34 PROCEEDINGS OF THE AMERICAN ACADEMY 



Ampere's theory of magnetism. Science had been in possession of 

 voltaic electricity for forty years, its most powerful instruments had 

 been wielded by Davy, Hare, and Silliman, statical induction was 

 a familiar fact ; but it was reserved for Faraday first to see with his 

 own eyes the external influence of current electricity. Henry's induced 

 currents of the higher orders ; Page's devices for exalting the inten- 

 sity of induced currents, and their application to therapeutics ; Ruhm- 

 kortf 's coil, and its various adaptations to blasting, lighting, &c, — all 

 these had their origin in Faraday's discovery of voltaic induction. 



On the 20th of November, 1845, Faraday read to the Royal So- 

 ciety of London his startling discovery of the " Magnetization of 

 Light and the Illumination of Magnetic Lines of Force." This dis- 

 covery, from its delicacy and novelty, deserves to take rank as Fai-a- 

 day's greatest, standing, as Tyndall describes it, among his other dis- 

 coveries and overtopping them all like the " Weisshorn among moun- 

 tains, high, beautiful, and alone." 



It really means, however, less than the language in which it was 

 announced would convey to most minds. More than thirty years be- 

 fore, Seebeck and Brewster had succeeded in imparting to common 

 glass, by pressure or heat, the depolarizing structure of crystals. It 

 was reserved for Faraday to imitate, partially, the quartz-like structure 

 of oil of turpentine, and its strange power of circular polarization, by 

 subjecting his heavy glass, and even water, to the influence of strong 

 magnets. This discovery was followed by others, in rapid succession, 

 extending over a period of five years ; all of which are included in his 

 comprehensive classification of substances into Magnetics and Diamag- 

 netics. A compass needle made out of a diamagnetic would point 

 east and west, where an ordinary compass needle would point north 

 and south. As oxygen is powerfully magnetic, Faraday labored hard 

 to show that it was superfluous to seek for the cause of terrestrial mag- 

 netism, or at least of its fluctuations, outside of the earth's atmosphere. 

 The antagonistic properties of magnetism and diamagnetism are in- 

 fluenced by crystallization. Faraday proved this for bismuth, anti- 

 mony, and arsenic, as Plucker did for the optical axes of crystals. 

 Faraday could have had little expectation in 1825, when he was melt- 

 ing the borosilicate of lead, that this heavy glass, which proved a fail- 

 ure for optical purposes, on account of its deep color, would, after 

 standing on the shelf for thirty years, become the instrument of his 

 grandest discovery. 



