246 
MR, J. E. PETAVEL OX THE HEAT DISSIPATED BY A 
the outer surface of each cylinder will be j)i’oportional to the thermal resistance. 
By plotting the temperatures in terms of the volume of the successive cylinders, 
integrating the curve and dividing by tlie total volume, we obtain the average 
temperature of the gas. This works out as 15 per cent, of the temperature of the 
radiator if we take the temperature of the enclosure as the zero of our scale. 
The same ratio experimentally determined is about 6 per cent. This relatively 
low value is accounted for by the fact that each gaseous particle does not only part 
with its heat to the succeeding one, but streaming upwards, comes sooner or later in 
contact with the upper wall of the enclosure. 
A Numerical Couipctrison of the Heat dissipated by Conductivity in Solids and, 
by Eniissivity in Cases. 
Let us now consider the numerical values of the total eniissivity obtained at high 
pressures. At 160 atmospheres, for instance, in air the eniissivity is (see formula (ii.)) 
E = 0-006912 + 0-000004732 A 
Thus at 160 atmosjiheres air dissipates heat at the same rate as a body having a 
conductivity 
K = 0-0011 (1 + 0-00069 .9), 
therefore at about the same rate as glass (K — 0-001) or plaster of Paris 
(K = 0-0013). 
The conductivity of water is about the same— 
K = 0-0012 (1 — ad), 
but in this case the comparison is not a fair one, for placed in similar circumstances 
convection would also come into play, causing the total loss of heat to be much 
greater. 
Hydrogen at 120 atmospheres behaves like a body having a conductivity 
K = 0-00237 (1 - 0-00072 d). 
Finally tlie eniissivity in liquid carbon dioxide is about 0-2, which would corre¬ 
spond to a conductivity of 0-03, therefore higher tlian mercury or bismuth. The 
conductivity in liquid nitrous oxide is nearly the same. Near the critical tempera¬ 
ture the emissi^■lty in the liquids rises very rapidly ; it falls again instantaneously to 
less than one-tenth of its former value when tlie gaseous state is i-eached. 
A point of some interest which was observed during the course of the work was 
the gradual change in the phenomenon of the decomposition of nitrous oxide. At 
a pressure of 1 atmosphere the decomposition was very slow and more than half 
an hour had elapsed before the change was anything like complete. 
