230 
MR. J. E. PETAVEL ON THE HEAT DISSIPATED BY A 
experimentally treated in many dilierent ways. The rate of cooling of a body 
of known specific heat has been directly measured by Dulong and Petit, Xare, 
Macfarlane, Nichol, Stefan, Brush, Bottomley, Winkelmann, Kundt, and 
Warburg, Eckerlein, Graetz, &c. By Christiansen’s method, the value of the 
conductivity has been derived from the fall of temjierature per unit length along 
the axis of a cylinder carrying a constant flow of heat. Schleierhacher, Sala, 
Ayrton, and others have preferred to measure the quantity of electrical energy 
dissipated per unit time. These experiments have, however, been carried out at or 
below the atmosjiheric pressure, and the question of the heat dissipated in gases at 
high pressures has rarely lieen touched upon. From the ordinarily accepted 
principles of the Kinetic theory of gases, it may be shown that the conductivity 
of any perfect gas is independent of pressure. The experimental work of Stefan 
and of Kundt and Warburg has gone far to confirm this law as far as ordinary 
pressures are concerned. It will be seen, however, that at higher pressures, only a 
small proportion"^ of the loss of heat is due to conductivity, and the question as to 
whether the theoretical law is strictly correct, though well worth investigation, is 
not of primary importance. 
For the above reasons the present work has been restricted to a study of the 
total heat dissipated at exceptionally high pressures and temperatures. 
The Apparatus. 
The method employed is the same as that described in 1898 in the first part 
of the present series. It will therefore be sufficient to recall here that the measure¬ 
ments are made by means of a wire, calibrated as an electric thermometer according 
to Callendar’s system, and heated by an electric current, the readings of the 
current passing through the wire, and the electromotive force at the potential 
terminals, being made by a potentiometer. The standard resistance had a tempera¬ 
ture coefficient of 0•000003, and as it was efficiently cooled, the small outstanding 
variations in temperature involved no correction. 
The results of the comparison of this coil (O’Ol ohm, Wolff, No. 779) with 
two standards of reference (O'l ohm. No. 709, and O'OOl ohm. No. 834) are given 
below :— 
On the 27th September, 1895 
On the 3rd March, 1900 
Standard OT ohm 
in terms of the 
working standard, 
10-005 
9-985 
Standard O'OOl ohm 
in terms of the 
working standard. 
0-10004 
0-09991 
Tire original resistance of the working standard was, according to the Beichsan- 
stalt Ce)-tificate, 0-0099967 at 24°-9 C. and 0-0099965 at 16‘^-5 C. On the 3rd 
March, 1900, its resistance Jiaving increased aliout 0-16 per cent., was therefore 
* About jlyth at 160 atmospheres. 
