Doc Ewen: The Horn, HI, and Other Events in US Radio Astronomy

Slide 28: Detecting the Interstellar Hydrogen Line, 1951

Letter from Joseph Pawsey to Ed Purcell, April 20, 1951. Frank Kerr, teaching at Harvard while on leave from CSIRO Division of Radiophysics, had written to Pawsey of the detection. At Purcell's suggestion, I went to the Harvard Observatory, in mid April, to meet and talk to Van de Hulst for the first time, and to tell him about the discovery. Ed told me that Van de Hulst was teaching a course at Harvard during the spring term. It was the same course that he taught at Leiden, during the prior fall term. When I met with Van de Hulst at the Observatory he called Oort, and I talked with Oort for nearly an hour describing the switch frequency technique. This was the first time that we learned the Dutch had been searching for the line for several years. Had we known, we would not have tried. [Photo courtesy of Doc Ewen]
Slides 29-30