576 THE ELECTROPHORUS. 



which the disc may be raised from the cake. The cake 

 is electrified by briskly flapping it in an oblique direc- 

 tion with a piece of fur, for example, a cat- skin or a 

 fox-tail. If the cover is now placed upon the excited 

 cake and touched with the finger, a small spark passes 

 between disc and finger. If next the cover be raised 

 by the silk threads, it is strongly electrified, and if a 

 conductor be brought near it a smart spark passes. 

 When the cover is afterwards replaced upon the cake, 

 touched, and again raised, it is found to be again 

 charged, and the whole may be repeated many times 

 without electrifying the cake again. 



The electrical state of every part of the electrophorus 

 may be investigated by means of the ' carrier ' or c proof- 

 plane,' a small piece of metal attached to the end of a 

 slender rod of some non-conducting substance. If the 

 rod is held by the hand and the conductor at the end 

 of it applied to an electrified body, a small quantity of 

 electricity is communicated to the proof-plane and the 

 latter may be brought near to an electroscope instead 

 of the electrified body itself. 



Let the cake be briskly flapped, and the excited sur- 

 face be held over an electroscope which is charged with 

 electricity of a known kind, the motion of the gold 

 leaves will indicate that the cake is negatively charged. 

 The cake is now replaced upon the form and flapped 

 again, in order to make up for the loss of electricity 

 which happened during the first experiment, and the 

 metal disc placed upon it, taking care to hold it by the 

 strings and not to touch it. When the disc is again 

 lifted by the strings and brought near to an electroscope, 

 no electrical indication is observed, which proves that 



