97 
Preliminary experiments showed that the deflection pro- 
duced when the battery current was first sent through the 
electrolytic cell was not as great as it should be, owing to 
the time occupied in the coil moving to its deflected posi- 
tion, and to the great rapidity of the initial polarisation. 
It was finall}^ found that with the arrangement of the appa- 
ratus shown in the figure — 
B Battery. 
Kg Commutator. 
Ki and Ka Two way keys. 
G Galvanometer. 
S Shunt. 
R Large resistance (about 4,000 ohms). 
T Electrolytic cell. 
r Compensating Resistance = that of T, which was 
measured by Kohlrausch’s method.* 
the best results could be obtained by the following method : 
(a) Deflections were obtained indicating the strength of 
the current from B, when T was out of, r in, circuit. 
(h) The cell T was put in circuit, and scale readings taken 
every five seconds till the deflection became constant. If 
the reading (a) is proportional to E of battery, the final 
reading (fi) is proportional to E — e, where e is the back 
E.M.F. due to polarisation. 
(c) The battery B was switched out of circuit, and read- 
*■ Wiedemann’s, Annalen 11, p. 63 (1880). 
