Radio Observations of the Interstellar OH Line at 1,667 Mc/s

THE first experimental evidence for the presence of 18-cm absorption lines of the hydroxyl (OH) radical in the radio absorption spectrum of Cassiopeia A , as suggested by Lilley 1 , was obtained by Weinreb et al. 2 based on observations made during the period October 15–29, 1963. The Radio Physics Laboratory, Commonwealth Scientific and Industrial Research Organization, in Sydney, Australia, has reported the successful measurement of OH absorption in the spectrum of Sagittarius (see preceding communication).