HISTORY AND PROGRESS. 157 



nected at each end with a metal style, which rests on a strip 

 of chemically prepared paper, supported on the under side 

 by a metal contact. The latter are connected to the -f. poles 

 of batteries E, the poles being to earth. Between the 

 metal styles and contacts are inserted resistances, and 

 secondary or compensating batteries, whose currents traverse 

 the paper strips in the reverse direction to those of the line 

 batteries, and prevent the decomposition of the salts con- 

 tained in the paper. 



Let the negative current of the line battery at station A 

 go from E to earth, and the positive current from E through 

 the metal supporting the paper strip, through the paper and 

 the style to the line a b, in the direction of the arrows ; at 

 station b it will go through the style, paper, contact rest, 



Fig. 86, 



and line battery, to earth; In traversing the paper at 

 station A, a decomposition of the salts would take place were 

 it not for the counteracting battery E', whose current, of 

 equal strength, passes from E' through w' t style, paper, &c., 

 preventing the chemical action, until a current, arriving 

 from b, or some such disturbance of the balance, causes an 

 appreciable difference of the currents enough to affect the 

 paper. 



The value of the resistance w, which is inserted in the 

 circuit of the counteracting battery to balance the currents, 

 may be calculated by the aid of Ohm's law, which will be 

 explained in the second part. 



Gintl subsequently employed a single key with five con- 

 tacts, instead of the double key just described. 



