1871. ] Proceedings of the Asiatic Society. 219 
let d be the deflection given by the battery when the “ intensity” 
coil of resistance G is used, and let d’ be the deflection given when 
the “ quantity” coil of resistance G’ is used, then from equation (1) 
we have, since both the coils are wound on one bobbin and the 
magnetic needle is the same in both cases, 
n EB 
d RAG 
ad’ n KE 
where and n’ are respectively the number of convolutions in the 
coils 
nx Gxd—-n xG@Gxd 
nxXd—nXd 
The resistance of different batteries, or of the same battery on 
R= 
different days, can be found in this way and then the ratio of their 
electromotive forces from equation II. This is a very round-about 
way of comparing electromotive forces, but is nevertheless the only 
way in which it can be done with the so-called ‘ intensity” and 
* quantity” galvanometer coils if the battery resistance be large. 
If now the question be to determine simply the resistance of a 
battery when the resistance is small, that of one cell for example, 
then it is impossible to get an accurate result with the ‘‘ intensity” 
and “ quantity” coils, for we see from equation (I) that if R be small 
compared with G, then a small percentage of change in # will 
produce no practical change in d, that is to say, when using the 
‘‘intensity’’ coil the deflection will be practically the same whatever 
the resistance of the battery may be, as long as it is small compared 
with the resistance of the ‘‘ intensity’ coil. 
Therefore with the “intensity” and “ quantity” coils we cannot 
find accurately the resistance of a battery if small, and, secondly, 
we cannot compare the electromotive forces of two batteries without 
previously determining their internal resistances if the internal 
resistances be large. Such an instrument, therefore, for battery test- 
ing as Latimer Clark’s Shunt Galvanometer which is arranged virtu- 
ally on the principle I have been describing does not at all meet the 
requirements of the Indian Telegraph Department. And besides 
the instruments of this description that have been received are 
. 
