410 Dr. C. V. Drysdale on the Use of the 



the case, with a throw-over switch, permitting the instrument 

 to be used as either a direct or alternate current potentio- 

 meter. 



Fio-. 4. 



Fig. 5 shows the connexions, which need little explanation. 

 The main circuit of the potentiometer, consisting of the 

 rheostats Rj and R 2 , the two dials D x and D 2 , the slide-wire 

 W, and the dynamometer D, is connected to two of the blocks 

 of the change-over switch C, which is similar in form to the 

 well-known selector switch used in the Crompton Potentio- 

 meter. The derived P.D. from the dial D 2 and slide-wire 

 contact is led by the key K and the selector switch S to tu o 

 more of the contacts on C. The remaining eight contacts on 

 C are connected in pairs to the phase-shifting transformer P, 

 the battery terminals D.C., the ordinary galvanometer 

 terminals Gr, and the vibration galvanometer terminals V.Gr. 

 The phase-shifter primary is excited from the terminals A.C., 

 which are here shown four in number, for two-phase or split- 

 phase. A single motion of the switch C to right or left 

 connects the main circuit of the potentiometer on to the 

 battery or secondary of the transformer, and simultaneously 

 connects the sliding contacts through the selector switch to 

 the appropriate galvanometer. The key K being provided 

 with a holding-down cam, leaves the hands free to move the 

 potentiometer contacts and rotate the phase-shifter simul- 

 taneously. A frequency meter F of the vibrating reed type 

 may be fixed on the base if desired, in which case the instru- 

 ment is available for inductance and capacity measurements. 



