VOLTAIC ELECTRICITY. 621 



these hypothetical currents being in non-conducting dianiagnetic, as in 

 magnetic bodies, not in the mass, but round the particles of the matter. 



Magneto-optic Effects and Magnecrystallic Polarity. 



Not even yet have we terminated the enumeration of the co-existent 

 polarities which in this province of nature have been brought into view. 

 Light has polar properties ; the very term polarization is the record of 

 the discovery of these. The forces which determine the crystalline 

 forms of bodies are of a polar nature : crystalline forms, when complete, 

 may be defined as those forms which have a certain degree of symme- 

 try in reference to opposite poles. Now has this optical and crystal- 

 line polarity any relation to the electrical polarity of which we have 

 been speaking ? 



However much we might be disposed beforehand to conjecture that 

 there is some relation between these two groups of polar properties, 

 yet in this as in the other parts of this history of discoveries respect- 

 ing polarities, no conjecture hits the nature of the relation, such as 

 experiment showed it to be. In November, 1846, Faraday announced 

 the discovery of what he then called " the action of magnets on light." 

 But this action was manifested, not on light directly, but on light pass- 

 ing through certain kinds of glass. 8 When this glass, subjected to the 

 action of the powerful magnets which he used, transmitted a ray of 

 light parallel to the line of magnetic force, an effect was produced 

 upon the light. But of what nature was this effect ? When light was 

 ordinary light, no change in its condition was discoverable. But if the 

 light were light polarized in any plane, the plane of polarization was 

 turned round through a cer.tain angle while the ray passed through the 

 glass : a greater angle, in proportion as the magnetic force was 

 greater, and the thickness of the glass greater. 



A power in some respects of this kind, namely, a power to rotate 

 the plane of polarization of a ray passing through them, is possessed 

 by some bodies in their natural state ; for instance, quartz crystals, and 

 oil of turpentine. But yet, as Dr. Faraday remarks," there is a great 

 difference in the two cases. When polarized rays pass through oil of 

 turpentine, in whatever direction they pass, they all of them have their 



8 Silicated borate of lead. See Researches, 2151, &c. Also flint glass, rock 

 alt, -water (2215). 



9 Researches, Art. 2231. 



