Observations on various Liquids, 233 



faint to be characterized in the usual way. I therefore applied 

 a more delicate method, which I have sometimes found very 

 useful. Working from the best possible extinction, and before 

 the electric force was applied, I introduced the hand compen- 

 sator, and applied a very feeble strain steadily, so as to merely 

 destroy the purity of initial extinction in one direction or the 

 contrary. The electric force was then applied; and I found re- 

 gularly that the effect of horizontal tension was clearly strength- 

 ened by electric force, and the effect of horizontal compression 

 clearly weakened. These results were obtained consistently 

 many times in succession, and with several successive charges; 

 but, considering their singularity, I could not be satisfied till 

 I had seen them under better conditions. 



43. Purified Sperm. — Sufficient quantities of the two pre- 

 ceding samples were given to Mr. Tatlock, the public analyst 

 for Glasgow; and he kindly had them purified for me with 

 great care, by a process which is described in Miller's i Che- 

 mistry.' As the oils left the hands of Mr. Tatlock he consi- 

 dered them extremely pure and dry. In electro-optic experi- 

 ment there was now no difficulty or doubt about either sample, 

 the effects being much stronger than before. By electric force 

 the light was well restored from pure extinction; and the effect 

 was always neutralized perfectly by horizontal compression of 

 glass, and always strengthened by horizontal tension. Judging 

 from memory, I thought the effect was at least as strong as 

 the similar effect observed in Young's light paraffin (29), and 

 a great deal stronger than the contrary effect observed in lin- 

 seed-oil (38). One thing is certain, that the action of sperm- 

 oil under electric force is of the same kind as that of carbon 

 disulphide, and contrary in character to the action of every 

 other fixed oil yet examined. 



44. Seal-oil, a transparent but somewhat hazy liquid, of a 

 pale amber colour, and a good insulator. In electro-optic ex- 

 periment this oil acted as regularly as the others already men- 

 tioned, and gave excellent effects, though it was never perfectly 

 clean. By electric force the light was restored brightly from 

 extinction in the polariscope, and the effect was neutralized 

 perfectly (as in olive-oil) by horizontal tension of the hand 

 compensator. The extinction-bands were developed clearly, 

 though not very strongly. The effects appeared to be the most 

 intense that I had yet seen in the fixed oils excepting colza. 



45. Codliver-oil, finest Norwegian, transparent, and of a 

 faint greenish colour. In electro-optic experiment this oil 

 gave regular and strong effects, which were neutralized per- 

 fectly (as in olive-oil) by tension of glass in a direction parallel 

 to the lines of force. The extinction-bands also were seen 

 dimlv. 



