304 THE ELECTRIC TELEGRAPH. 



element E has to pass through a resistance, r 1 , and through 

 the parallel circuit g (galvanometer) 

 and R (shunt). The whole resistance 



* R s 



, ,, , &g 



The intensity, I, of the current in r is 

 the sum of the intensity i in the shunt, 

 and that indicated by the deflection 

 a . Let the latter intensity be F (a), then 



and the current F (o) in the galvanometer is 



Now, with a given value of E, p, and <?, to make 

 _ E _ = 1 

 r' + r") (R + g) + K y 1,000,000 



we must put 



.y (/ + r"} ( 



1,000,000 r '(g + 9") ' 



It is sometimes convenient to make 



-| + 1 - 100 

 by which 



R= ^_ 

 99 



or the intensity of the current in the galvanometer branch 

 has to be multiplied by 100 to give the current in the main 

 circuit, and with this value inserted in the above formula, 

 the resistance, r, becomes 



.;.:, r'= 10,000 _(, +__) 

 of which r" and - may often be neglected. 



