Theodore Lyman was an American physicist, educator, and author. He was a professor in physics at Harvard University from 1917 to 1925.
Background
Lyman was born on November 23, 1874 in Brookline, Massachusetts, the son of Theodore Lyman, a marine biologist who served one term in Congress, and Elizabeth Russell Lyman. His great-grandfather was a Boston merchant whose wealth permitted his descendants to follow their inclinations without concern for earning a living.
Education
Lyman graduated from Harvard in 1897 and received the Doctor of Philosophy degree in physics in 1900. His early interest in mechanical things had led him to consider majoring in electrical engineering, and he worked at this field during his junior and senior years. However, Wallace Sabine's course in optics attracted him to that field. Sabine offered him the assistantship in physics, which he held for three years while completing his doctoral dissertation, "False Spectra from the Rowland Concave Grating" (1900). The lines of these false spectra appeared intermingled with true lines and were a source of trouble to experimenters. In his dissertation Lyman explained that these "Lyman ghosts" were due to periodic irregularities in the grating ruling. Later he continued his studies at Cambridge and Göttingen.
Lyman became an instructor at Harvard University, assistant professor in physics in 1907 and full professor in 1917. Four years later he received the Hollis professorship, the oldest endowed American scientific chair. After his retirement in 1925, he continued to give a course in optics until 1939 and directed doctoral work until 1942. He was director of the Jefferson Physical Laboratory from 1910 until 1947. It was alleged that, because of his wealth, he accepted no salary at Harvard.
Lyman's scientific work was in the area of the extreme ultraviolet. The spectrum of radiation transmitted through air is cut off at about 1, 850 angstroms by the absorption of the air. Shortly before Lyman began his work Viktor Schumann had extended the spectrum with an evacuated spectrograph to a limit set by the absorption of the fluorite optics (now known to be 1, 260 angstroms). Lyman substituted a concave grating to remove this absorption and to give lines evenly spaced according to wavelength. He thus made the first exact wavelength determinations by comparing the second-order spectrum of the unknown ultraviolet lines with the superposed first-order spectrum of known lines of twice the wavelength. By 1915 he had extended the known spectrum to 600 angstroms and, by 1917, to 500 angstroms. He identified the "Lyman" or fundamental series of hydrogen in the vacuum ultraviolet.
Lyman's work was interrupted from 1917 to 1919 by military service. He was sent to France in 1917 as captain in the Signal Corps to develop flash and sound ranging. He was soon placed in charge of a training school in this technique, and from April to November 1918 he commanded a flash ranging unit at the front, serving in three battles, including those on the Marne in June and July. He returned as a major with the Second Army in charge of a battalion of more than 1, 000. He considered this experience "one of the most interesting of my whole life. " Although Lyman felt that during the war others had taken over leadership in ultraviolet spectroscopy, he continued to work in the field and to study spectra down to 256 angstroms. His scientific productivity diminished after 1926 because of his duties at Harvard and ill health.
He was active in raising funds for a new research laboratory at Harvard, which was later named for him. In May 1930, while en route to England, he suffered a ruptured appendix, which required emergency surgery. The experience left him with a crippling phlebitis in one leg. He also suffered from failing eyesight, which he attributed to the strain of measuring spectra. He was thus obliged to have his experimental work performed by an assistant but continued to direct it. Much of his later study was devoted to the transmission in the extreme ultraviolet of various gases and to an unsuccessful attempt to improve the sensitivity of photographic plates in the ultraviolet. He contributed some valuable scientific papers to the literature. His last published paper (1935) dealt with the transparency of air between 1, 100 and 1, 300 angstroms.