422 
PHYSICS: BRINSMADE AND KEMBLE 
absorption curve obtained. When this curve was taken the spectro- 
meter was not properly adjusted to give its full resolving power. How- 
ever, it is easy to see that the band is actually a doublet and that within 
the limits of error of our observations the separation of the maxima of 
the components is that predicted. The vertical lines a-a in the figure 
have the wavelength separation predicted for the maxima from Bur- 
meister's observations on the fundamental. On the other hand, the 
wavelength of the center of the band is greater than it should be by 
0.043 fjL, 
This band had previously been observed by Coblentz, Burmeister, 
and others, but had not been resolved into its two components. 
Eydrohromic Acid. — Burmeister gives only one absorption band in 
the infra-red absorption spectrum of HBr, viz., a doublet with maxima, 
(corrected for slit-width by the Paschen-Runge formula) at 4.013 m and 
3.836 ju. The center of the harmonic should be at 1.962 /x and the sepa- 
ration of the maxima should be 0.0442 ju. Figure 2 shows the absorption 
curve obtained. The widths of the entrance slit and thermopile slit 
are indicated by two pairs of short vertical lines marked E. S. and T. S. 
respectively. The distance between the maxima is in satisfactory agree- 
ment with the theoretical distance (cf. vertical lines a-a). As in the 
case of CO the wavelength of the center of the band is greater than that 
expected, the error being 0.026 /x- 
Hydrochloric Acid. — The infra-red absorption spectrum of HCl con- 
sists, according to Burmeister, of a single doublet with maxima (cor- 
rected for slit-width) at 3.394 ^ and 3.557 m- We have found an addi- 
tional doublet (fig. 3) with maxima at 1.783 ^l and 1.742 /z. As in the 
cases of the other gases examined the observed wavelength of the center 
of the band is somewhat greater than it should be if the band is a true 
harmonic of the one at 3.475 but the separation of the maxima agrees 
with the theoretical value predicted from Burmeister's observations. 
Figure 4 shows this same HCl band as observed with narrower slits. 
The quantum lines discovered by v. Bahr in the fundamental are re- 
solved on the long wavelength side of the band but not on the short 
wavelength side. The reason for the asymmetry in the positions of 
the quantum lines will be discussed below. 
Figure 5 shows the fundamental as observed when the tube was 
filled with a mixture of air and HCl, the latter having a partial pressure 
of 20.3 cm. The absolute magnitudes of the absorption shown by this 
curve have not been determined as accurately as we hope to determine 
them in the future, but the positions of the bands are probably to be 
relied on. The wavelength of the center of this band is less than that 
observed by Burmeister with a prism by 0.01 m- 
