Absorption Bands in the Infra-Red Spectrum of Venus

In 1922 St. John and Nicholson investigated the spectrum of Venus by photographing with a plane-grating spectrograph regions near A59OO, the a-band of oxygen near X6300, and the B-band of oxygen at A6867. The radial velocity of the planet and the dispersion employed were sufficient to separate planetary lines from those of terrestrial origin. No trace was found of lines due to oxygen or to water vapor in the spectrum of the planet. Recent progress at the Research Laboratory of the Eastman Kodak Company in sensitizing photographic plates to the infrared has made it possible to extend this investigation to the region of longer wave-lengths where the A-band of oxygen at 17594 and the group of strong water-vapor lines in the interval X8150A8300 afford excellent material for a sensitive test of the presence of molecules of these gases in the atmosphere of Venus. For this purpose we have used a plane-grating auto-collimating spectrograph, nine feet in focal length, at the coude focus of the 100inch reflector. The photographs, which cover the region X7400A8800, were taken in the first order of the grating and have a linear scale of about 5.6 A.U. to the millimeter. The exposure times were from two to four hours. Our observations were made in April and May when the planet was near greatest eastern elongation. The radial velocity of Venus relative to the Earth for the average date of observation was about 14 kilometers per second, which at A8000 corresponds to a displacement of 0.37 A.U. Since this represents a shift of 0.066 millimeters on our spectrograms, lines due to the planet would be separated clearly from terrestrial lines. The quantitative study of the spectrograms has not as yet been completed, but it is clear from inspection and microphotometer tracings that no lines of measurable intensity due either to oxygen