ELECTRO-CHEMTCAL EQUIVALENT OF SILVER. 
423 
at C between the brass coil of the dynamometer D and the ebonite coil E. The 
remaining terminals of these coils are led into mercury cups F and H, into which also 
dip the terminals of the bridge galvanometer g. With the ebonite coil is associated 
a resistance box N. The other branches of the balance were (in one arrangement) 
composed of a coil of 10 units in multiple arc with which was placed a high resistance 
box K, and three coils combined in series whose values were about 24, 1 , 1 units, making 
together 26. All these coils were of the standard pattern, and their values had been 
already carefully determined. From the cup L the current passed back to the key B. 
The high resistance box K gives a line adjustment by which the ratio of resistances 
can be brought to the required value. The smallest resistance actually used here was 
4000 units. While the electromagnetic balance was under observation a horse-shoe 
piece of stout copper rod P, connected with the key as shown in the figure, was inserted 
in the cups F, H. By this means these cups are brought accurately to the same 
potential, and nearly all the current is diverted from the standard resistance coils. 
The determination of the electromagnetic balance is rendered more troublesome by 
the fact that the first motion of the magnet on the reversal of the current is influenced 
by induction, and cannot be used as a test. No attempt was made actually to com¬ 
plete the adjustment, but by preliminary trials resistances from N differing by about 
yq unit were found, such that the effects observed were reversed in passing from one 
to the other. From the magnitude of these effects the required result is obtained by 
interpolation. At the beginning and end of a series the two ratios of resistances were 
determined by use of K, the horse-shoe P being of course withdrawn; and the mean 
of the initial and final values (which usually differed extremely little) was employed 
in the reduction. 
As an example, we may take some observations on Sept. 5, 1883, with the coil of 
the dynamometer marked B. The difference of readings on reversal of the battery in 
a given manner was taken alternately with certain resistances from N, which we may 
call a and b. The results were 
with a -j- ‘7, + ’3, +1*3, +I'0 mean + '8 ; 
with b —8'4, —8'4, —8'5, —9‘5 mean —8’7. 
Now with a the resistance from K, associated with the [10], and necessary for the 
resistance balance, had to be such that (at a standard temperature) the resultant 
resistance of this branch was 9*97772 ; while with b the resultant resistance had to be 
9'99182. The resistance that would have been required here, if N had been accurately 
adjusted for the electromagnetic balance, is thus 
9-97772-f ~ X -01410 = 9-97890. 
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