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

Slide 23: Detecting the Interstellar Hydrogen Line, 1951

A fortuitous event: Report cover of Bill Mumford's gas discharge noise source for noise temperature calibration of the hydrogen line receiver, June 1949. [A Broad-Band Microwave Noise Source, by W.W. Mumford. Bell Telephone System Monograph 1721, also published in Bell System Technical Journal vol. 28, p. 601-618, 1949.] [Photo courtesy of Doc Ewen]
Slide 24