An all-reflecting telescope and spectrometer have been employed in conjunction with a Cashman PbS cell to secure a direct-intensity map of the solar spectrum in the region of 0.8-2.5 ~i with a resolution of about 50,000. Four molecular-band systems at 1.66, 2.20, 2.32, and 2.37 ~ have been identified as the P1 + V4~ V3 + P4 and ~2 + P3 transitions of CH4 in the earth's atmosphere. A preliminary analysis of the wave numbers of the 2P3 rotational components indicates second-order deviations from theory. The average half-spacing B0 is found to be 5.163, as compared with the value B0 = 5.252 obtained by Childs. A comparison of the 2P3 telluric line intensities with those produced by a measured quantity of methane at room temperature leads to a calculated methane abundance in the earth's atmosphere of 1.2 parts in a million by mass, and a temperature of -37° C
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McMath et al. (1949) studied this question.