Table 129 4jj 



BLACKBODY RADIATION 



Planck's formula for the spectral radiant emittance 1 W\ of a complete radiator (black- 

 body) is 



tt 



i^x = Cx\- 5 (/ 7 "-l)- 1 (1) 



where X is the wave length, T is the absolute temperature (°K.) and a and c 2 are con- 

 stants. The most probable values of the constants (for X in cm.) are: a Ci = 3.740 X 10"° 

 erg cm. 2 sec." 1 and Ci = 1 4385 cm. °K. This gives W\ in ergs per second per square 

 centimeter per centimeter of wave length. 



Table 129 A 3 gives values of the ratio W<y-\IWo-m as a function of the parameter XT 



(cm. °K.) where Wo-x = S Wx d\ and 0V. (or W) = J°Vx d\. 







Table 129 B gives values of the (total) radiant emittance W computed from the 

 Stefan-Boltzmann law 



W — gT (2) 



where the Stefan-Boltzmann constant a is 5.673 X 10~ 3 erg cm." 8 °K..~ i sec." 1 or 8.132 X 10" u 

 cal. cm." 2 "K." 4 min." 1 The wave length of maximum emittance X ra for a specified tempera- 

 ture is given by Wien's displacement law 



X m T = 0.2897 cm. °K. (3) 



Table 129 C gives the distribution of energy radiated from a blackbody in various 

 wave-length intervals for a few typical earth temperatures, computed from parts A and 

 B of this table. 



1 The energy emitted per unit area and per unit time in the solid angle 2ir steradians (hemisphere). 



2 Birge, R. T., Rev. Mod. Phys., vol. 13, p. 233, 1941. 



3 Miscellaneous Physical Tables, Planck's radiation functions and electronic functions, WPA project 

 sponsored by the National Bureau of Standards, New York, 1941. The values of Ci and c 2 used in 

 this table differ slightly from the accepted values given above. The table is computed with 

 c,= 3.732 X 10- 6 erg cm. 2 sec.- 1 and r 2 = 1.436 cm. °K. 



(continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



