BRANCH CIRCUITS AND SHUNTS. 249 



balance shall have the same sensitiveness before and after the 

 passage of the current. The action is then a maximum. 



The current is transmitted to the movable coils by strips of thin 

 tinsel 5 mm", to 6 mm. in breadth. The resistance of these strips is 

 very small. Owing to their large surface they do not become appre- 

 ciably heated, and they dp not prevent oscillations. 



867. BRANCH CIRCUITS AND SHUNTS. When the intensity of 

 the current to be measured is too great for the sensitiveness of the 

 galvanometer, a given fraction of it is measured by a branch circuit. 

 The principal current, terminating at the two terminals of a gal- 

 vanometer, is divided into two parts, one of which passes through 

 the coil and the other by a branch circuit, to which is usually given 

 the name of shunt. 



If g is the resistance of the galvanometer, s that of the shunt, 

 I the principal current, * that which passes in the galvanometer with 

 the shunt, we have 



(33) */-*(I->^I r - or I-,\ 



g+s 

 The factor - = m, by which the current observed must be mul- 



tiplied to obtain the value of the principal current, is called the 

 multiplying power of the shunt. 



The resistance g^ of the system, formed by the shunt and the 

 galvanometer, is 



a- = = 



i i g + s m' 



g s s 



In order to have a shunt of power m it is better, instead of 



tr 



measuring the resistance s = - , to adjust the wire on the two 



m - i 



terminals of the galvanometer until the resistance of the whole is 



f 

 equal to . 



m 



Let us suppose that the circuit contains a constant electromotive 

 force E. Let R be the resistance external to the terminals of the 

 galvanometer, I the intensity which the current would have in the 



