MR. J. P. JOULE ON THE AIR-ENGINE. 
73 
of the apparatus will be better understood by a reference to fig. 5, in which a section 
of it is represented, a being the upper, b the lower vessel, and w the surface of the 
water in the latter, xx are a pair of wooden pincers by means of which the india 
rubber tube could be compressed so as to prevent, when desired, any communication 
between the air in the two coils of piping. Referring again to fig. 4, g is a gas-lamp 
to maintain the water in the upper vessel at a constant high temperature, and J is a 
tall jar filled with coarsely pounded chloride of calcium, in passing through which 
the air was entirely deprived of aqueous vapour ; a length of vulcanized india rubber 
tubing, p, connects the coil of the lower vessel with a good air-pump, each barrel of 
which was found to have a capacity of 12'77 cubic inches. The temperature of the 
pump could be ascertained by means of a small thermometer, the bulb of which was 
kept in contact with one of the barrels. 
The method of experimenting was as follows: — The lower vessel being filled with 
cold water, and the upper with water raised to about 190°, their exact temperatures 
were read off", with the usual precautions, from the scales of delicate and accurate 
thermometers. The pump was then worked at a uniform velocity for tvi^enty-six 
minutes, the water in the lower vessel being agitated from time to time by a stirrer. 
The examination of the barometer and thermometers a second time occupied four 
minutes more ; so that the whole time occupied by each experiment was exactly half 
an hour. The pincers were now applied so as to cut off all communication between 
the air in the two coils, and the effect of the various causes of a change of tempera- 
ture in the lower vessel, unconnected with the current of heated air, was observed 
during another half-hour. Experiments of both the above kinds were repeated 
several times with the results tabulated below. 
I may remark in this place that I had ascertained, by preliminary experiments, 
that the air passed from the coils of the vessels sensibly at the temperatures registered 
by the thermometers plunged into the surrounding water. 
Series I. — Pump worked 26 ', at the rate of twenty-four strokes per minute. 
No. of 
Experi- 
ment. 
Source of calori5c effect. 
Height 
of Ba- 
rometer. 
Tempe- 
rature of 
Baro- 
meter. 
Tempe- 
rature of 
Air- 
pump. 
Tempera- 
ture of 
upper 
vessel. 
Tempe- 
rature 
of the 
room. 
Temperature of the lower 
vessel. 
Increase 
of tem- 
perature. 
Commence- 
ment of Ex- 
periment. 
Termination 
of Experi- 
ment. 
1 
1 
2 
2 
3 
3 
4 
4 
5 
Radiation 
O 
0 
O 
46-081 
46-188 
46-497 
46-785 
46- 948 
47- 068 
47-197 
47-283 
47-455 
41-270 
41- 814 
42- 802 
4.3-304 
44-246 
44- 694 
45- 590 
45- 983 
46- 856 
41- 814 
42- 802 
43- 304 
44- 246 
44- 694 
45- 590 
45- 983 
46- 856 
47- 211 
0-544 
0-988 
0-502 
0-942 
0-448 
0-896 
0-393 
0-873 
0-355 
Heated air and radiation ... 
Radiation 
30-195 
46 
49-3 
189-28 
Heated air and radiation ... 
Radiation 
30-205 
46-75 
50-3 
189-43 
Heated air and radiation ... 
Radiation 
30-22 
47-5 
51-1 
189-89 
Heated air and radiation ... 
Radiation 
30-235 
48- 
51-7 
194-85 
Mean. 
Mean. 
Heated air and radiation ... 
Radiation 
30-214 
47-06 
50-6 
190-862 
46-831 
46-836 
43- 949 
44- 153 
44-874 
44-601 
0-925 
0-448 
MDCCCLII. L 
