Chap, xi.] COMPENSATION OF CURRENT. 



121 







Com- 



A and B. On the wire is a slider s, which may be 

 moved from one end to the other, and makes contact 

 all the way. -It also carries a binding screw. This 

 simple rheocord is called the LOSTG COMPENSATOR. 

 From a constant element (E, Fig. 62) lead a wire to 

 A, and another to B. A key 

 may be interposed on the way. 

 From A and s wires are led to 

 the side cups of the commu- 

 tator which has the cross in, 

 and from end cups wires go to G, 

 the galvanometer. Now the 

 current from E will pass to 

 A, and may here branch into 

 two circuits, the long circuit A 

 by the commutator to G and back 

 through the commutator to s, 

 then on to B and back to E, and 

 the short circuit straight along " lg * 

 the wire AB and back to E. 

 Now, if the slider s is close up to A, it is easy to see 

 that all the current will be short>circuited, and none will 

 go through the galvanometer. If, however, the slider 

 is moved away from A, then a small amount of the 

 current will find its way through G, and this current 

 increases the farther s is removed from A. In fact, 

 the amount of current sent through G will be propor- 

 tional to the distance AS. Thus the strength of the 

 current sent through G can be varied at pleasure and 

 measured. Further, the current can be sent in either 

 direction through G by means of the commutator. If 

 the commutator be down towards 1, the current will 

 pass in the direction of the continuous arrow ; if the 

 commutator be down towards 2, the current will 

 traverse G in the direction of the dotted arrow. 



To carry out the scheme, the troughs are arranged in 

 the circuit of the galvanometer, as represented in Fig. 



