124 



INFRA-RED EMISSION SPECTRA. 



the reflecting power of the substance under examination. The maximum 

 reflection and the minimum emission do not coincide on account of the 

 high reflecting power on the side toward the long wave-lengths, which 

 suppresses the emission curve, thus shifting its minimum farther into the 

 infra-red. The only other example heretofore investigated is by Rosen- 

 thal, 1 for quartz, which will be described in the next chapter. The band 

 at 4.7 // is of interest since it occurs in CO and C0 2 in the vacuum tube 

 radiation (see Carnegie Publication No. 35), and is in common with the 

 carbonates and the sulphates. 



RELATION BETWEEN EMISSIVITY AND ENERGY CONSUMPTION. 



The substances just described must have one or both of two kinds of 

 spectral energy distribution, due (1) to the general absorption which is 

 present to some extent, however small, and which gives rise to a continuous 

 spectrum, and (2) to bands of selective absorption which give rise to 

 emission bands. 



The object in examining the isochromatic radiation curves of the 

 aforesaid solids is to determine whether or not the observed sharp emis- 

 sion bands behave like spectral lines, or like bands which include a con- 

 siderable portion of the spectrum. If the observed bands behave like 

 those of a gas, the emission must be proportional to the energy supplied. 



If the radiation is similar to 

 the complex and highly damped 

 emission of a solid, e.g. plati- 

 num, the isochromatics can not be 

 straight lines, but must be similar 

 j^2.42j /i tQ ^Qgg f platinum. 



A complete radiator emits 

 energy, however small the 

 amount, of all wave-lengths, 

 whatever its temperature above 

 the absolute zero. The isochro- 

 matic energy curves must, there- 

 fore, all begin at the origin of 

 the energy axis; and they may 

 have a double curvature. This 

 is well illustrated in fig. 93 for 

 the isochromatic radiation curve 

 of platinum at 2.752 p.. The 

 platinum strip was 50 by 1.5 by 0.02 mm., in an exhausted glass bulb, with 

 a fluorite window. In this figure the graphs of wave-lengths X= 1.804 P- an d 

 ^=1.968 11 intersect at 2.8 watts, showing that the maximum of the energy 

 curve lies between these two wave-lengths; temperature about 1100 C. 



12 3 4 5 Waits 



- Isochromatic radiation curves of platinum. 



1 Rosenthal: Ann. der Phys. (3), 68, p. 791, 1899. 



