along a Pipe through which Gas is Flowing. 113 



heat loss per square centimetre from the sides *. At the 



d 2 

 point C on the curve -j— 2 = 0, which means that at the pipe 



is gaining as much heat from the gas as it is losing by 



d?d 

 radiation from its surface. At points to the left of C -^-^ 1S 



ax 1 



positive, meaning that the pipe in this region is taking less 



heat from the gas than it is radiating from its surface. At 



d 2 . . 



points to the right of C, -j-g is negative, meaning that, owing 



to the greater difference in temperature between the gas 

 and the pipe and the lower temperature of the latter, 

 the pipe is taking in more heat from the gas than it is 

 radiating from its surface. The smallness of the supply of 

 heat from the gas to the pipe in the immediate vicinity of the 

 heater results in 8i/8 2 f° r that region being larger than it is 

 a little farther along the pipe. On the other hand, at greater 

 distances from the heater 8i/8 2 starts to increase again, since 

 the pipe must enter the calorimeter at the temperature of 

 the latter. The minimum value of 8j8 2 is to be found neither 

 too near nor too far from the heater. 



Now let us consider what fraction of the constant A 

 occurring in ftegnault's correction formula should be taken 

 in a specific heat determination with the present apparatus. 

 Consider any point P of the pipe. Let H be the heat con- 

 ducted past this point per minute when no gas is flowing, and 

 let AH be the amount which is radiated from the pipe between 

 P and the calorimeter. The amount of heat entering the 

 calorimeter is H — AH. When gas flows through the pipe, 

 the amount of heat conducted past P per minute is HSj/Sg, 

 and since the average temperature of the pipe between P and 

 the calorimeter is higher than when no gas was flowing, the 

 amount of heat entering the calorimeter exceeds that which 

 the gas has lost in its fall in temperature from the heater to 

 the calorimeter, by an amount which is less than HSt/Sg — AH, 

 and is therefore certainly less than (H — AH)o\/S 2 . Hence 

 the ratio of the amount of heat which gets from the heater to 

 the calorimeter solely through the pipe when the gas is 

 flowing, to the quantity which gets through when no gas is 

 flowing, is certainly less than the minimum value of 8J8 2 for 

 the whole pipe, which in the present case amounts to about 

 0*45. It is interesting to observe that this is just about the 

 value necessary to bring Regnault's experiments into agree- 

 ment with my own, though, of course, no great significance can 



* It is supposed that the pipe is thin-walled, so that there is no 

 appreciable radial temperature variation. 



Phil. Mag. S. 6. Vol. 25. No. 145. Jan. 1913. I 



