220 Proceedings of the Asiatic Society. [Sepr. 
exccedingly unsensitive for small differences, and also with the 
‘‘intensity” coil 30, 40, or 50 cells all produce nearly the same 
deflection (90°) so that it is impossible practically with this galva- 
nometer to compare the electromotive forces, or to find the inter- 
nal resistances of large batteries. 
What therefore is required is an instrument which will give 
independent accurate measurements in absolute units of the electro- 
motive force and internal resistance of any battery. Such an 
instrument will be still more valuable if it be simple, portable, 
and tolerably cheap. All these requirements have been fulfilled 
in the little galvanometer arranged by Mr. Schwendler, and which 
therefore I have considered of sufficient interest to bring before the 
notice of this Society. This galvanometer that I have on the 
table is a tangent galvanometer the bobbin of which is wound with 
two coils one of thick wire and having a resistance of about one 
Siemens’ Unit, and the other of thin wire and having a resistance 
of about 100 Siemens’ units. Forming part of this instrument are 
two resistance coils of 200 and 2000 Siemens’ units respectively. 
The 200 coil can be placed or not at pleasure in circuit with the 
thick galvanometer coil, and similarly the 2000 resistance coil with 
the thin galvanometer coil. 
To (1) (see pl. iv,) is attached one end of each of the coils. 
To (2) the other end of the thick coil. 
To (3) the other end of the thin coil. 
To measure the Resistance of a Battery. 
Join the two poles of the battery to the two binding screws 
respectively of the galvanometer, and make the following observa- 
tions, in each case the mean of the readings with + and — currents 
to be taken. 
Plug up holes marked A and 200: then the battery, and the 
thick coil only are in circuit. Let the deflection of the needle be a°. 
Remove plug from hole marked 200, but leave plug in hole 
marked A: then the battery, the thick coil, and a resistance of 200 
8. U. are incircuit, Let the deflection be 0°. 
Let R be the internal resistance to be found of the battery, 
then 
200 tan 6° 
>> tanw — tanv° 
R 
— 1 Siemens’ Units. 
