PHYSICS: BRINSMADE AND KEMBLE 
423 
Discussion. — According to the theory previously referred to,^ the in- 
fra-red absorption spectrum of a diatomic gas at moderate temperatures 
should consist of a relatively strong fundamental doublet accompanied 
by a faint harmonic. The latter band should also be a doublet and the 
wavelength difference of the components should be one fourth of the 
wavelength difference of the components of the fundamental. The 
theory applies to five gases, viz., CO, NO, HCl, HBr, and HI. Of these 
we have examined three, and in each case the prediction of the theory 
has been verified. The only discrepancy between theory and obser- 
vation consists in a sHght excess in the observed wavelengths of the 
'harmonics' over their computed values, amounting to 0.043 /x, 0.026iu, 
and 0.025 ix, in the cases of CO, HBr, and HCl respectively. 
II 
' HCl lutidam^rdai _ 1 i 1 
f ' FmII ime S«it> i-i w.d? ] f ""1 
f ||> DaJifd Jioe^Shti -''I 4_l 
pfc 
Biiif 
mm 
i 
M : 1 , 
'I H" 
fit 
[ 0 20r 400 
{s i: '!b . i]^ : ;'ij3^ 
€00 600 
1000 l?00 1 
100 1600 mo ' 2000 ' 2aDD ' ^4i9<j'"'f? 
FIG. 
This disagreement may be attributed to a slight error in the dispersion 
curves on which the wavelength measurements are based. As no absorp- 
tion bands other than those here mentioned are known in the near infra- 
red spectra of the gases investigated, it seems out of the question that 
the occurrence of these weak bands at wavelengths so near the computed 
values can be a matter of chance. Moreover, as these diatomic molecules 
have but one vibrational degree of freedom, it would be difficult to ex- 
plain the occurrence of two absorption bands in the iufra-red spectra 
of these gases except as the result of the non-simple harmonic character 
of motion of the two atoms along their line of centers. That the faint 
bands are not due to impurities is proved by the spacing of the maxima 
