Non-conducting Bodies in Electric Induction. 11 



which the mind conceives without difficulty, and leaves to mathe- 

 matics the pains to sura up the single eifects and to give the 

 amount of the sum. If theii' summation is often too complicate 

 to be completely eifectedj I think that not a fault of the theory, 

 especially as it is in most cases not difficult to imagine, by means 

 of general considerations, the final result. Therefore I have 

 long ago defended this theory against its — indeed not very dan- 

 gerous — antagonists, and I could not abstain from continuing 

 the defence, when an adversary arose in the man whom I vene- 

 rate as the greatest natural philosopher of the age. 



Upon your first remark I reply, that, writing on a case of in- 

 duction in air, I gave your opinion on that induction, and avoided 

 intentionally to mention your opinion on a case which had not 

 occurred; for had I mentioned it, I would have been forced to 

 add, that you admit solely a limited action at a distance*, and 

 to explain, that this presumption in respect to the case in hand 

 is of the same consequence as if you denied that action altogether. 



In respect of the reproof made in the second remark, that I 

 have misrepresented your meaning on the action of the conduct- 

 ing intermediate plates in induction, I must be the more anxious 

 to disculpate myself, as, if I am not mistaken, this disculpation 

 hits the very root of all differences between your theory of induc- 

 tion and the old one. I have said, it follows from your experi- 

 ments that the introduction of a conducting plate between an 

 inductric and an inducteous body would have diminished the 

 action of the former upon the latter, because this action, accord- 

 ing to your opinion, would pass in curved lines instead of in right 

 lines through the air. In the experiments referred to, a rubbed 

 shell-lac cylinder, and in contact with it an uninsulated metallic 

 disc, had been employed, and a fact of proof is given (Exp. Res. 

 1221), "that the induction of the shell-lac acts not through or 

 across the metal." This fact of proof consists in the observa- 

 tion, that a carrier ball receives inducteously no charge, or a 

 weak one, if it is applied to the centre of the upper face of the 

 disc, where the carrier is nearest to the inductric, and no straight 

 line can be drawn between both except through the metal ; and 

 the observation that the carrier receives a strong charge in the 

 air at some height above the centre of the disc. Hence you 

 conclude "that the inductionf is not through the metal, but 

 through the surrounding air in curved lines." I thought myself 

 entitled to presume that you would make the same conclusion 

 from the same fact of proof in experiments of a varied form, and 



* My view puts no limit to the action which is not paralleled in the case 

 of lipht ; where matter is, it is iueluded in the action ; where it is not, the 

 action is considered as J^oing on without it. — M. F. 



t On the fui'ther side, the metal being always uninsulated. — M. F. 



