A. D.C. Hodges— Determining the resistance of a battery. 375 
. , Change _ , Change Strength of Strength of 
in the resistance | in the resistance Indwend = Ego ae 
on breaking. on making. on breaking. 
| 
650 600 00325 "00300 
700 689 00350 "00340 
720 720 “00360 “00360 
720 750 ‘00360 "00875 
700 700 00350 “00350 
850 850 00425 00425 
Care should be taken to send the induced currents to be 
compared in the same direction by means of a pole changer. 
It will be seen from the above table that the equality of the 
Saat on making and breaking can readily be proved by this 
met 
No. VL— On methods of determining the resistance of a bat 
deduced from Pog ge es of measuring t Gattesrst 
Forces ; by N. D. C. H 
In the process of obtaining the ratio between the electromo- 
tive forces of two cells, the expression “hae | is obtained ; 
in which E>H’, R, is the resistance necessary to bring the 
— of the galvanometer G to zero, and 
- is the resistance of the battery to be 
B) tS sured. By introducing a new resist- 
J & 
/ pis Ri in the branch ab, we shall obtain 
| +R'+R,+R, 
the expression j= R,+R, ’ 
* \,¢ in which R, is the new value of R - 
h R, sshd paBoR’ 
Me Wee e+e, R, 
So» If the ratio a becomes —we shall have 
B aig _P+R, i BS nim if 
This expression was niet by sy "Mance in the Phil. Mag., eee 
xli, p. 318, 1871, and is seen to follow directly from P 
orff’s method of measuring electromotive forces. a cy =o 
ing are the results obtained from the expression B= in 
Measuring the resistance of two Grove cells. One Grove eal 
Was opposed to the two whose combined resistance was m 
R, 
ees B 
Ty | ee | ae 
" 5 5144 “BAT 
“ 1 7-140 | “350 
