ELECTRICITY. 346 



it to the knob of a coated jar. Repeat this oper- 

 ation for thirty or forty times, and the jar will 

 become charged. 



Cavallo mentions one of the above kind made 

 by him, with which he charged a coated phial 

 several times by once exciting, so strong as to 

 pierce a hole through a card at every discharge. 



When a glass is covered with sealing-wax, after 

 it is excited and laid with the waxed side down- 

 ward, and the glass uppermost, then on making the 

 usual experiment of putting the metal plate on it, 

 and taking the spark, &c. it will be attended with 

 contrary electricity to what it had before. 



The universal Discharger. 



This apparatus is of extensive use, and is com- 

 posed of the following parts: A is a flat board fif- 

 teen inches long, four inches broad, and one thick, 

 or thereabouts, which, forms the basis of the instru- 

 ment. B B (Fig. 6.) are two glass pillars, cemented 

 in two holes upon the board A, and furnished at 

 the top with brass caps, each of which has a 

 turning joint, and supports a spring tube, through 

 which the wires D D slide. Each of these caps is 

 composed of three pieces of brass, connected so 

 that the wires D D, besides their sliding through 

 the sockets, have two other motions, viz. an hori- 

 zontal and vertical one. Each of the wires D D is 

 furnished with an open ring at one end, and at the 

 other end having a brass ball, which, by a short 

 spring socket, is slipped upon its pointed extremity, 

 and may be removed from it at pleasure. E is a 

 strong circular piece of wood, five inches in di- 

 ameter, having on its surface a slip of ivory inlaid, 



