442 



W. LeConte Stevens — Experimental 



The mean results of Tables VII and VIII are expressed 

 graphically in the curves of fig. 1. Here it is seen that 

 Weber's formula is expressed by a curve (WW) nearly parallel 

 to the axis of abscissas, but with slight irregularities, as might 

 be expected in any representation of experimental results. At 

 no point is the deviation so great as # 5 of 1 per cent. • Stefan's 

 formula is expressed by a curve (SS) which is plainly oblique 

 to the axis of abscissas, the greatest deviation being more than 

 6 per cent. These experiments therefore confirm the result 

 otherwise attained by Schleiermacher, indicating that for tem- 

 peratures but little above that of the atmosphere Stefan's 

 formula gives a rate of increase of radiation that is too rapid, 

 while Weber's formula coincides very closely with the results 

 yielded by experiment. 



Fig. 1. 



~W 



15 25 35 45 55 65 75 85 95 



Curves of deviation for formulas of radiation for temperatures from 30° to 110° C. 



It may be of some interest in this connection to exhibit the 

 application of these formulas to a wider range of temperature 

 difference. For this purpose the constants of each formula 

 have been determined from the data contained in the tables 

 just given ; those of Rosetti's formula being obtained by method 

 of least squares. In fig. 2, the abscissas represent temperature 

 differences from 0° to 800° C, the temperature of the thermo- 

 pile being taken as 17° C, which was the mean temperature of 



