NATURAL PHILOSOPHY. 127 



due to an electrical tension within the mass, sustained while the act of in- 

 duction continues, is evident by this, that if the carrier be applied t\vo or 

 three times alternately to the two faces, so as to discharge in part the elec- 

 tricity they show under the induction, then, on removing; the sulphur from 

 the induction field, it returns, not merely to neutrality or indifference, but the 

 surfaces assume the opposite states to what they had before, a necessary 

 consequence of the return of the mass of inner particles to or towards their 

 original condition. The same result may be obtained, though not so per- 

 fectly, without the use of any coatings. Having the uncoated sulphur in its 

 place, put the small spirit-lamp on the side way from the negative inductric ; 

 bring the latter up to its place, remove the spirit-lamp flame, and then the 

 inductric body, and finally, examine the sulphur; the surface towards the 

 flame, and that only, will be charged. Its state will be found to be positive, 

 just like the same side of the gilt sulphur, which had been touched two or 

 three times by the carrier. During the induction, the mass of the sulphur 

 had been polarized; the anterior face had become positive, the posterior had 

 become negative; the flame had discharged the negative state of the latter; 

 and then, on relieving the sulphur from the induction, the return of the 

 polarity to the normal condition had also returned the anterior face to its 

 proper and unchanged state, but had caused the other, which had been dis- 

 charged of its temporary negative state whilst under induction, now to 

 assume the positive condition. It would be of no use trying the flame on 

 the other side of the sulphur-plate, as then its action would be to discharge 

 the dominant body, and destroy the induction altogether. "When several 

 plates were placed in the inductive field, apart from each other, subject to 

 one common act of induction, and examined in the same manner, each was 

 found to have the same state as the single plate described. It is well known 

 that if several metallic plates were hung up in like manner, the same results 

 would be obtained. 



From these and such experiments, the speaker took occasion to support 

 that view of induction which he put forth twenty years ago (Phil. Trans., 

 1837), Avhich consists in viewing insulators as aggregates of particles, each 

 of which conducts within itself, but does not conduct to its neighbors, and 

 induction as the polarization of all those parties concerned in the electric 

 relation of the inductric and inducteous surfaces, and stated that, as yet, he 

 had not found any facts opposed to that vieAv. He referred to specific induc- 

 tive capacity, now so singularly confirmed by researches into the action of 

 submarine electro-telegraphic cables, as confirming these views; and also to 

 the analogy of the tourmaline, while rising and falling in temperature, to a 

 bar of solid insulating matter, passing in and out of the inductive state. 

 To the above report Prof. Faraday has since made the following addition : 

 The inquiries made by some who wish to understand the real force of the 

 test experiments relating to static induction, and their consequences in rela- 

 tion to the theory of induction, make me aware that it is necessary to men- 

 tion certain precautions which I concluded would occur to all interested in 

 the matter; I hope the notice I propose to give here will be sufficient. When 

 metallic coatings or carriers are employed for the purpose of obtaining a 

 knowledge of the state of a layer of insulating particles, as tho^e forming 

 the surface of a plate of sulphur, it is very necessary that they should exist 

 in a plane perpendicular to the lines of the inductive force, and in a field of 

 action where the lines of force are sensibly equal. Hence the importance of 

 adhering to certain fixed dimensions in the construction of the appar.iiu-, , 



