230 Dr. J. Kerr's Electro-optic 



transparent; and a very good insulator. As in all the insula- 

 ting liquids yet examined, so here, electric force restores the 

 light clearly from pure extinction in the polariscope. The 

 effect is a good deal stronger than some of those already ob- 

 served and certainly characterized. When a spark is drawn 

 from the prime conductor, the light restored by electric force 

 vanishes at once, though not with such apparently perfect 

 abruptness as in CS 2 . When the light is well and steadily 

 restored by electric action, and the hand compensator is ap- 

 plied in the usual way, horizontal compression is found to 

 strengthen the light in every case, while horizontal tension 

 weakens it to pure extinction. The action of olive-oil under 

 electric force is therefore contrary to that of CS 2 (9), the one 

 action being perfectly regular and (to sense) absolutely pure 

 as the other. 



33. Oil of Sweet Almonds, the best obtainable from the 

 apothecaries — paler, and apparently purer and finer than olive- 

 oil, and a very good insulator. The action of this liquid under 

 electric force in the cell is not distinguishable from that of 

 olive-oil, except that it appears rather stronger. Under good 

 conditions easily obtained, the neutralization of electric action 

 upon almond-oil by horizontal tension of glass is always per- 

 fect, 



. 34. Oil of Poppy-seed, got in a'good colour-shop as prepared 

 for the use of artists — colourless, transparent, and a good insu- 

 lator. I have never seen a perfectly clean charge of this oil 

 in the cell ; but I have obtained a regular effect with it in the 

 way already described (31). The action of the liquid under 

 electric force is similar to that of olive-oil, being always neu- 

 tralized perfectly by horizontal tension of glass. I thought 

 the effect somewhat fainter than those observed in the olive 

 and almond oils. 



35. Oil of Rape-seed. — As obtained from the oil-merchant, 

 this liquid contained a large quantity of sediment. After half 

 a dozen nitrations through Swedish paper, the oil was appa- 

 rently clean and very clear, and of a faint amber colour. It 

 acted in the cell as a moderately good insulator, the sparks 

 from the prime conductor being reduced in length about two 

 thirds when the connecting wires were put in position (10). 

 In electro-optic experiments with this oil I never got a per- 

 fectly clean charge of the cell ; but good optical effects were 

 obtained with perfect regularity above and below the centre of 

 the field. The effects were apparently a little fainter than 

 those just observed in poppy-oil : they were equally pure, and 

 of the same kind, the light restored by electric force from pure 

 extinction being strengthened always by horizontal compres- 



