376 N. D. C. Hodges—Determining the resistance of a battery. 
y Mr. Mance’s method, with the same value of R,, the 
value obtained was B=-357. The above numbers are expressed 
in ohms and fractions of an ohm. My method has the advan- 
tage that many determinations of the battery resistance can be | 
made with the same arrangement of cells. In Mr. Mance’s 
method but one determination can be made without altering 
the arrangement. I have found the following form of Rheocord 
2, eful in these determinations. 
In fig. 2 a and ¢c are two German 
silver wires, with a slider at d which 
has a binding screw; between the 
' wires is a mirror 4 with a scale upou 
it, or at its side, in order to avoid 
= is thus possible, by making a large 
variation in y, to measure small re- 
sistances a little larger than the 
4 small resistance og; thus employ- 
[\ ing the correct principle of working 
rom the greater to the less. 
By disconnecting the r®sistance op at m and p and joining 
mn, it will be readily seen that the combined resistance of the 
circuit dnmd is one-half that of nd alone. It is often desir- 
able to reduce the resistance in this manner 
e changes in the combined resistances can of course be 
readily calculated from the expression A = , where x and 
d=6 
7 represent the two branches of the circuit. I have often found 
it advantageous in measuring large resistances to shunt them, 
