504 ELECTRICItV. 



The former are called conductors, the latter non-conduc- 

 tors. For example, let a man grasp the outside of the 

 Leyden jar with one hand, and with the other touch the 

 knob with a piece of wood, and only a small portion of 

 the electricity will pass. Let him a moment afterwards 

 touch it with a piece of metal, and he will receive a vio- 

 lent shock. The whole force of the charge will pass 

 suddenly through the metal into his hand. 



It is easy to determine whether any substance is or is 

 not a conductor. If it contains anything metallic or 

 moist, it is, if not, it is a non-conductor. This is a gen- 

 eral, but not a universal rule. Silk and glass are the 

 most commonly used as non-conductors, and brass or 

 iron as conductors. 



The tendency of electricity to choose, as it were, the 

 best conductors may be shown by a variety of experi- 

 ments. Charge a Leyden jar, and bring into contact 

 with the outside of it, a wire, and a rod of wood. Let 

 the wire pass around the whole room, and the other ex- 

 tremity be brought near the knob. Let the other end of 

 wood also be brought to the same distance from the 

 knob, and then bring the two ends nearer and nearer 

 until the fluid darts across. It will invariably strike the 

 wire, although it must, by so doing, pass entirely round 

 the room, to reach its destination. 



In the same manner, if a variety of objects are laia 

 upon a table, such as chains, money, pieces of glass, &c. 

 Some of whom are conductors and some non-conductors, 

 and if they are placed almost in contact with each 

 other, and so arranged that there is one way, however 

 crooked, by which the electricity may pass across the 

 table through conductors only, except the very short 

 interruptions between them, the fluid will ^be sure to 

 find this way. If one end of the table is connected with 

 the inside, and the other with the outside, the fluid 

 will pass across, choosing with undeviating certainty the 

 conductors, and those alone. 



It is so with lightning. It darts from the cloud to the 

 earth, choosing the best conductors in its way. If a per- 

 son stands in such a manner as to be one of such a se- 

 ries of conductors the lightning will pass through him, 



