

HEAT PRODUCED BY THE COMPRESSION OF A_GAS. 297° 
cate galvanometer, and a small thermo-electric battery arranged so that one set of 
the solderings might be within the tube on the side of the entering current of air, 
and the other set within the tube on the side of the current from the orifice. The 
tube on each side of the orifice would need to be bent so as to bring two parts of 
it, at small distances from the orifice on each side, near enough one another to 
admit of the battery being so placed. The only difficulty I can perceive in the 
way of making the necessary arrangements is what might be experienced in 
fitting the two ends of the battery air-tight into the two parts of the tube. It first 
occurred to me that the little battery itself might be placed entirely within the 
tube, and the difference of pressure kept up in the two parts by the middle of the 
battery being fitted nearly air-tight in the tube, by means of wax, or otherwise ; 
but this arrangement would not be satisfactory, as portions of the bars of the 
battery, if not the ends themselves directly, would be altered in temperature, even 
if Mayer’s hypothesis were rigorously true, on account of the rushing of the air 
among them. No part of the battery ought to be exposed to the rushing of the 
air in the neighbourhood of the orifice, and therefore the middle of the battery 
would have to be external to the tube, the ends being cemented into the tube by 
some indulating cement sufficiently strong and compact to hold perfectly air-tight 
on the side where the pressure is different from the atmospheric pressure. By 
such means as these I think a very satisfactory series of experiments might easily 
be performed to test Mayer’s hypothesis for air through a very wide range of 
temperatures. 
18. Should the differential method of experimenting just described indicate 
any difference of temperature whatever on the two sides of the orifice, Mayrr’s 
hypothesis would be shown to be not exactly fulfilled, and, according as the ait 
leaving the orifice is found to be warmer or colder than the entering air, we 
should infer that the heat absorbed, when air expands at a constant temperature, 
is less than or greater than the mechanical effect produced by the expansion. 
19. Calorimetrical methods, like those used by JouLE, might then be followed 
for actually determining the heat emitted or absorbed by the air.in the neigh- 
bourhood of the orifice, or in the second spiral, in acquiring the temperature of 
the air in the entering stream, and by careful experimenting, it is probable that 
excessively accurate results might be thus obtained for a wide range of tem- 
perature. : 
20. The result of each experiment would be a value of y, in terms of Jouxn’s 
mechanical equivalent; to be calculated by the following expression, derived 
from equations (5) and (6). : 
E 
1+Et¢ 
fh ee  aumemee h 467); 
oe 
Jul fe 
pu Sy 
VOL. XX. PART Il. 4uL 
