Oh'the PhcenoTTienaofihe Electropfionis. 30 1 



When the cake is excited by friction, a change in its 

 capacity may be conceived to take place, and it acquires 

 through its whole substance a stronger attraction for the 

 electric fluid than it had before, and of course will become 

 disposed to receive an additional quantity. The sole is 

 placed on an insulated stand, which, when the cake is im- 

 posed, participates in the disposition to receive; and the 

 pith ball electrometer attached to it diverges with negative 

 Electricity. Eat it not only partakes of the character of the 

 cake ; the capacity of the sole thus in contact with the ex- 

 cited substance is augmented J and it does not merely operate 

 a-; a conductor to convey the fluid to the cake, but obtains 

 Jor itself, froni contiguous bodies floating in the atmosphere, 

 more than in its separate state it is capable of holding. Ou 

 the removal of the cake, therefore, carefullv avoiding to de- 

 stroy the insulation of the sole, the attractive force of the 

 ^')lc is diminished. It is left in a plus or positive state, is 

 -'iisjjosed to part with its superfluous quantity, and the balls 

 diverge with positive electricity. 



While the excited cake remains imposed, and the soie 

 electrometer indicates the negative eleelricitv, a conductor 

 i3 offered to the excited surface. Tlie attraction of the cake 

 becomes strongest on thp upper side, because any supply is 

 obtained with ntore facility by the op<n-iing of a communi- 

 cation with the universal store diffused in the ffround. The 

 fioie electrometer closes, therefore, on account of the dinii- 

 nished activity of force on the under surface ; and when the 

 communication is complete, bv the contact of the conduct- 

 ing substance, the sole acquires the same staic, i. e. po5;i- 

 tive, and for the same reasons as when the cake is removed. 

 On wliiidrAwmg the iiand, or other conductor, the former 

 state is restored. 



When the sole is not insulated it is diincu't, and fre- 

 quently impracticable, to ascertain its state of electricitv. 

 Hie co«?er inqjo^ed by its insulating handle appears by its 

 t'lectronu'ter to be slightly positive; and the sole, by its at- 

 traction for the pith balls attached to tlie cover, indicates a 

 neg-ative state. I am at a loss to explain this circumstance, 

 unless it be supposed that the force of attraction is ])rinci- 

 pally exerted downwards in consetpiL-nce of its uninterrupted 

 Cftunnuniea'tion Vv'ilh the ground: that the activity of the 

 upper surface is soon neutralized by the inqiosition of the 

 cover; and that the cover i> brought into the state of the 

 sole when iiisulited and the cover imposed, i. c. dive.riics 

 witli positive electricity; but \n eonsc"(pience of its increased 

 cajKicity, arising from its contact with the eycited electric, 

 7 it 



