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



part was so small that I could not ascertain the fact decisively. 

 Two specimens of transparent fluor, lent me by Mr. Tennant, 

 gave the effect. 



2178. Rock-crystal, four inches across, gave no indications 

 of action on the ray, neither did smaller crystals, nor cubes 

 about three-fourths of an inch in the side, which were so cut 

 as to have two of their faces perpendicular to the axis of the 

 crystal (1692, 1693.), though they were examined in every 

 direction. 



2179. Iceland spar exhibited no signs of effect, either in 

 the form of rhomboids, or of cubes like those just described 

 (1695.). 



2180. Sulphate of baryta, sulphate of lime, and carbonate of 

 soda, were also without action on the light. 



2181. A piece of fine clear ice gave me no effect. I can- 

 not however say there is none, for the effect of water in the 

 same mass would be very small, and the irregularity of the 

 flattened surface from the fusion of the ice and flow of water, 

 made the observation very difficult. 



2182. With some degree of curiosity and hope, I put gold- 

 leaf into the magnetic lines, but could perceive no effect. 

 Considering the extremely small dimensions of the length of 

 the path of the polarized ray in it, any positive result was 

 hardly to be expected. 



2183. In experiments with liquids, a very good method of 

 observing the effect, is to inclose them in bottles from 1^ to 

 3 or 4 inches in diameter, placing these in succession between 

 the magnetic poles (2150.), and bringing the analysing eye- 

 piece so near to the bottle, that, by adjustment of the latter, 

 its cylindrical form may cause a diffuse but useful image of the 

 lamp-flame to be seen through it: the light of this image is 

 easily distinguished from that which passes by irregular re- 

 fraction through the striae and deformations of the glass, and 

 the phaenomena being looked for in this light are easily seen. 



2184. Water, alcohol, and aether, all show the effect; water 

 most, alcohol less, and aether the least. All the fixed oils 

 which I have tried, including almond, castor, olive, poppy, 

 linseed, sperm, elaine from hog's lard, and distilled resin oil, 

 produce it. The essential oils of turpentine, bitter almonds, 

 spike lavender, lavender, jessamine, cloves, and laurel, produce 

 it. Also naphtha of various kinds, melted spermaceti, fused 

 sulphur, chloride of sulphur, chloride of arsenic, and every 

 other liquid substance which I had at hand and could submit 

 in sufficient bulk to experiment. 



2185. Of aqueous solutions I tried 150 or more, including 

 the soluble acids, alkalies and salts, with sugar, gum, &c, the 



