474 Professor Faraday on Static Induction. [Feb. \2, 



come into conductio?i contact with the surface particles of a mass of 

 insulating matter, and can take up the state of that surface, it is 

 only by real contact that this can be done. Therefore the two 

 sides of a block of sulphur were gilt by the application of gold 

 leaf on a thin layer of varnish, and when the varnish was quite dry 

 and hard this block was experimented with. Being introduced into 

 the induction field for a time and then brought away, it was found 

 free from charge on both its surfaces ; being again introduced, and 

 the carrier placed between it and either the gutta-percha or the 

 copper-plate, but not touching these or the sulphur, the carrier 

 when brought away showed no trace of electricity. The carrier 

 being again introduced at the inductive or gutta-percha side, made 

 to touch the gilt surface of the sulphur on that side, separated a 

 little way and then brought out to be examined, gave a positive 

 charge to the electrometer : when it was taken to the other side of 

 the sulphur and applied in the same manner, it brought away a 

 negative charge. Thus showing, that whilst the sulphur was under 

 induction, the side of it towards the negative gutta-percha was in 

 the positive state, and the side towards the positive inducteous 

 surface of copper bounding the extent of the induction field, was 

 in the negative state. Thus the dielectric sulphur whilst under 

 induction is in a constrained polar electrical state, from which it 

 instantly falls into an indifferent or natural condition the moment 

 the induction ceases, either by the removal of the sulphur or the 

 gutta-percha. That this return action is due to an electrical tension 

 within the mass, sustained while the act of induction continues, is 

 evident by this, that if the carrier be applied two or three times 

 alternately to the two faces, so as to discharge in part the electricity 

 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 perfectly, with- 

 out the use of any coatings. Having the uncoated sulphur in its 

 place, put the small spirit lamp between it and the copper-plate ; 

 bring up the excited gutta-percha to its place, remove the spirit- 

 lamp flame, and then the gutta-percha, 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 pos- 

 terior 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 discharged of its tern- 



