00 M. E, Wiedemann on the Specific Heats of Gases. 



In order to estimate the heat radiated to and from the 

 calorimeter, as also that carried away by currents of air, we 

 make the assumption (justified by the smallness of the dif- 

 ferences of temperature) that this is proportional to the differ- 

 ence of temperature between the calorimeter and its surround- 

 ings. We shall designate the rise of temperature per minute 

 brought about by radiation &c, for a temperature-difference 

 of 1 between calorimeter and surroundings, by a. The 

 measurements taken before and after the gas was allowed to 

 flow through the apparatus serve as data for calculating the 

 values of « and k. 



Let T represent the mean temperature of the calorimeter 

 during the initial period, T x the mean temperature during the 

 final period ; let t represent the temperature of the surround- 

 ings ; m and m 1 the increase of temperature of the calorimeter 

 per minute during these periods ; then 



— (T — t)ol + h = m, 



— (T l ~r)u-\-k=:m 1 ; 



hence we deduce 

 and 



a = 



Tj-T 



k = 7n + ^ T~7£ 



It may readily be shown that it is not really necessary to 

 know the temperature of the surroundings (that is, the value 

 of t), inasmuch as it remains constant throughout the experi- 

 ment. 



For this purpose let us suppose that the rise of temperature 

 is uniform so long as gas passes through the calorimeter (and 

 with a constant flow of gas this is almost exactly true), and let 

 us calculate, on this supposition, the mean correction which it 

 is necessary to apply to the observed temperature for each 

 minute of time. 



Let the temperature of the calorimeter at the moment when 

 the gas begins to pass through be represented by t u and at the 

 moment of closing the stopcock by t 2 . Then the mean tem- 

 perature during the experiment is 



h + t 2 



2 

 The correction is then 



_Jh±h- T \ +k , 



