110 Dr. W. F. G. Swann on the Conduction of Heat 



with the theoretical value calculated from J. Joly's measure- 

 ments of the specific heat at constant volume, give the specific 

 heats of these gases about 2*5 per cent, higher than the 

 values found by Regnault and many other investigators who 

 followed him. In view of the great care with which 

 Regnault's experiments were performed, it is natural, 

 accepting the modern values as correct, to look for the 

 explanation of the discrepancy as the outcome of some error 

 inherent in the method adopted by Regnault. In my paper 

 on the Measurements of the Specific Heats of Air and 

 Carbon dioxide *, I advanced a suggestion to account for 

 the error, and the object of the present paper is to record a 

 simple experimental verification of that suggestion, and, 

 incidentally, to point out how the error (which is a laro-e 

 one) may be estimated in any similar experiment in which it 

 occurs. 



Reviewing briefly the point in question, it will be re- 

 membered that in Regnault's experiments the alteration A0 

 in the temperature of the calorimeter per minute due to 

 radiation and to conduction through the pipe connecting 

 the calorimeter to the heater, was written in the form 

 A# = A — B#, where 6 is the excess of the temperature of the 

 calorimeter over that of the room. The term A corresponds 

 to the heat conducted through the connecting pipe from the 

 heater to the calorimeter, and B# to the heat loss by radiation 

 from the calorimeter. Each of these terms corresponded to 

 about 5 per cent, of the total energy supplied to the gas per 

 minute. Reonault measured the constants A and B bv notino- 

 the rate of rise of temperature of the calorimeter before and 

 after the gas had passed through it. The error in question 

 arises in assuming that the constant heat conduction through 

 the pipe is the same when gas is flowing as when no gas 

 is flowing. In fact, the hot gas keeps up the temperature of 

 the pipe in the vicinity of the heater, and reduces the 

 temperature gradient there. The result is that less heat is 

 conducted from the heater into the pipe when the gas flows 

 through, than when no gas is flowing. Of course, a great 

 deal of heat is conducted by the pipe into the calorimeter 

 when the gas is flowing, but the greater part of this comes 

 from the gas itself. The fact that the average temperature 

 of the pipe is higher when the gas is flowing also results in a 

 greater radiation loss from the pipe. This error acts in the 

 same direction as the other. 



In the present experiment the gas was passed through a 

 wide brass tube packed with copper gauze, and immersed in 

 a heating bath provided with a stirrer. The wide brass tube 

 * Phil. Trans., A. vol. ccx. pp. 190-238. 



