296 Dr. Faraday's Researches in Electricity. [Series xix. 



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 trans- 

 parent 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. 



2151. Sixteen years ago I published certain experiments 

 made upon optical glass*, and described the formation and 

 general characters of one variety of heavy glass, which, from 

 its materials, was called silicated borate of lead. It was this 

 glass which first gave me the discovery of the relation between 

 light and magnetism, and it has power to illustrate it in a 

 degree beyond that of any other body ; for the sake of per- 

 spicuity 1 will first describe the phasnomena as presented by 

 this substance. 



2152. A piece of this glass, about two inches square and 

 0*5 of an inch thick, having flat and polished edges, was placed 

 as a diamagnetic (2149.) between the poles (not as yet mag- 

 netized by the electric current), so that the polarized ray 

 should pass through its length ; the glass acted as air, water, 

 or any other indifferent substance would do; anGjifSthe eye- 

 piece were previously turned into such a position that the 

 polarized ray was extinguished, or rather the imagflyproduced 

 by it rendered invisible, then the introduction of this glass 

 made no alteration in that respect. In this state of circum- 

 stances the force of the electro-magnet was developed, by 

 sending an electric current through its coils, and immedi- 

 ately the image of the lamp-flame became visible, and conti- 

 nued so as long as the arrangement continued magnetic. On 

 stopping the electric current, and so causing the magnetic 

 force to cease, the light instantly disappeared ; these phasno- 

 mena could be renewed at pleasure, at any instant of time, 

 and upon any occasion, showing a perfect dependence of 

 cause and effect. 



2153. The voltaic current which I used upon this occasion, 

 was that of five pair of Grove's construction, and the electro- 

 magnets were of such power that the poles would singly sus- 

 tain a weight of from twenty-eight to fifty-six, or more, pounds. 



* Philosophical Transactions, 1830, p. 1. I cannot resist the occasion 

 which is thus offered to me of mentioning the name of Mr. Anderson, who 

 came to me as an assistant in the glass experiments, and has remained ever 

 since in the Laboratory of the Royal Institution. He has assisted me in all 

 the researches into which I have entered since that time, and to his care, 

 steadiness, exactitude, and faithfulness in the performance of all that has 

 been committed to his charge, I am much indebted. — M. F. 



