RADIATION OF HEAT BY GASEOUS AND LIQUID MATTER. 
217 
by a second plate of rock-salt. The thermo-electric pile occupied its usual position at 
the end of the tube, the compensating cube, however, being abandoned. For the sake 
of convenient reference, I will call the compartment of the tube most distant from the 
pile, the first chamber, and that adjacent to the pile, the second chamber. An outline 
sketch of the arrangement is given in fig. 3. 
Fig. 3. 
The experiments were conducted in the following manner: — Both compartments 
being exhausted and the needle at zero, the gas was allowed to enter the first chamber 
through a gauge-cock which made its time of entry 40 seconds. The second chamber 
was preserved a vacuum ; the gas on entering the first chamber was dynamically heated, 
and radiated its heat to the pile through the vacuous second chamber ; the needle 
moved and the limit of its excursion was noted. The first chamber was then exhausted 
and carefully cleansed with dry air. The second chamber was filled with the same 
gas, not with a view to determine its dynamic radiation, but to examine its effect 
upon the heat radiated from the first chamber. The needle being at zero, the gas was 
again permitted to enter the first chamber exactly as in the first experiment, the only 
difference between the two experiments being, that in the first the heat passed through 
a vacuum to the pile, while in the second it had to pass through a column of the same 
kind of gas as that from which it emanated. In this way the absorption exerted by 
any gas upon heat, radiated from the same gas, or from any other gas, may be accu- 
rately determined. Finally, the apparatus being cleansed and the needle at zero, the 
gas was permitted to enter the second chamber, and its dynamic radiation from this 
chamber was determined. The intermediate plate of salt S' was shifted, as in the former 
experiments, so as to alter the lengths of the two chambers, but the sum of both 
lengths remained constant as before. 
In the following Tables the three columns bracketed under the head of “ Deflection,” 
contain the arcs through which the needle moved in the three cases mentioned ; 1°, 
when the radiation from the gas in the first chamber passed through the empty second 
chamber ; 2°, when the radiation from the first chamber passed through the occupied 
second chamber ; and 3°, when the radiation proceeded from the second chamber. 
2 G 2 
