18 



ELECTRICAL MEASUREMENTS 



and 



D = 



(5) 



The value of D is to be made a maximum by properly choosing the 

 size of wire. In order that this may be done data must be at 

 hand concerning the resistance per unit volume of various sizes 

 of the insulated wire, as well as the relation of the thickness of 

 the insulation to the diameter of the conductor. In the pre- 

 liminary discussion of methods of measurement it is sufficient 

 to assume that G = K^/Ro, in which case the maximum deflection 

 is obtained when 



R = R 



that is, when the galvanometer resistance is equal to that of the 

 remainder of the circuit. If the galvanometer constant be 

 taken as 



G = K(R G ) n 



the deflection will be a maximum when 



(6) 



Some authorities recommend that n be taken as % instead of % 

 as just used. 



A table of rough data concerning a particular make of double 

 silk-covered wire is given below. 



TABLE OF ROUGH DATA ON D.S.C. Cu. WIRE 



