238 Tables 245-247. 



RADIATION CONSTANTS. 

 TABLE 246. — Radiation Formula and Oonstants 2or Perfect Radiator. 



The radiation per sq. cm. from a " black body " (exclusive of convection losses) at the temper- 

 ature T° (absolute, C) to one at f is equal to 



/= 0- ( r4 _ /4) (Stefan-Boltzmann) ; 

 where (r= i. 277X10-12 gramme-calories per second per sq. centimetre. 

 = 7.66 X 10-" " " " minute " " " 



= 5.32 X 10-12 Tjvatts per sq. centimetre. 

 The distribution of this energy in the spectrum is represented by Planck's formula : 



where /;^ is the intensity of the energy at the wave-length X (X expressed in microns, /u) and e is 

 the base of the Napierian logarithms. From Kurlbaum's value of the difference of the total 

 energy radiated from black bodies at 100° C and 0° C,/ioo — /o = 0.0731 watts per square cen- 

 timetre (whence the above value of <r) and Xm»i7"= 2930 (the mean of Paschen's and Lummer's 

 values), the following constants have been calculated (see Planck, Ann. d. Phys. 4, p. 562, 1901) : 



gram. cat. ,„„ , , . . watts 



Ci = 8.813X108 for /in' 



•^ -' sec. cm.' 



14550 for X in microns (/u) 



= 3.688 X 10^ for /in 



/m. 



2.869 X lO-w T^ for /in " ^^^/Jl ' = 1.200 X \Q-^^T^ for/m "—^ 



sec. cm 

 Xm«x T= 2930 for X in microns (/*). 



TABLE 246. — Radiation In aranune-Calorlea per 24 Hours Irom a Perfect Radiator at t° to an at30> 



lutely Cold Space (-273° C). 

 Computed from the Stefan-Boltzmann formula ( Ekholm, Met. Z 1902). 



TABLE 247. — Values of Ja for Various Temperatures Centigrade. 



