ST.JOHN, CHARLES EDWARD

(b. Allen, Michigan, 15 March 1857; d. Pasadena, California, 26 April 1935)

astronomy.

The youngest in the family of Hiram Abiff St. John, a millwright, and Lois Amanda Bacon, St. John graduated from the Michigan Normal School in 1876. Overwork had weakened his health, however, and he could not resume work until 1885, when he became an instructor of physics at the normal school. He received the B.S. degree from Michigan Agricultural College in 1887; and after graduate study at the University of Michigan and at Harvard, including also a stay in Berlin and Heidelberg, he was awarded the Ph.D. by Harvard in 1896. After a year as an instructor at the University of Michigan, St. John was appointed associate professor of physics and astronomy at Oberlin College, becoming professor in 1899 and dean of the College of Arts and Sciences in 1906. Beginning in 1898, he spent several summer vacations working at the Yerkes Observatory. His association there with George Ellery Hale led him, in 1908, to resign his post at Oberlin and to join the staff of the Mount Wilson Observatory; after his retirement in 1930 he was appointed a research associate there.

St. John’s research was mainly in solar physics. One of his earliest investigations (1910–1911) was of the H and K lines of ionized calcium in the solar spectrum. After measuring the absolute wavelengths of these lines in terrestrial sources, he compared them with those of the corresponding emission and absorption lines observed in the solar spectrum, making a particular study of the spectral lines over sunspots and flocculi. In 1913 St. John confirmed John Evershed’s discovery concerning the displacement of Fraunhofer lines in the spectra of the penumbras of sunspots, and he made a detailed examination of the flow of gases in the spots. He concluded that ionized calcium exists at the highest level in the solar atmosphere, followed by hydrogen, with the metals and rare elements confined to the lower regions; his analysis of the flash spectrum obtained by S. A. Mitchell during the 1905 eclipse reinforced this conclusion. At the same time St. John refuted W. H. Julius’ idea that the displacements in the spectral lines were due to anomalous dispersion in the solar atmosphere.

St. John’s principal contribution was his revision of Rowland’s table of the wavelengths in the solar spectrum. In collaboration with Charlotte Moore, Louise Ware. Edward Adams, and Harold Babcock, he produced this monumental work in 1928. Two independent series of measurements were made, one with the Mount Wilson tower spectrographs and the other with an interferometer; the differences rarely exceeded 0.002 Å. From the violet limit of 2,975 Å, the lines listed ranged beyond Rowland’s extreme of 7,330 Å to about 10,200 Å. The revision listed the intensities of the spectral lines in spots as well as in the disk, and the lines were classified according to their furnace spectra and behavior under pressure; excitation potentials were also provided. In connection with this work St. John served for a time as president of the International Astronomical Union commission devoted to wavelength standards, and he was also president of the solar physics commission.

St. John paid particular attention to the problem of measuring the relativistic deflection of the lines in the solar spectrum. An initial study (1917), based on some forty lines, gave a negative result. By 1923, however, he was satisfied that the effect, which at the center of the sun amounts to about 0.01 Å, was detectable; and his final publication on the subject (1928), using 1,537 lines, illustrated it quite convincingly. Although St. John regarded this as his most important work, the motion of the perihelion of Mercury and the systematic displacement observed beyond the limb of the sun are generally regarded as more definitive tests of relativity.

In collaboration with Walter Adams and Seth Nicholoson, St. John made spectroscopic observations of Mars and Venus, mainly in the hope of detecting the presence of oxygen and water vapor in their atmospheres.

BIBLIOGRAPHY

I. Original Works. St. John’s Revision of Rowland’s Preliminary Table of Solar Spectrum Wavelengths, With an Extension to the Present Limit of the Infra-Red, written with C. E. Moore, L. M. Ware, E. F. Adams, and H. D. Babcock, is Carnegie Institution of Washington Publication no. 396 (Washington, D.C., 1928) and Papers of the Mount Wilson Solar Observatory, 3 (1928). Most of his other publications appeared in Astrophysical Journal and were reprinted as Contributions from the Mount Wilson Solar Observatory. They include “The Absolute Wave-Lengths of the H and K Lines of Calcium in Some Terrestrial Sources,” in Astrophysical Journal, 31 (1910), 143–156; “The General Circulation of the Mean and High-Level Calcium Vapor in the Solar Atmosphere,” ibid., 32 (1910), 36–82; “Motion and Condition of Calcium Vapor Over Sun-Spots and Other Special Regions,” ibid., 34 (1911), 57–78, 131–153, and 38 (1913), 341–391; “On the Distribution of the Elements in the Solar Atmosphere as Given by Flash Spectra,” ibid., 40 (1914), 356–376; “The Accuracy Obtainable in the Measured Separation of Close Solar Lines: Systematic Errors in the Rowland Table of Such Lines,” ibid., 44 (1916), 15–38, written with L. W. Ware; “The Elimination of Pole-Effect From the Source for Secondary Standards of Wave-Lengths,” ibid., 46 (1917), 138–166, written with H. D. Babcock; “On Systematic Displacements of Lines in Spectra of Venus,” ibid., 53 (1921), 380–391, written with S. B. Nicholson; “Evidence for the Gravitational Displacement of Lines in the Solar Spectrum Predicted by Einstein’s Theory,” ibid., 67 (1928), 195–239; “Elements Unidentified or Doubtful in the Sun: Suggested Observations,” ibid., 70 (1929), 160–174; and “Excitation Potential in Solar Phenomena,” ibid., 319–330.

II. Secondary Literature. Obituary notices appeared in Astrophysical Journal, 82 (1935), 273–283; Publications of the Astronomical Society of the Pacific, 47 (1935), 115–120; and Popular Astronomy, 43 (1935), 611–617. See also Walter S. Adams’ notice in Biographical Memoirs. National Academy of Sciences, 18, no. 12 (1938), 285–304, with bibliography of St. John’s works.

Brian G. Marsden