418 Mr. Faraday's Researches in Electricity. {Series XI.) 



proved the growing necessity of a more close and rigid exa- 

 mination of the whole question. 



1267. The shell-lac was of the best quality, and had been 

 carefully selected and cleaned ; but as the action of any con- 

 ducting particles in it would tend, virtually, to diminish the 

 quantity or thickness of the dielectric used, and produce 

 effects as if the two inducing surfaces of the conductors in that 

 apparatus were nearer together than in the one with air only, 

 I prepared another shell-lac hemisphere, of which the material 

 had been dissolved in strong spirit of wine, the solution fil- 

 tered, and then carefully evaporated. This is not an easy 

 operation, for it is difficult to drive off the last portions of 

 alcohol without injuring the lac by the heat applied ; and 

 unless they be dissipated, the substance left conducts too well 

 to be used in these experiments. I prepared two hemispheres 

 this way, one of them unexceptionable; and with it I repeated 

 the former experiments with all precautions. The results 

 were exactly of the same kind ; the following expressions for 

 the capacity of the shell-lac apparatus, whether it were app. 

 i. or ii., being given directly by the experiments 1*46, 1'50, 

 1'52, 1'51 ; the average of these and several others being very 

 nearly 1*5. 



1268. As a final check upon the general conclusion, I then 

 actually brought the surfaces of the air apparatus, corre- 

 sponding to the place of the shell-lac in its apparatus, nearer 

 together, by putting a metallic lining into the lower hemi- 

 sphere of the one not containing the lac (1213.). The di- 

 stance of the metal surface from the carrier ball was in this 

 way diminished from 0*62 of an inch to 0'4f35 of an inch, 

 whilst the interval occupied by the lac in the other apparatus 

 remained 0*62 of an inch as before. Notwithstanding this 

 change, the lac apparatus showed its former superiority; and 

 whether it or the air apparatus was charged first, the capacity 

 of the lac apparatus to the air apparatus was by the experi- 

 mental results as 1*45 to 1. 



1269. From all the experiments I have made, and their 

 constant results, I cannot resist the conclusion that shell-lac 

 does exhibit a case of specijic inductive capacity. I have tried 

 to check the trials in every way, and if not remove, at least 

 estimate, every source of error. That the final result is not 

 due to common conduction is shown by the capability of the 

 apparatus to retain the communicated charge; that it is not 

 due to the conductive power of inclosed small particles, by 

 which they could acquire a polarized condition as conductors, 

 is shown by the effects of the shell-lac purified by alcohol ; 

 and, that it is not due to any influence of the charged state, 



