SUMMARY. 131 



fact that, with rise in temperature, the C0 2 emission band shifts toward 

 that of CO, at 4.6 pt, and that eventually all three gases, C0 2 , CO, and O, 

 when radiating by electrical excitation in a vacuum-tube, have their im- 

 portant emission band in common at 4.75 n, it does not seem unreasonable 

 to assume that the latter maximum is due to the oxygen atom set free 

 during the time intervening between dissociation and recombination, 

 brought about by the electrical discharge in the carbon oxides. 



In a broad sense the intensity and sharpness of the emission bands 

 are a function of the electrical conductivity. The best insulators (strong 

 bases), e.g., the refractory silicates, the oxides of aluminium, zirconium, 

 erbium, etc., have the sharpest emission bands, while the best electrical 

 conductors, such as the oxides of cerium, iron, zinc, etc., have no sharp 

 emission bands. The molecular weight of the base seems to affect the 

 sharpness of the bands to as great an extent as does the electrical con- 

 ductivity, the sharpest bands occurring as a rule in oxides of low basic 

 molecular weight. These results, if true, are to be expected from our 

 knowledge of the emission, absorption, and reflection of electrical con- 

 ductors and insulators. 1 



Paschen, using the spectral energy curves of the oxides of iron and 

 copper, found no variation of the emissivity constant, a, with rise in tem- 

 perature. On the other hand, Lummer and Pringsheim, using the total 

 radiation from these substances, found that the emissivity increased with 

 rise in temperature. Such a change in emissivity is to be expected, for it 

 can be shown that at the highest temperatures the emissivity constant, a, 

 must decrease, otherwise a point would be reached where the emissivity 

 is greater than that of a complete radiator. In the present curves, where 

 sometimes at high temperatures the emission seems to be distributed into 

 apparently two bands, the "constant" a, derived from the spectral energy 

 curve of one band, may be different from that obtained from the total 

 radiation measurements. This is illustrated in the present study of the 

 Nernst glower, where Mendenhall and Ingersoll, 2 using total radiation, 

 found no certain variation in a with rise in temperature. 



From one line of theoretical consideration, one might expect to find, 

 with rise in temperature and the accompanying increase in the electrical 

 conductivity of the oxides, that the reflecting power increases. If this be 

 true, then the spectral emission ought to become more continuous, as is 

 found in the Nernst glower, and the emissivity constant, a, should retain 

 a high value similar to that of metallic electrical conductors. The value 

 of a from the spectral radiation curve was found to decrease with rise in 

 temperature, while Mendenhall and Ingersoll found no certain variation 

 in a, when measuring the total radiation. It is evident that experiments 



1 This subject has been thoroughly treated by Aschkinass: Ann. der Phys. (4), 17, p. 

 960, 1905. 



2 Mendenhall & Ingersoll: Phys. Rev., 24, p. 230, 1907; 25, p. i, 1907. 



