American atmospheric physicist who applied basic physical laws to explain the optical, electrical, acoustical, and thermal properties and phenomena of the atmosphere.

Humphreys received his Ph.D. from Johns Hopkins University and, in 1905, after holding a number of teaching and research positions, began the affiliation with the U.S. Weather Bureau that lasted until his death. Much of his work, and indeed most of classical physical meteorology, is summarized in his Physics of the Air (1920).