114 Conduction o1 Heat along Pipe through whicJi Gas Flows. 



be attached to this, in view of the fact that in the present 

 experiments I have made no serious attempt to reproduce 

 Regnault's conditions. A measurement of the minimum 

 value of BJB 2 on the apparatus actually used by Regnault 

 would probably, when used in conjunction with the values of 

 A and B, found by him, cause his observations to lead to 

 values of the specific heats much nearer the values now 

 generally accepted *. 



It may be remarked that in such an experiment as that of 

 Hegnault, a knowledge of the temperature distribution along 

 the pipe would lead to an estimation of the correction for 

 radiation from the pipe, as well as conduction through it, 

 without any independent measurements of the emissivity of 

 the surface, for suppose suffix a refers to the heater and 

 suffix b to the calorimeter, and suppose that dashed letters 

 refer to the case where no gas flows, and undashed letters 

 to the case where the gas is flowing. If H is the total heat 

 given out by the gas per minute due to its fall from the 

 temperature of the heater to that of the calorimeter, Q the 

 heat received by the calorimeter per minute, including the 

 portion which is afterwards radiated from the calorimeter, 

 6 the mean excess temperature of the pipe above its sur- 

 roundings, as determined from the curve, p the quantity by 

 which 6 must be multiplied in order to obtain the heat 



d9 

 radiated from the pipe, and k the quantity by which — -=- 



Clth 



must be multiplied in order to obtain the heat conducted past 

 any cross-section of the pipe per minute, we have, when gas 

 is flowing, 



M$< *M»). + * ■;■•;» 



When no gas is flowing through the pipe we have, 



-*©: +o; -* » 



AtX - AM - • ■ • w 



where A is Regnault' s constant, measured in the manner 

 adopted by him and M is the thermal capacity of the calori- 

 meter and contents. The temperature gradients are all known 

 from the curves, thus (3) gives k, p is obtained by substituting 



* The alteration of the radiation from the pipe caused by the flow in 

 Regnault's experiments was probably small, as owing to the short length 

 of the pipe the whole radiation would, be small. 



