Comparison of Formulae for Total Radiation. 



443 



the room in which the measurements were made. The ordi- 

 nates are to be read in units of deflection on a scale such as 

 was employed in the galvanometer readings representing 

 radiant energy. For temperature-differences less than 100° 

 these curves are nearly coincident. For high temperatures 

 Stefan's formula gives results that are higher than those of 

 Weber's formula ; but the rate of increase by Weber's formula 

 grows more rapidly, and for a temperature difference of about 

 720°, about that of red heat, the two curves cross each other, 



Fig. 2. 



50000 



? ' W 



45000 



1 1 r 



40000 



1 If 



35000 



i 1 



30000 



II 



25000 



/ / 



20000 



/ // /* 



10000 



JJ/ 



5000 



^^^ 







^-^^^^^ 







100 200 300 400 500 600 700 800 



Curves of radiation for temperatures from 17° to 81 "7° C. 



D. Curve for formula of Dulong and Petit. 

 W. " " " " Weber. 

 S. " " " " Stefan. 

 R. " " " " Rosetti. 



and, from this point on, the indications of Stefan's formula 

 become lower than those of Weber's formula. In this connec- 

 tion we may again refer to the experiments of Schleiermacher, 

 who, by estimating change of temperature through variation of 

 electrical resistance, found the indications of Stefan's formula 

 to be less than the results obtained by experiment. The curve 

 of Rosetti's formula gives a rate of increase in radiation that is 

 about as much too low as that of Dulong and Petit is too high. 



