78 



INFRA-RED EMISSION SPECTRA. 



trum, indicating a much higher temperature (if the radiation is purely 

 thermal) than would be the case if the emission bands at 2 to 4 /z were 

 the more intense. 



100 



90 



80 



(0 



60 



m 



c 



.2 



4-0 



30 



zo 



10 



A 



n 



620 



r x 3zo 



^J 



rn 1 r-| l 11 1 11 1 11 rn r i | v \ ' i i 



1.540 1.535 /.530 1.525 1.520 



95 



\) 



\A 



co 2 



~r 



~r 



-I \ 1 1 



1.5 Z 3 4JU 



/I 0.75 



Fig. S4- Emission of potassium (Moll) 



RADIATION AT ROOM TEMPERATURE. 



The distribution of energy in the spectrum of a complete radiator has 

 been determined for temperatures varying from 373 to 1800 abs., and 

 the constant in the "displacement law" -^ max T=A has been found to be 

 2930 (2940, Lummer and Pringsheim; 2920, Paschen). For bright plati- 

 num the value of this constant is about 2630. The measurements of 

 Lummer and Kurlbaum 1 show that at low temperatures (492 abs.) the 

 emissivity of iron oxide is 0.3, while bright platinum is only about 0.04 

 that of a complete radiator at the same temperature. The spectral distri- 

 bution of radiation at low temperatures has been given but little attention. 

 This is due in part to the impracticability of reducing the temperature of 

 the radiation meter below that of the room. The problem is therefore 

 reversed, in that the radiation meter (bolometer, radiometer, or thermopile) 



1 Lummer & Kurlbaum: Verb. Phys. Ges. Berlin, 17, p. no, 189S. 



