98 Dr. J. Kerr's Electro-optic 



air was left in the top of the cell, it was drawn downwards by 

 the commotion of the strongly electrified liquid, and was 

 broken up into many small bubbles, which danced rapidly 

 through the field, and prevented all regular optical effect. 



The impression conveyed by the phenomenon in the case of 

 CS 2 was that of a simply statical arrangement of the dielectric, 

 a concatenation of electrically polarized particles of the liquid 

 along the curved lines of force, the electric action being in- 

 tense enough to overpower, so for, the gravitation of the par- 

 ticles. In the case of cumol the impression was different ; 

 the hump may have been produced, at least in part, by the 

 strong convection-currents which always accompanied it. Not 

 that there is any real inconsistency between these views ; for 

 there may evidently be a regular file-arrangement of particles, 

 kept up continually, or, rather, incessantly renewed, along the 

 curved lines of force, while there are gross currents of liquid 

 passing incessantly between the balls. 



24. Nitrobenzol (C 6 H 5 N0 2 ), new electvo-optic action. — This 

 oily liquid, though yellowish in colour, is very purely trans- 

 parent. Tested in the usual way, it acts as a good conductor 

 (10). When the two connecting-wires are in position, and 

 the machine is worked vigorously, no sensible spark can be 

 drawn from the prime conductor, no movement can be de- 

 dected in the liquid, nor any trace of the hump (23). And, 

 accordingly, in the electro-optic experiment arranged and con- 

 ducted as for CS 2 (8), nitrobenzol gives no trace of optical 

 effect, the extinction in the polariscope being as pure when 

 the machine is worked at the hardest rate as when it is at rest. 

 But it requires only a small change of the conditions to give 

 a large effect. 



The first connecting-wire, that from prime conductor to cell, 

 being kept always in position, the earth-wire is detached from 

 the second outer ball of the cell, and the observer at the polari- 

 scope brings up his knuckle slowly towards the latter ball till 

 a spark passes, the longer and denser the better. At the in- 

 stant of the spark (that is, at the instant of abrupt discharge 

 of the prime conductor through the liquid) there is a strong 

 restoration from extinction in the polariscope, not a mere 

 spark, nor a vague illumination, but a true restoration of the 

 old object, bright and clear and well outlined, as in many of 

 the former observations, though apparently instantaneous as 

 the spark itself. 



As the knuckle is brought up slowly to contact with the 

 ball, the restorations in the polariscope succeed each other 

 more rapidly, and become individually fainter. The light is 

 by-and-by sustained continually, but never without a sen- 



