Recent observations have placed a very narrow bound on the extent of the celestial x-ray source in the constellation Scorpio (hereinafter designated “Sco X-1”) and provoked a suggestion that it may represent a hitherto unseen class of objects, protostars. The observation, which placed a bound of 20 sec of arc on the angular diameter of Sco X-1, was made on 8 March with a rocket-borne experiment by Herbert Gursky, Riccardo Giacconi, Paul Gorenstein, John R. Waters of American Science and Engineering Corp.; Minoru Oda, Hale Bradt, Gordon Garmire and B. V. Sreekantan of MIT. It was published in the June issue of The Astrophysical Journal (144, 1249, 1966). The suggestion that Sco X-1 is a protostar is by Oscar P. Manley of American Science and Engineering and appeared in the same issue of The Astrophysical Journal as a companion letter to that of Gursky and his associates.