128 



INFRA-RED EMISSION SPECTRA. 



of gases. It is possible that for some wave-lengths the thickness of the 

 radiator was not sufficient to emit a saturated radiation, and this may ex- 

 plain why the emissivity at 2.048 p. apparently does not follow the same 

 law as do the other emission bands. In order to have a displacement of 

 the maximum of emission, just as is known for solids emitting continuous 

 spectra, it is necessary that the intensity of the emission at the short wave- 

 lengths increase more rapidly than it does in the long wave-lengths. The 

 2.048 [i isochromatic slants only a little less from the normal than does 



16 



id 



Fig. 96. 



20 22 24 Watts 



Isochromatic radiation curves of oligoclase. 



^=6.082 /<. In this region of the spectrum there is a weak general ab- 

 sorption, while the other wave-lengths are the maxima of selective emission 

 (absorption) bands, and it is possible that what corresponds to the emis- 

 sivity constant a of a complete radiator is different for the two kinds of 

 radiation found in this substance. It is possible that the isochromatic at 

 2.048 n undergoes a sudden change, curving sharply upward, at a higher 

 temperature. The same is true of the platinum isochromatic at 1 ft. In 

 fact, it appears that the emissivity at 2.048 \x must suddenly change in 

 intensity, unless oligoclase is entirely different from the other substances 

 examined ; for, like the others, in the oxyhydrogen flame, it emits an intense 



