DICKE, Robert H. R. Beringer, R. L. Kyhl, and A. B. Vane,  “Atmospheric Absorption Measurements with a Microwave Radiometer”, in Physical Review, volume 70/5+6, September 1 and 15, 1946.   In the original wrappers,  fine copy. $250

•  See: Henry Stroke, The Physical Review, the First Hundred Years, 1995, reproduced in full in the Gravity Physics and Cosmology section, pp 497-505.  See also John Boslough and John Mather The Very First Light: The True Inside Story of the Scientific Journey Back to the Light at the dawn of the Universe.
  

  “In 1946, Robert Dicke and coworkers at MIT tested equipment that could test a cosmic microwave background of intensity corresponding to about 20K in the microwave region. However, they did not refer to such a background, but only to ‘radiation from cosmic matter’. Also, this work was unrelated to cosmology and is only mentioned because it suggests that by 1950, detection of the background radiation might have been technically possible, and also because of Dicke’s later role in the discovery”.– Kragh, H. (1999). Cosmology and Controversy: The Historical Development of Two Theories of the Universe.