232 Dr. J. Kerr's Electro-optic 



39. Nut-oil. — In the first electro-optic trial this oil was very 



dirty: but it gave a good regular effect, which was neutralized 



• • • • 



(as the effect in olive-oil) by horizontal tension. After several 



nitrations and renewals of charge in the cell the oil was very 



little improved, still dirty and hazy, giving a faint diffused 



light even at initial extinction, and showing a heavy chain 



between the electrified balls, as well as dancing particles in the 



outer parts of the field. But amid the confusion thus produced 



the optical effect was obtained regularly and clearly. The 



effect was of the same kind as in olive-oil, but apparently 



stronger. 



40. Lard-oil. — As obtained from the oil-merchant this was 

 merely a thick slush ; but filtration gave a fine clear oil of a 

 bright amber colour. Tested in the usual way, it acted as a 

 pretty good insulator, the striking-distance of the prime con- 

 ductor being reduced by it about one half. As with nut-oil, 

 so here, I found that repeated nitrations and renewals of the 

 charge made little difference. The oil was never perfectly 

 clean : there were always a few flickering particles in the outer 

 parts of the field, as well as a stationary chain or set of chains 

 between the electrified balls. Still the effect of electric force 

 was observed regularly and very distinctly in the polariscope. 

 The effect was of the same kind (contrary to CS 2 ) as in olive- 

 oil, but certainly stronger. The extinction-bands, though not 

 in any case well developed, were brought out clearly by hori- 

 zontal tension of the hand compensator. 



41. Neatsfoot-oil, very like lard from first to last, but a 

 purer-looking oil, and clearly stronger as an insulator. Under 

 electric force it gave in the polariscope a perfectly regular 

 and very good effect, which appeared stronger than that of 

 lard. The effect was of the same kind as in all the preceding 

 oils, being neutralized perfectly by glass extended in a direc- 

 tion parallel to the lines of force. 



42. Sperm-oil. — Two samples were used, the purest that I 

 could obtain from the oil merchants. They differed a little in 

 colour, the one being a clear amber, and the other paler with 

 a tinge of green ; they differed also in insulating-power, the 

 striking-distance of the prime conductor being reduced fully 

 three fourths by one of them, and only about one half by the 

 other. Both samples were examined at some length and with 

 great care. Many successive charges were passed through 

 the cell, the last of them very clean; but even at the best the 

 liquid was somewhat hazy, as if from the presence of gelatinous 

 matter. One of the samples, the weaker insulator, gave no 

 sure trace of effect in the electro-optic experiment. The other 

 sample gave an effect which was undoubtedly real, but too 



