THE LEYDEX JAR. 625 



by the palm, and the three other fingers, the glass rod itself being 

 so directed with the right hand that it may glide during the rub- 

 bing constantly along the knob of the jar. The metal rod which 

 carries the knob should be a little bent if necessary to facilitate the 

 operation. 



The action of the Ley den jar is the same as that of 

 the condensing apparatus previously described. Elec- 

 tricity of some kind, usually positive, is communicated 

 to the inner coating, and effects electrical separation in 

 the outer coating, binding the opposite, usually negative, 

 electricity, and repelling the like, usually positive, elec- 

 tricity, which must be carried away, or it would exert a 

 repulsive action upon the electricity in the inner coating, 

 and would prevent its becoming bound, that is, con- 

 densation would be impossible. As ordinarily the jar 

 is held in the hand or placed upon the table, provision 

 is thus made for the outer coating being in conducting 

 communication with the ground. In order to prove that 

 the jar cannot be charged if the outer coating is insulated, 

 it is placed upon the cake of the electrophorus, or upon 

 a small insulating stool (if the electrophorus is in use), 

 which may be constructed by placing a disc of card- 

 board of the size of the bottom of the jar upon three 

 pieces of sealing-wax about 3 cm high. When the jar is 

 insulated, and electricity is communicated to the inner 

 coating, the free induced electricity in the outer coating 

 may be rendered manifest by placing the finger or 

 another conductor near it. If the jar is charged from 

 an electrophorus. sparks will be seen to pass, when the 

 distance between the coating and the conductor is not 



o 



more than 2 mm ; if it is charged from the machine the 

 distance may amount to 1 or l om> 5. 



When a charged jar is held in one hand, and a finger 



s s 



