244 



Dr. J. Kerr's Electro-optic 



rating lines. The negative liquids are not so arranged ; but 

 colza and seal oils are certainly among the strongest, and 

 linseed is the weakest. 



Positive Liquids. 

 Carbon disulphide. 



Cumol. 



Paraffin-oil (sp. gr. -890). 



Carbon dichloride. 



Xylol. 



Toluol. 



Cymol. 



Benzol. 



Amylene. 



Paraffin-oil (sp. gr. •814). 



Sperm-oil. 



Terebene. 



Bromtoluol. 



Negative Liquids. 

 Fixed oils of vegetable origin: — 



Colza, 



Sweet almonds, 



Olive, 



Poppy-seed, 



Rape-seed, 



Nut, 



Mustard-seed, 



Linseed. 

 Fixed oils of animal origin : — 



Seal, 



Codliver, 



Lard, 



Neatsfoot. 



Valeric acid ? 



The birefringent actions of these twenty-six dielectrics 

 have been observed repeatedly ; they are perfectly regular, 

 and, to sense, perfectly pure. Valeric acid alone is so faint as 

 to be doubtful. 



(5) All the negative liquids yet known belong to the class 

 of the fixed oils. Sperm-oil holds an exceptional place, being 

 clearly positive. 



(6) The influence of density on electro-optic power is 

 marked and certain in the case of the paraffin oils, increase of 

 density being accompanied by increase of electro-optic power. 



(7) In carbon disulphide and several other liquids, electro- 

 optic measurements are manageable through long ranges of 

 potential and optical effect. The results of some careful 

 trials in this direction are given in 49 and 50. 



(8) Stannic chloride exerts a very strong optical action 

 under electrostatic force ; but the character of the effect is 

 not yet certainly known (27). 



(9) Of the forty or more liquids yet examined in the plate 

 cell, there are none that exhibit any moderate degree of 

 insulating power except the twenty-seven now named in 

 (4), (8). This appears to justify the generality of the state- 

 ment made in (1). 



