ELECTRICITY. 383 



Explain theae. '^^^ P^^^'P^'^ ^^ ^*^° ^^-''^'^ "^^^ ""^^ FW. 321. 



tion and con- be best explained by describing what 13 

 Btructionofthe cg,\\ei the "coated," or "fulminating 

 Coated Pane. „ „,, . .. , , -,.■ 



pane. This consists of a glass plate, b ig. 



321, a, having a square leaf of tin-foil, b, attached to each 



Bide. If the plate be laid upon a table, and a chain from 



the prime conductor of an electrical machine be brought 



in contact with the tin-foil upon one side, the plate will 



become charged — the upper side with positive, and the 



under with negative electricity. 



If two such conductors, as the plates of tin- foil attached to 



coated pane a pane of glass, be strongly charged with electricity in the 



produce an eiec- Q^anncr described, and then, by means of the human body, bo 

 tnc shock? . . ' ■' , • 



put in communication — which may be done by touching ono 



plate with the fingers of one hand, and the other with the fingers of the other 

 hand — the two electric fluids in rushing together, pass through the body, and 

 produce the phenomenon known as the electric shock. 



154. The Leyden Jar is constructed upon the same princi- 

 ncr '^was ™the E^® ^^ ^^^ coated pane, and its discovery, accompanied with 

 principle of the the first experience of the nervous commotion known as the 

 madt^known?''' electric shock, occurred in this way: In 1746, while somo 

 scientific gentlemen at Leyden, in Holland, were amusing them- 

 selves with electrical experiments, it occurred to one of them to charge a 

 tumbler of water with electricity, and learn by experiment whether it would 

 affect the taste. Accordingly, having fixed a metafile rod in the cork of a 

 bottle fiUed with water, he presented it to the electrical machine for the pur- 

 pose of electrifying the water, holding at the same time the bottle in his hand 

 by its external surface, without touching the metallic rod by which the elec- 

 tricity waa conducted to the water. The water, which is a conductor, re- 

 ceived and retained the electricity, since the glass, a non-conductor, by which 

 it was surrounded, prevented its escape. The presence of free electricity in 

 the water, however, induced an opposite electricity on the outside of the glass, 

 and when the operator attempted to remove the rod out of the bottle, he 

 brought the two electricities into communication by means of his hand, and 

 received, for the first time, a severe electric shock. ' Nothing could exceed 

 the astonishment and consternation of the operator at this unexpected sensa- 

 tion, and in describing it in a letter immediately afterward to the French 

 philosopher Reaumur, he declared that for the whole kingdom of France he 

 would not repeat the experiment. 



The experiment, however, was soon repeated in different parts of Europe, 

 and the apparatus by which it was produced received a more convenient 

 form, the water being replaced by some better conducting substances, aa 

 metal fiUngs, for which tin-foil was afterward substituted. 



The Leyden Jar, as usually constructed, con- 



constniction of sists of a glass jar, Fig. 322, having a wide 



<;y enjar. jj^^^^]^^ ^^^j^ coatod, cxtemally and internally, to 



