BETWEEN THE FREEZING AND BOILING-POINTS. 
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adjusted for a change of water flow in the calorimeter, so as to produce the same rise 
of temperature. 
If X 0 is the reading of the potentiometer for the balance point of the Clark cell, 
X x potentiometer reading for difference of potential on calorimeter, 
X 2 the same for resistance R, 
e the E.M.F. of Clark cell, 
R the value of the resistance, 
then E, the potential across the calorimeter, is Xj/Xq X 2e, where the two Clark cells 
are used in series. 
Clark cells. 
Also the current C in the circuit is X 2 /X 0 X 2e/R, from which we get the total 
watt energy per second supplied to the calorimeter, when the conditions have become 
steady, and used in heating the water, 
EC = 
XjX/4 
X 0 2 E ’ 
The experimental error involved in the measurement of EC will depend on the 
accuracy of the measure of X x , X 2 , and X 0 and on the constancy of e and R. 
Sec. 3 a.—Clark Cell. 
Some time previous to my undertaking the present series of experiments, I made a 
careful study of the Clark cell with Professor Callendar in order to become more 
conversant with its behaviour, as well as to devise, if possible, a more reliable form of 
cell than the one in vogue at that time. The result of this work has already been 
