376 Trowbridge and Hayes—Application, ete. 
battery with ten ohms external resistance. Under these condi- 
tions we find at the instant of making circuit a strong current 
which rapidly diminishes within the first five minutes to one- 
sixth of its first strength. ee 
Knowing the distance of the galvanometer from the sensitive 
paper the strength of the current may be calculated by measut- 
ing the distance between the two lines at any instant and pro- 
ceeding as with an ordinary galvanometer and scale. 
From a comparison of the two figures the electromotive force 
may be determined by Ohm’s law, if the distance between the 
lines is measured at the instant the current is made. Then 
knowing the electromotive force, current, and external resist- 
ance, we can readily find the internal resistance. This get 
electromotive force due to polarization, and the — in 
We have selected these photographs as an example of the 
large variations that some batteries present and the conse uent 
usefulness of some such way of studying their action. rom 
measurements upon these photographic charts the variations 1 
s 
be 
coil galvanometer which indicates the gradual heating of 8 
thermopile. a this way the conduction of heat along a bat 
ied, 
_ Jefferson Physical Laboratory, 
