242 
MR. J. E. PETAVEL OX THE HEAT DISSIPATED BY A 
At one-tenth of an atmosphere and 100° C., we have for the various gases— 
Pressure, OH Atmosphere. Temperature interval, H = 100° 
Heat lost— 
Air. 
Oxyge 
n. 
1 
, Hydrogen. 
Carbon dioxide. 
In C.G.S. 
units. 
In per 
cent. 
In C.G.S. 
units, 
In per 
cent. 
In C.G.S. 
units. 
In per 
cent. 
1 
1 
In C.G.S. 
units. 
In per 
cent. 
i By conduction . . . 
0-00041 
82 
0-00041 
79 
0-00281 
98-6 ! 
0-00028 
64 
By convection . . . 
0-00006 
12 
0-00008 
15 
0-00001 
0-4 
0-00013 
30 
By radiation 
0-00003 
6 
0-00003 
6 
0-00003 
1-0 
0-00003 
6 
Total heat lost = 
0-00050 
100 
0-00052 
100 
. 0-00285 
100 
0-00044 
100 
emissivity 
And if, for the present, we assume the conductivity constant the values at 
100 atmospheres and 100° C. would be—• 
Pressure, 100 Atmospheres ; Temperature interval, S = 100° 
Heat lost— 
Air. 
1 
Oxygen. 
1 
Hydrogen. 
In C.G.S. 
units. 
In per 
cent. 
In C.G.S. 
units. 
In jDer 
cent. 
In C.G.S. 
units. 
In per 
cent. 
1 
1 By conduction . . . 
0-00041 
7-1 
0-00041 
6-7 
0-00281 
.w i 
By convection . 
0-005.30 
92-4 
0-00566 
92-8 
0-01026 
78-4 ' 
By radiation 
0*00003 
0-5 
0*00003 
0-5 
0-00003 
0-2 i 
Total heat lost = emis- 
0-00.574 
100 
0-00610 
100 
0-01310 
100 
sivity 
The result is remarkable; for instance, in the case of air, at one-tenrh of an atmo¬ 
sphere 12 per cent, of the total loss is due to convection, and at 100 atmospheres 
92 per cent, is due to this same cause. The heat lost by convection is in air 100, 
and in hydrogen 500 times greater at a pressure of 100 atmospheres than it is at 
O'l atmosphere. 
For temperature-intervals of several hundred degrees it is iinpossihle experimentally 
to eliminate either of the three effects of convection, conduction, or radiation, but 
the first of the three can be greatly diminished. To this end the apparatus was 
filled with lightly packed glass-wool. The proportion of the total volume actually 
occupied by the glass was 24) })er cent. 
* The loss of heat is expressed in therms per square centimetre of radiating surface, per second per 
degree Centigrade of temperature interval. 
