58 ELEMENTARY LESSONS ON [CHAP. i. 



" shock " will be communicated to the muscles of the 

 wrists, elbows, and shoulders. A safer means of dis- 

 charging the jar is afforded by the discharging tongs 

 or discharger (Fig. 32), which consists of a jointed 

 brass rod provided with brass knobs and a glass handle. 

 One knob is laid against the outer coating, the other is 

 then brought near the knob of the jar, and a bright 

 snapping spark leaping from knob to knob announces 

 that the two accumulated charges have flowed together, 

 completing the discharge. 



52. Discovery of the Leyden Jar. The dis- 

 covery of the Leyden jar arose from the attempt of 

 Musschenbroek and his pupil Cuneus 1 to collect the 

 supposed electric " fluid " in a bottle half rilled with 



* ' water, which was held in the hand and was provided 

 with a nail to lead the " fluid " down through the cork 

 to the water from the electric machine. Here the 

 water served as an inner coating, and the hand as an 

 outer coating to the jar. Cuneus on touching the nail 

 received a shock. This accidental discovery created 

 the greatest excitement in Europe and America. 



53. Residual Charges. If a Leyden jar be 

 charged and discharged and then left for a little time to 

 itself, it will be found on again discharging that a small 

 second spark can be obtained. There is in fact a 

 residual charge which seems to have soaked into the 

 glass or been absorbed. The return of the residual 

 charge is hastened by tapping the jar. The amount of 

 the residual charge varies with the time that the jar has 

 been left charged ; it also depends on the kind of the glass 

 of which the jar is made. There is no residual charge 

 discoverable in an air-condenser after it has once been 

 discharged. 



54. Batteries of Leyden Jars. A large Leyden 

 jar will give a more powerful shock than a small one, 



1 The honour of the invention of the jar is also claimed for Kleist, 

 Bishop of Pomerania. 



