Prof. H. N. Russell

Abstract

PROF. H. N. RUSSELL, professor of astronomy at Princeton University, U.S.A., is one of the best-known American astronomers. He first became prominent through his theory of stellar evolution, according to which a star, contracting continuously throughout its history, passed successively through a ‘giant5 stage of rising, and a ‘dwarf state of falling, surface temperature. This theory, regarded somewhat sceptically at first, gained general acceptance through the discovery, by means of Adams and Kohlschutter's spectroscopic method for determining absolute magnitudes, of the reality of the distinction between giant and dwarf stars. The development of the theory of stellar constitution called for some amendment of the original postulates of Russell's theory, and it is characteristic of him that he made no attempt to preserve ideas based on insufficient data, but became a leader in the reformulation which was seen to be necessary. He was among the earliest to realize the importance of Saha's theory of ionization in stellar atmospheres, and took a leading part in working out its implications, always with a keen appreciation of the limitations placed on theoretical possibilities by difficulties inherent in methods of observation. The development of laboratory spectroscopy attracted him strongly, and with the collaboration of Prof. F. A. Saunders he obtained the first evidence of the co-operation of extra-nuclear electrons in producing line spectra: ‘Russell-Saunders coupling’ is now a well-established, and the most frequently occurring, type of such co-operation. More recently he has made important contributions to the analysis of complex spectra corresponding to various stages of ionization—particularly those of metals prominent in celestial spectra.