1871.] Proceedings of the Asiatic Society. 217 
‘ 
12. Nore on rue Error or THE Caxcurra SranparD Barome- 
TER, COMPARED WITH THOSE oF Kew anp GreENwicu,—by H. 
F, Buanrorp, Esa. 
This short paper will be published in the 4th number of the 
Journal for the current year. 
13. On A ForM or GALVANOMETER SUITABLE FoR THE QUANTI- 
TATIVE MeAsUREMENT oF THE ELxEcrromorivE Force, AND 
Internat Resistance or TeLecRrarn Barrertes,—by W. E. 
Ayrton, Esa. 
(With plate IV.) 
The efficiency of a galvanic battery depends on the magnitude of 
two properties it possesses, its electromotive force, or power to send 
a current, and its internal resistance, or power to impede a current. 
The greater the electromotive force the greater the current sent if 
the whole resistance in circuit remains the same, and the greater 
the internal resistance of the battery the less the current sent, 
other things remaining the same. 
It is therefore of great practical importance in Telegraphy to 
be able easily to measure the electromotive force and internal re- 
sistance of a battery so as to see from day to day that the former 
does not diminish, and that the latter does not increase. 
I will first examine the way in which this has been practically 
done up to the present time, and point out the objections there 
exist to this method. 
A galvanometer was employed, on the bobbin of which were 
wound two coils, one of a comparatively high resistance, called 
the ‘‘intensity” coil, and the other of a comparatively low 
resistance, called the ‘quantity’ coil. The electromotive force 
was measured by observing the deflection produced when the 
coil of high resistance was inserted between the battery poles ; 
and the internal resistance could be found by comparing the de- 
flections produced when the coils of high and low resistance 
were respectively used. In some instruments the low resistance 
galvanometer coil was dispensed with and instead the high re- 
sistance coil was shunted. 
