnet. "When it was ar ranged, and had come to rest, I found I could affect it by the magnetic forces and give it position." By Dec. 6 he had sent in to the Royal Society the 2oth, and on Dec. 24 the 21st series of his "Researches," in which the properties of diamagnetic bodies are fully described. Thus these two great discoveries were elaborated, like his earlier one, in about three months. The dis covery of the magnetic rotation of the plane of polarized light, though it did not lead to such important practical applications as some of Faraday's earlier discoveries, has been of the highest value to science, as furnishing complete dynamical evidence that wherever magnetic force exists there is matter, portions of which are rotating about axes parallel to the direction of that force.
(See ELECTRICITY : Historical Introduction and MAGNETISM.) His published works were Chemical Manipulation, being In structions to Students in Chemistry (1st ed. 1827, 2nd 1830, 3rd 1842) ; Experimental Researches in Electricity, vols. i. and ii.
(1844 and ;' vol iii. ; vol. iii. Richard Taylor and William Francis (185 5) ; Experimental Researches in Chemistry and Physics ; Lectures on the Chemical History of a Candle (edit. by W. Crookes, 1861) ; On the Various Forces in Nature (edit. by W. Crookes, no date).
See J. Tyndall, Faraday as a Discoverer (1st ed. 1868, and ed. 187o) ; Bence Jones, The Life and Letters of Faraday (2 vols., 187o) ; J. H. Gladstone, Michael Faraday (1872) ; S. P. Thompson, Michael Fara day; his Life and Work (1898). (J. C. MA.; X.)