Experiments on various Liquids. 253 



was more intense but not so pure, the liquid being much 

 disturbed. 



Benzoyl hydride, or oil of bitter almonds (C 7 H 5 0, H), is 

 positive, and a very weak insulator. Without the jar, it gave 

 a clear restoration, too abrupt for the hand-compensator. 

 With moderate charges of the jar, the effect was still extremely 

 quick but certainly positive, strengthened by tension, and not 

 affected by compression. 



Ethylene monacetate, C 4 H 8 3 , ranks with the other acetates 

 and the formates as very impurely positive. With weak dis- 

 charges of the jar, the effect was too faint to be characterized, 

 or even regularly seized ; and with strong discharges of the 

 coil, the liquid was very much disturbed. With moderate 

 charges the effect was to all appearance positive, but very 

 impure at the best. 



Methyl salicylate, or oil of wintergreen, C 8 H 8 3 , is purely 

 positive. As a conductor, without the jar, it gave a sensible 

 but very faint restoration. With strong charges of the jar, 

 the effect was pretty strong and certainly positive, the contrast 

 between tension and compression being clear and' regular, 

 though there was no weakening in any case by compression. 



The effect was examined afterwards more closely with the 

 Ruhmkorff-discharges, and with a special eye-piece described 

 in one of my former papers — an acute prism of glass, revolving 

 regularly round the line of vision, and exhibiting the progress 

 of the phenomenon in time as an extension in space. Viewed 

 in this way, the effect was strengthened by tension as formerly, 

 and was also extinguished regularly and perfectly by com- 

 pression. I have already referred to this form of experiment 

 as one that would afford a clear proof of the purity of positive 

 or negative character of a dielectric, in cases where the hand- 

 compensator gives a sensible increase of intensity when con- 

 spiring with the electric strain, but no sensible decrease when 

 opposing it. 



28. Beeswax is purely negative, as are also all the fused 

 fats that have been examined, with the exception of sperma- 

 ceti, which is strongly positive. 



Palm-oil, cacao-butter, lard, and talloiu were tried succes- 

 sively in the fusion-cell as examples of the fats. There was 

 generally a little disturbance by movements in the liquid; but 

 the optical effects were distinctly and regularly negative, 

 strengthened by compression, and neutralized by tension. 



Spermaceti was then tried in the same way, and was found 

 to be purely positive, like sperm-oil among the fixed oils ; but 

 it was much stronger than was expected, stronger indeed than 

 any of the negative fats. As a nonconductor, and with a half 



