1846] WRITINGS OF JOSEPH HENRY. 243 



EXPERIMENT ON THE MAGNETIC POLARIZATION OF LIGHT. 



(Proceedings of American Philosopliical Society, vol. iv. pp. 229, 230.) 

 January 16, 1846. 



Dr. Patterson read a portion of a letter from Professor 

 Henry in which he describes the manner in which he had 

 repeated the experiment of Mr. Faraday on tlie magnetic 

 polarization of light. 



" - - - This consists in producing in pure water and 

 other liquids a new arrangement of particles by which they 

 become possessed of the property of circular polarization dur- 

 ing the time a current of galvanism is circulating around them. 

 The arrangement I employed was as follows: A tube of glass 

 was filled with pure water and the ends closed with plates of 

 glass; this was placed in the axis of an iron tube, and this 

 again inserted into the axis of a coil consisting of about eight 

 hundred feet of copper wire. The ends of the iron tube were 

 closed with corks, through one of which was passed a Nicol's 

 prism, and in the axis of the other was fastened a plate of 

 tourmaline. This tube being directed to the clear sky, and 

 the tourmaline, which was placed next the eye, so turned that 

 it presented a dark field of view, a current of galvanism from 

 twenty-two cups of a Daniell's battery was passed through the 

 coil. At the moment of making the communication with 

 the battery the field became light, and when the circuit was 

 broken it again appeared dark. A slight rotation of the 

 tourmaline also produced darkness while the galvanic cur- 

 rent was passing, which indicated a twist in the plane of 

 polarization of the prolonged beam. The same effect was 

 produced without the iron tube but not to the same extent." 



