162 Dr. J. Kerr's Electro-optic 



amyl alcohol, gave now no sensible effect. The electro-optic 

 action was found to be purely negative, conspiring regularly 

 with compression parallel to lines of force, and giving no sen- 

 sible change (except an apparently instantaneous tremor of 

 the flame) with tension. 



Propyl alcohol («=3) shows an additional fall of power. 

 Tried with the Leyden jar, it gave a good restoration, though 

 not strong, with fifteen turns of the plate. Ten turns, powerful 

 with butyl alcohol, gave now no sensible restoration from ex- 

 tinction. The effect was purely negative, strengthened always 

 by compression parallel to lines of force, and not sensibly 

 affected by tension. 



Ethyl alcohol (n = 2), specific gravity "795, showed a large 

 fall of power. With plate machine and strongest charges of 

 the jar, it gave no sure trace of effect. With the large Ruhm- 

 korffs coil, working in the usual way with oscillating rheotorne, 

 it gave a strong heat-effect almost at once. The rheotome 

 was therefore worked by hand, separate discharges being 

 taken at intervals of 1 or 2 seconds. At each discharge, 

 there was a perfectly regular, but very faint, restoration from 

 pure extinction. Tested by the hand-compensator with great 

 care, the electro-optic action was found to be purely negative, 

 regularly neutralized or much weakened by tension parallel to 

 lines of force, and regularly strengthened by compression. 



Methyl alcohol (n=l), tried with strongest charges of the 

 jar, gave an effect which was clear and regular, but too feeble 

 to be characterized. Tried with separate discharges of the coil, 

 it gave a faint restoration regularly from pure extinction. 

 Tested by the hand-compensator with great care, the effect 

 was strengthened regularly by tension parallel to lines of force, 

 and neutralized or much weakened regularly by compression ; 

 so that this alcohol, contrarily to the preceding six, is distinctly 

 and purely positive. As far as I could judge, the action was 

 somewhat stronger than the contrary action of ethyl alcohol. 



Distilled icater (?i = 0), tried with strongest charges of the 

 jar, gave a clear effect, apparently better than that in methyl 

 alcohol, but still too faint to bo characterized. Tried with 

 separate discharges of the coil.it gave a faint restoration regu- 

 larly from pure extinction. The effect was found to be purely 

 positive, strengthened by tension parallel to lines of force, and 

 neutralized or much weakened regularly by compression. I 

 thought the action rather stronger than that of methyl alcohol, 

 and certainly not weaker. The experiment with one charge 

 of water could not be continued well for any length of time, 

 as the electro-optic field was obscured very soon by an ascend- 

 ing cloud of gases. 



