Experiments on various Liquids. 157 



temperature of the laboratory. The conditions of experiment 

 with the fusion-cell are always in some degree unfavourable ; 

 so that a moderately strong effect obtained with this instru- 

 ment may be accepted safely as an evidence of high electro- 

 optic power in the dielectric. This remark applies to several 

 important bodies (phosphorus, cetyl and cinnyl alcohols, sper- 

 maceti, &c), which have given good effects in the fusion-cell. 



Elementary Bodies. 



3. Bromine, phosphorus, and sulphur, all in the liquid state, 

 are found to be elecfro-optically active and purely positive. 



Bromine was examined in the plate cell without effect; but 

 this trial was indecisive, as the plate of liquid was almost 

 opaque to the sunbeam. I therefore had a special cell con- 

 structed, shaped like the fusion-cell, but only a quarter inch 

 thick. As inductive terminal I used the long conductor of 

 the fusion-cell, supported by its proper stand; the other con- 

 ductor was a rounded segment of a disk of brass, resting on the 

 floor of the cell, and connected by a lateral wire to earth. All 

 the metallic pieces were plated with platinum; and the fumes 

 from the liquid were sufficiently confined by a covering of soft 

 leather pressed lightly on the mouth of the cell. The optical 

 conditions were now very favourable. The image of the sun 

 in the mirror of a porte-lumi&re, viewed through the centre of 

 the electric field, was of course deeply coloured and much 

 weakened; but it still presented a fine object in the polariscope : 

 the extinction also was pure and sharp ; and the object was 

 well restored by a very feeble strain of the hand-compensator. 



Tried as a nonconductor, the plate of bromine gave no 

 optical effect; nor did it give any sensible spark in the test for 

 insulation. Tried then as a conductor, with moderate charges 

 of the jar, it gave a regular and very fine restoration, vivid 

 and undistorted, and not at all abrupt. When tested by the 

 hand-compensator, the effect was found to be purely positive, 

 strengthened by tension parallel to the lines of force, and 

 weakened to extinction by compression. 



Phosphorus was examined in the fusion-cell, at a tempera- 

 ture a little above its melting-point. Several trials were made 

 before a sufficiently clean plate was obtained; but I succeeded 

 at last, by pressing out the phosphorus through a bag of 

 chamois-leather, under hot water. The cell, charged nearly 

 full with phosphorus, and then filled up with water, was placed 

 in the hot-air bath, between the two Nicols ; and the experi- 

 ment was carried forward as in the case of bromine. The con- 

 ditions of optical observation were unfavourable, the cell-panes 

 being strongly and not very regularly strained by the heat. 



