ON THE MECHANICAL EQUIVALENT OF HEAT 



437 



the revolutions and the torsion, so as to compute the work. As I had 

 foreseen, the results in this case were higher than by the other method. 

 At low temperatures the error of the first method was fifteen per cent; 

 but at high, it did not amount to more than about three to five per 

 cent, and probably at very high temperatures it would almost vanish. 



I do not consider it necessary to give all the details of the radiation 

 experiments, but will merely remark that, as the calorimeter was nickel- 

 plated, and as seventy-five per cent of the so-called radiation is due 

 to convection by the air, the coefficients of radiation were found to be 

 very constant under similar conditions, even after long intervals of 

 time. 



The experiments were divided into two groups; one when the tem- 

 perature of the jacket was about 5 C., and the other when it averaged 

 about 20 C. 



The results were then plotted, and the mean curve drawn through 

 them, from which the following coefficients were obtained. These 

 coefficients are the loss of temperature per minute, and per degree 

 difference of temperature. 



TABLE XXXV.* COEFFICIENTS OF RADIATION. 



As the quantity of water in the calorimeter sometimes varied slightly, 

 the numbers should be modified to suit, they being true when the total 

 capacity of the calorimeter was 8-75 kil. The total surface of the 

 calorimeter was about 2350 sq. cm., and the unit of time one minute. 

 To compare my results with those of McFarlane and of Nichol given 

 in the Proc. K. S. and Proc. R. S. E., I will reduce my results so that 

 they can be compared with the tables given by Professor Everett in his 

 ' Illustrations of the Ccntimeter-Gramme-Second System of Units/ 

 pp. 50, 51. 



* [There is no table numbered XXXIV.] 



