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Mr. 8. C. Laws on the Thomson Lffect 
V. Experiments with Bismuth. 
Mean diameter of roads = 5°79 mm. 
Mean resistance of rods = 0°0000453 ohms per mm. 
The specific heat of electricity in this metal has been 
previously measured by Batelli*, who found that the value 
is proportional to the absolute temperature, Some observa- 
tions taken are shown in Tables I. and II., from which the 
value of the specific heat of electricity in bismuth at 32°5 C. 
is obtained. 
As explained above, in order to obtain an absolute value of 
the specific heat of electricity, two experiments are necessary, 
and the tables given include results of experiments of each 
kind. 
The first or Thomson effect experiments consist in measuring 
the change of temperature produced by a reversal of the 
current in the rods when there is a temperature-gradient 
along these. 
In Tables—e. g. No. I.—showing the results of these experi- 
ments, H represents the hour at which the observation was 
taken ; y, the vaiue of the current in the compensating 
circuit necessary to counterbalance that in the ‘junction ’ 
circuit when the current, C, indicated at the head of the table 
is flowing in one direction through the rods; y. the corre- 
sponding value of the ae current when the current 
in the rods is reversed ; 6(=y2—) the change in the value 
of the compensating current dae i a reversal of the current C. 
x, and «x, represent the distances from the cold bath at 
which the two junctions of each thermocouple are placed ; 
d@ . 
the values of — for these values of # are found from curves 
dx 
showing the relation between temperature and distances along 
the rods for the currents used in the experiments. 
The values of the correction shown were found in exactly 
the same way as those of the Thomson effect, except that 
they were made when the rods were at a uniform temperature 
throughout. The correction given represents the mean of 
the values obtained. 
In the second or ‘Joule effect? experiments the rise of 
temperature produced by the flow of the current through the 
rods when these are at a uniform temperature throughout 
is obtained. 
In tables referring to this second experiment, e. g. No. IL, 
y, and y. are the values of the compensating current when 
the current C passes first in one rod and then in the other. 
* Batelli, doc. crt. p. 548. 
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