A CCVMULA TORS. 1 1 



Glass suitable for the purpose must be free from any 

 substance which makes it a partial conductor. Hence 

 such glass as is commonly used for fruit jars, candy 

 jars, and druggist's bottles cannot be used, since it con- 

 tains metallic substances. 



Glass of a bright green color, free from bluish tint, 

 also the kind known as "hard flint," makes the best 

 Ley den jars 



The Leyden jar is charged by an electric machine ; 

 its inner coating being connected with the machine, 

 and its outer coating with the earth, or with the op- 

 posite electrode of the machine ; though it is not 

 material which coating is connected with the machine, 

 except as a matter of convenience. The jar may 

 be insulated, and the charge given to the outer 

 coating, if the inner coating is connected with the 

 earth. 



It is also immaterial whether the charge given is 

 positive or negative, as the opposite charge will always 

 be induced on the opposite surface ; electricity being 

 repelled to the earth when a positive charge is given, 

 or attracted from the earth when negative is given. 



The electromotive force (E. M. F.) of a jar is equal 

 to the difference of potential between its inner and 

 outer coatings. 



CHARGE BY CASCADE. The method of charge by 

 cascade, first proposed by Franklin, is as follows : Let 

 a number of jars of equal size, as A, B, C, Z>, be 

 arranged as represented in Fig. 21 ; the outer coating 

 of each, commencing with A^ being connected with the 

 inner coating of the one next to it ; D having its outer 

 coating connected with the earth, and A having its 

 inner coating connected with the machine. And let A, 



