A Reader Answers: ‘Critical Mass’ Origin

Cameron Reed asked about the origin of the term “critical mass” (Physics Today, Physics Today 0031-9228 57 1 2004 14  https://doi.org/10.1063/1.1650054 January 2004, page 14 ). A search of the full text database of the NASA Astrophysics Data System (http://ads.harvard.edu) shows that “critical mass” was first mentioned in 1919, in volume 31 of the Publications of the Astronomical Society of the Pacific, page 121. An article by Hugo Benioff attributes the term to Arthur Eddington, who “singled out a critical mass—one at which a vital change of condition takes place.”