92 
DE. JOULE ON SOME THEEMO-DTNAMIC PEOPEETIES OF SOLIDS. 
2. The apparatus I employed is represented by the adjoining sketch, where a spiral 
spring of tempered steel is seen immersed in the can A. By applying weights to a lever 
connected with the link B the spring could be compressed, and the heat evolved, if any, 
measured by the increase of temperature obsen’ed to take place in the water or mercury 
filling the can. The plan I pursued was to note the temperatui-e successively ; first, two 
minutes after the weight had been laid on; second, two minutes after the weight had 
been removed ; and third, after two minutes more had elapsed. The mean of a mimber o 
these observations taken in succession, gave me,— first, the thermal effect resultmg from 
the laying on of the weight and the atmospheric influence ; second, that of the removal ol 
the weight and the atmospheric influence ; and third, the atmosphenc mfliience 
3. The pressure applied was 318 lbs., which pushed doum the spiral spring IT 36 inch. 
In the following summary of results, each number is the mean of eight or ten obseiwa- 
tions, given in terms of the graduation of a thermometer, of which each degi-ee was 
equal to -0668 of a degree Centigrade. 
First Series. Spring immersed in 8 ozs. of water. 
First experiment . 
"Weiglit laid on. 
. . ^-548 
Weight taken off. 
-•568 
Atmospheric influence. 
-•560 
-•012 
Second experiment . . 
. . --009 
-•023 
Third experiment . . . 
. . +-282 
+ •271 
+ -2o2 
Mean ..... 
. . --092 
-•107 
— ■107 
Second Series. 
Spring immersed 
in 7 lbs. of mercury. 
First experiment . . . 
Weiglit laid on. 
. . +T80 
Weight taken off. 
+ •175 
Atmospheric influence. 
+ •169 
Second experiment . . 
. . -f-066 
+ •092 
+ •059 
Third experiment . . . 
. . -f-041 
+ •039 
+ •020 
-•053 
Fourth experiment . . 
. . --060 
— •059 
Mean ..... 
. . +-057 
+ •062 
+ •049 
Mean of both series 
. . ~-032 
oo 
CO 
o 
I 
— •041 
4. The capacity for heat of half a pound of water being about tuice as great as that 
of 7 lbs. of mercury, I have divided the mean result of the second series by two, before 
combining it with the first series in a general mean. The mean of both serms therefore 
represents the thermal effect in the capacity of half a pound of water. It indicates, on 
subtracting the effects of the atmosphere, a heating effect of -009 after lapng on the 
weight, and a heating effect of -003 on taking off the weight. The highest of these 
numbers represents a temperature less than one thousandth of a dep-ee Fahr. 
5. Now the actual force expended in the compression of the spring was 14-268 foot- 
pounds, which is equivalent to 0°-037 Fahr. in half a pound of water, a thermal effect 
which would have been made manifest with the greatest facility. Hence it uas 
