JAN. 19, 1923 WHITE: ELECTRIC HEATING OF CALORIMETERS 19 
| Indirect Method for Finding the Thermal Head 
The conditions on which the calculation method has to be based are 
as follows: 
It will be convenient to treat first the case where the thermal headis 
practically zero at the beginning of the heating. If OA in fig. 1 repre- 
sents the course of the calorimeter temperature before the heat is 
turned on at the time of A, for the time 7, = AB’, then ABM may 
represent the temperature corresponding to the energy which has been 
given to the calorimeter. The temperature read is caused to vary 
from this simple scheme by two things, first the lag, and then the ther- 
CALORMME LA | LMPVL RATE 
TIME 
Fig. 1 
mal leakage. The lag alone would make the temperature follow the 
line AHFG, which, if the lag is not unusually large, may with quite 
negligible error be taken as coincident between two points, # and F, 
with a line CD, parallel to AB, and at a point G with BM. Then 
_ the horizontal distance AC, = BD, represents the time Ly, the lag 
of the calorimeter temperature behind the energy supply. The shaded 
areas ACE and FDG are equivalent, hence the mean temperature and 
consequently the mean thermal head will be just the same if the line 
followed is ACDM, and this will be taken as the result of the heating. 
This temperature pattern is further modified by the thermal leakage 
which it itself causes. The modification is merely a fall of tempera- 
ture everywhere proportional to the actual thermal head, and giving 
that when superposed on the pattern ACDM., 
