336 Messrs. Wright and Rennie on the Determination of 



minutes, the + value meaning loss of heat, and the — sign 

 gain*. 



Millims. per hour. 

 Value of x obtained by first method ^ 



(formula applied to mean values of > —1*00 



MandN) . . ) 



Value of x obtained by second method. 

 Observed rate of alteration be- "^ 



fore experiment commenced —4*1 ! ™ _ i -05 



Observed rate of alteration f 



after experiment concluded +2*0 J 



Value of x obtained by third method. 

 Calculated rate of alteration at ^ 



commencement . . . .—4*0 VMean =— 1'02 

 Ditto at close + 1-95) 



Average —1*02 



Hence the radiation -correction for the eighteen minutes 



1 8 

 during which the experiment lasted is — ^ x 1*02= —0*31. 



43. The above correction, however, is not the only one to 

 be applied ; for the water in the voltameter gets heated more 

 quickly than the calorimeter, and after the end of the experi- 

 ment some time is required for the heat retained in the volta- 

 meter to become uniformly diffused throughout the calori- 

 meter by passage through the glass wall of the voltameter. 

 It was found that 6 or 7 minutes sufficed to bring about 

 perfect equalization of temperature; so that during the first 

 5 minutes or so the temperature of the calorimeter slightly 

 rose, and then began to fall again from the cooling effect of the 

 radiation. Accordingly, to determine the true amount of rise 

 in temperature during the experiment, the thermometer was 

 read 8, 10, and 12 minutes after the conclusion — the loss by 

 radiation during these several periods of 8, 10, and 12 minutes 

 being added on to the observed temperature at the ends of 

 these periods severally; the mean of the three numbers thus 

 obtained was taken as the true temperature that would have 

 been observed at the end of the experiment had the heat re- 

 tained in the voltameter been diffused throughout the calo- 

 rimeter at that moment. The loss during these three periods 

 is calculated from the data in the latter two methods just 



* This particular experiment is selected as an illustration because the 

 temperature-corrections detailed in this and the subsequent paragraphs are 

 larger than those in almost any other of the 18 experiments made in all 

 (§46). 



