500 ELECTRICITY. 



therefore, to discharge the jar it is necessary that a com- 

 munication should be formed between the inside and out- 

 side. This may be done by the hands of the experiment- 

 er. He grasps with one the external coating, and with 

 the other touches the knob, connected with the interior. 

 The communication is thus completely formed, and the 

 fluid will pass until the former equilibrium is restored. 



Nothing now is more common than for an individual 

 to approach a charged jar, standing upon a table, and to 

 touch its knob, without forming any communication with 

 the oittside. Now if the table is dry, it is a non-conduc- 

 tor, and of course though the fluid may pass down to 

 the floor, through the body of the experimenter, it can- 

 not rise through the table to the outside of the jar, except 

 in very small quantities. And the fluid will not leave 

 the inside, till it can, by this means, reach the outside. 

 The jar will consequently be but very slightly discharg- 

 ed. This mistake is made more frequently on account 

 of the fact, that, in order to discharge the prime conduc- 

 tor, nothing is necessary but to touch it with one hand. 

 For the opposite electricity is not, as in the Leyden jar, 

 situated in a small insulated plate, but is diffused among 

 all the surrounding bodies, as the floor, the ground, &c ; 

 and the feet of the operator naturally forms a communi- 

 cation with them. So that by simply touching the con- 

 ductor, a communication is actually formed, whereas 

 by touching the knob only of the jar it is not. 



For the purpose of discharging a Leyden jar, or a 

 combination of jars, called a battery, a very useful in- 

 strument is employed called a discharger. It consists 

 simply of two brass wires, united at one end by a hinge, 

 and having knobs on the other .extremities. The arms 

 may be opened to any distance, and from the hinge there 

 proceeds usually a glass handle. One of the knobs is 

 now brought into contact with the outside of the jar, and 

 the other with the inside, and the communication is at 

 once formed. 



Having thus shown what are the circumstances in 

 which a motion of the electric fluid takes place, we 

 proceed to explain the nature of this motion. 



jq--/i ft! );>RIW,- r*jf--tvrafi HMfcj 



