Electricity and Light. 457 



cially depended upou. In my last series of experiments upon 

 this liquid, I carried on the observations with unrelaxed care for 

 several days, till the effects came out with perfect regularity. 

 The action was found to be, as distinctly as possible, contrary to 

 that of carbon disulphide, and equal, or very nearly equal, 

 to that of benzol. I give here the final note which was taken 

 at the time of observation. 



Olive- Oil. — Plane of polarization at 45° to lines of force; strong 

 electric action : the light is restored very distinctly from extinc- 

 tion, and is then extinguished regularly and perfectly by tension 

 of the compensator parallel to the lines of force, and strengthened 

 always by compression in that direction. At 0°aud at 90° not 

 a trace of effect in the polariscope. 



Castor- Oil. 



41. The liquid plate is very clearly transparent, and acts as a 

 weak photogyre, separating the blue and red perceptibly in the 

 polariscope. This oil is not nearly such a good insulator as the 

 preceding, and has generally current-movements produced in it 

 by the electric action ; and accordingly the results of experiment 

 upon this liquid were very irregular and imperfect. The ar- 

 rangements were generally the same as in the first experiment 

 on bisulphide of carbon (29). 



Plane of polarization at 45° to lines of force : the light is re- 

 stored strongly from good extinction, and is then either pretty 

 well extinguished or greatly weakened by tension of the com- 

 pensator parallel to the lines of force, and strengthened always 

 by compression in that direction ; but in most cases the re- 

 stored light is wanting in delicacy of outline, general distinct- 

 ness, and steadiness — a clear proof that the molecular structure 

 of the oil is more or less roughly disordered by the electric 

 action. At 0° and at 90° the light is still restored by the elec- 

 tric action, and generally to almost as great intensity as in the 

 case of 45°. Judging from all the observations, I think that 

 the action of castor-oil is similar. to that of olive-oil. 



42. Summary. — Of the liquids examined, there are six which 

 have given definite and constant results, namely these — car- 

 bon disulphide, benzol, paraffin and kerosene oils, oil of turpen- 

 tine, olive-oil. These bodies are distinctly birefringent when 

 dielectrified, acting upon transmitted light as uniaxal crystals 

 with axes directed along the lines of force, the uniaxal being 

 negative in the case of olive-oil, positive in the other five cases. 

 Dielectrified olive-oil acts in the same way as dielectrified glass, 

 or as glass compressed along the lines of force ; the other five 

 liquids dielectrified act as resin dielectrified, or as glass extended 

 along the lines of force. Compared among themselves with 



