76 



ELEMENTS OF STATIC ELECTRICITY. 



light Spring, or a chain, which comes into contact with 

 the inside coating. 



Tin-foil is the usual coating, and is put on with paste, 

 covering both surfaces equally to within about three 

 inches of the top. Light sheet brass makes a more 

 substantial outside coating, and does not require at- 

 tachment to the surface. 

 It can also be used for 

 the inside coating, when 

 the mouth is the full 

 width of the jar and the 

 sides are straight. Sul- 

 phuric acid is also some- 

 times used for the inside 

 coating of jars designed 

 fur special purposes. 



An instrument called 

 a discharger is also repre- 

 sented at A, in Fig. 20. 

 It consists of a curved 

 brass rod, terminating 

 in balls, and having an 

 insulating handle, of 

 ebonite or glass, at- 



Fig. 20-Leyden Jar and Discharger. tached to its Center. It 



is sometimes jointed at the center, and furnished with 

 two handles, as represented at B, Fig. 20. Its use is the 

 same as that of the bent wire already described. 



The Leyden jar can be made of any insulating 

 material capable of being molded into the proper form; 

 but glass seems to be the only substance capable of 

 resisting the enormous strain to which the dielectric is 

 subjected under a full charge. 



