SCIENCE AND PRACTICE. 319 



ance, the shunt being changed to s 1 till the needle is again 

 deflected degrees, while H and g remain unaltered. 



The e f |ual intensities in the galvanometer circuits are 



and 



( + O (i + -f) + g 



from which 



E' = E 



A large battery, E 1 , being compared with a small one, E, 

 the shunt is only used in the case of the large one, and s 

 = oo may be inserted in the above formula, by which 



p. 



60. Professor Wheatstone's method is as follows : he 

 connects the element, E, to be measured, in circuit with a 

 galvanometer, while the whole resistance of the circuit is R. 

 The resulting deflection is 0. He then adds r units to 

 the circuit until the deflection is reduced to 0^ These deflec- 

 tions being noted, he puts the constant element E x in the 

 place of E, adjusts the new resistance Rj of the circuit until 

 the needle is deflected degrees, and adds to this r units, 

 until this deflection falls to X degrees as before. 



From these observations he has four expressions 



F (*)=-|- F (0) =-J 



