16 A. W. Wittowski on the 



Initial cooling - 0894 degree per minute. 



Final „ 0-0195 „ „ 



Mean „ 0*0544 „ „ 



This mean value I accept as determining the external cooling 

 influence during the principal period of the experiment, when 

 the gas current is flowing. I have found that this simple 

 mode of reckoning gives nearly identical results with the 

 more elaborate method of calculating the corresponding cor- 

 rection which has been proposed by Regnault. It seems, 

 moreover, that a more laborious determination of the external 

 heating or cooling effect would be useless, on account of the 

 following anomaly, which presented itself in a more or less 

 marked degree in every experiment : — The transition from 

 the rapid fall of temperature, caused by the cold gas-stream, 

 to the less marked cooling observable during the final period, 

 is always preceded by a slight depression of temperature (as 

 in the preceding example) ; in experiments at high tempera- 

 tures the phenomenon is exactly reversed. Undoubtedly 

 these anomalous variations of temperature are caused by the 

 fact that the direct conduction of heat (or cold) from the 

 heater to the calorimeter is slightly modified by the gas- 

 current itself. This disturbing cause did not escape the 

 attention of Regnault (/. c. pp. 83, 211), but he did not suc- 

 ceed either in getting rid of it, or in taking it into account. 

 Some uncertainty thus remains in every determination of the 

 specific heat. 



In the foregoing example I considered the movement of 

 heat as finished at the end of the 14th minute. The initial 

 and final temperatures of the calorimeter are thus : — 20*152 

 and 14*523 : when corrected with regard to the temperatures 

 of the stem (t and if) they are : — 20*162 and 14*511, whence 

 the total fall of temperature =5*648. From this there is to 

 be subtracted the fall of temperature caused by external 

 influences (0*0511 per minute), the amount of which is : — 

 4x0*0511 = 0*218. Thus we obtain the corrected fall of 

 temperature =5 C *430. 



As regards the initial temperature of the air, it is equal to 

 -103*50 + 2*01=— 101°*49, because the mean deflexion 

 30*15 millims. on the galvanometer-scale corresponds to a 

 gain of 2*01 degrees. The final temperature of the gas is to 

 be calculated by taking the arithmetic mean of the tempera- 

 tures of the calorimeter at the beginning (20*16) and at the 

 end of the current ; the latter we find on the temperature- 



