Non-conducting Bodies in Electric Induction. 13 



sulated globe induced, np the metallic insulated disc (edgeways 

 seen), so interposed that the line 

 joining the centres of the globes 

 passes perpendicularly through 

 the centre of the disc. According 

 to your view, the faces n and j) of the disc are more negative and 

 positive than when the disc was of atmospheric air (z. e. the metallic 

 disc away), and the induction on N must be stronger than before. 

 But really this is not always the case : the induction on N appears 

 strengthened or diminished, according as the intermediate metallic 

 disc is small or large, is thick or thin. I am not able to find by 

 your reasoning what difference should occur when the disc np 

 with the same diameter has a thickness of 025 or of 0'04! of an 

 inch. It seems to me, that in both cases the electric state of 

 the faces n and p should be greater than with the air-disc. How- 

 ever, with the thick metallic disc the induction on N appears 

 greater, with the thin disc less, than in the case where no disc 

 is present (p. 408 of my paper)*. When the thick disc is 

 employed, and therefore the induction on N appears strengthened, 

 if we touch the disc for a moment, and insulate it again, the in- 

 duction on N is diminished. If we say that the exalted state of 

 p is taken away by momentary touch, it is to be expected that 

 this state be fully restored at the moment when the disc is again 

 insulatedf. Be it as it may, I am not aware that your theory 

 admits the action of an inductric and an inducteous body upon 

 a third body to be independent of each other, and that is, I 

 beUeve, the essential point in which the two theories differ 

 thoroughly!. The old theory accounts in the simplest ima- 



* The induction of P is in my view not exclusively upon N, but upon 

 all surrounding boibes, even to the walls of the room. When the metallic 

 insulated disc np is changed in size, the distribution of the induction is 

 changed with it. A small plate, because of its thickness of conducting 

 matter, lessens the electric resistance between P and N, and the induction 

 on the latter is increased. A larger plate of the same thickness, or even 

 thicker, may diminish the induction on N by a redistribution of the forces ; 

 more induction upon surrounding bodies now takiug place, because of the 

 extension of its periphery towards them. — M. F. 



t I do not expect any restoration of the previous state of the disc, and 

 believe I know that it will not occur. A momentary uninsulating touch 

 instantly brings on a new state of the induction and of the plate, which is 

 final and remains after the uninsulating contact is removed. The only 

 disturbance of this state is that due to the presence of the uninsulating wire 

 which, whilst it is there, takes part of the induction on to itself, and that 

 caused by gradual discharge due to moisture and dust of the air aud to 

 imperfect insulation. — M. F. 



X The question to my mind is. Is the effect in the shell-lac plate np de- 

 pendent or independent of internal conduction amongst its particles? if 

 independent of internal conduction, what is it dependent on, apart from the 



