Observations on various Liquids. 101 



lated, showing that the fine deposit was in course of agglo- 

 meration. Among other trials now made, the first Mcol was 

 turned through a right angle, the second Nicol was turned 

 into the position of best attainable extinction, and the electro- 

 optic observation was repeated. Nothing like a good extinc- 

 tion was obtained in this case ; but the effect of electric action 

 was still considerable ; and it was evidently and considerably 

 weakened by a rotation of the second Nicol through a small 

 angle, the direction of this rotation being contrary to that 

 obtained in the first case. Several other charges of the cell 

 were tried from the same bottle ; but they were all speckled 

 or gritty from the outset, and gave no distinct effect. As far 

 as I can judge from memory and from imperfect notes taken 

 at the time, I think that the optical action of electric force 

 thus manifested in stannic chloride is to diminish the acute 

 angle between the plane of polarization and the lines of force. 



Such is the best account that I can give of an observation 

 which was unavoidably hurried, confused, and unsatisfactory. 

 The experiment is not one that I should like to repeat in the 

 same form ; it puts the instruments quite out of working order, 

 and tends also to damage them permanently. 



28. Other Liquids tried, but without effect. — Of these I may 

 mention particularly chloride of sulphur, pentachloride of anti- 

 mony, trichloride of phosphorus, tetrachloride of carbon, sul- 

 phide of allyl. These all acted as conductors (10), and gave no 

 sensible effect in the polariscope under electric force (8). I 

 should except sulphide of allyl, which gave good, though very 

 faint, traces of the nitrobenzol effect (24). I have little doubt 

 that the failure of most of the perchlorides was due to traces of 

 water, for which these compounds have an intense attraction. 



All the liquids mentioned up to this point were obtained as 

 pure chemicals from the establishment of Burbidge and 

 Farries. 



Organic L\ 



29. Young 's Paraffin Oil. — Specific gravity *814, a trade 

 sample of an illuminant, one of the lightest made, clear as 

 water, and. an excellent insulator. In the electro-optic expe- 

 riment, as for CS 2 , this liquid gives a very fine, but faint 

 effect : the light is well restored by electric force from pure 

 extinction ; and the effect is neutralized perfectly by horizontal 

 compression of glass. In intensity and range of effect, this 

 paraffin stands between amylene and terebene, but a good deal 

 nearer the latter. An illuminating paraffin was tried long 

 ago in the old plate cell, and with like effects, though much 

 fainter. 



Phil. Mag. S. 5. Yol. 8. No. 47. Aug. 1879. I 



