Electricity and Light. 455 



Plane of polarization at 45° to lines of force ; strong electric 

 action : the light comes out faintly, but very distinctly, from 

 extinction, and is then extinguished by compression of the com- 

 pensator parallel to the lines of force; vanishes abruptly at the 

 instant of discharge of prime conductor. 



38. Kerosene Oil. — This liquid is more purely transparent 

 than paraffin, but not such a strong insulator. When the plate 

 of liquid is specklessly clean, but not till then, the form of ex- 

 periment just described in the case of paraffin succeeds perfectly ; 

 and the effects obtained are similar, as might indeed be expected. 



Plane of polarization at 45° to lines of force ; strong electric 

 action : the light is restored faintly, but very clearly, from pure 

 extinction, and is then extinguished perfectly by compression of 

 the compensator parallel to the lines of force. As in all the 

 former cases, the restored light vanishes abruptly at the instant 

 of discharge of the prime conductor. 



Spirits of Turpentine. 



39. Two samples of this liquid, of contrary photogyric powers, 

 were mixed in such proportions as to give a plate inactive in the 

 polariscope. The plate was very transparent and a good insu- 

 lator. All the arrangements being as in the first and second 

 experiments on carbon disulphide, and the liquid being at last 

 quite clean, the action of the dielectrified turpentine in the po- 

 lariscope was found to be perfectly regular, similar to that of 

 benzol, but rather fainter, though not nearly so faint as the 

 actions of paraffin and kerosene. Even when some specks of 

 dirt were present, and formed an interterminal chain, there was 

 sometimes a good effect obtained above and below the chain. I 

 had occasion to notice particularly while working with this liquid, 

 what I had already observed more distinctly in the case of 

 paraffin, that it is sometimes of much consequence to receive the 

 most of the light through the centre of the electric field. 



Oil of Turpentine. — Plane of polarization at 45° to lines of 

 force; strong electric action: the light is restored, faintly but 

 very distinctly, from extinction, and is then extinguished by com- 

 pression of the compensator parallel to lines of force. Plane of 

 polarization at 0° or at 90° to lines of force, strong electric 

 action : no perceptible effect in the polariscope. 



Olive- Oil. 

 40. This liquid is, I believe, the best insulator among the 

 heavy oils ; and although coloured, it gives a beautifully trans- 

 parent plate. I have made a good many experiments upon it, 

 at several times, finding the material difficult to manage, and 

 trying to assure myself perfectly of the interesting fact that its 



