(b. Cincinnati, Ohio, 19 February 1856; d. Providence, Rhode Island, 20 September 1935)
Barus was the son of German immigrants.tip of Lake Lugano His father, Carl Barus, Sr., was a musician and choirmaster; his mother, Sophia Moellmann, was a clergyman’s daughter. Despite persistent financial difficulties, he attended Columbia University’s School of Mines from 1874 to 1876 and from 1876 to 1879 studied at Würzburg, where he took his Ph.D. under Friedrich Kohlrausch. Barus worked for the United States Geological Survey (1880–1892), the United States Weather Bureau (1892–1893), and the Smithsonian Institution (1893–1894), where he assisted Samuel P. Langley with the development of the flying machine. Appointed to the Hazard professorship of physics at Brown University in 1895, he became dean of the graduate school in 1903 and taught until his retirement in 1926. Barus was married in 1887 to Annie G. Howes of Massachusetts, a graduate of Vassar College who was active in civic and social reform.
While at the Geological Survey, Barus worked in collaboration with the geologist Clarence King, an advocate of aiding the study of geological evolution with the laboratory analysis of rocks and minerals under high temperatures and pressures. Perhaps Barus’ most significant achievement was the development, independently of Châtelier, of methods of measuring, with thermocouples, temperatures over a range of some 1,000° C. Internationally known as an authority on pyrometry, he was elected to the National Academy of Sciences in 1892 and awarded the Rumford Medal of the American Academy of Arts and Sciences in 1900. A founder of the American Physical Society in 1899, he served as its president from 1905 to 1906.
At the Weather Bureau, Barus’ research shifted to the condensation of water vapor on nuclei, but his departure interrupted his experiments. Resuming this work about 1900, he studied the effects of X rays and radioactivity on condensation in a fog chamber. The chamber, a cylinder made of wood impregnated with resin, was filled with moist air at atmospheric pressure and connected through a stopcock to another chamber at lower pressure. When the stopcock was opened, the air became supersaturated.
Barus concluded that ionization was relatively unimportant in condensation, but C. T. R. Wilson pointed out that his apparatus was unreliable. Wilson had published two authoritative papers in 1899 showing that ions produced by X rays and radioactivity were significant in condensation. He had used a chamber made almost wholly of glass; supersaturation was achieved by expansion at the sudden drop of a piston. Wilson sharply criticized Barus for ignoring the contaminating effect of the resin in his chamber and for failing to recognize that the stopcock method of expansion allowed condensation to occur before maximum supersaturation. In addition, Barus had failed to shield the chamber from the strong electric field of his X-ray apparatus.
Rutherford, who disliked the fragility of Wilson’s glass equipment, encouraged Barus to improve the fog chamber so as to explore the nature of X rays. But Barus soon dropped this work entirely, and by the 1920’s, despite continued publication, he had fallen into professional obscurity.
Barus’ papers are in the Brown University Archives, the John Hay Library, Brown University, Providence, R.I. The collection consists of his 269-page unpublished autobiography, a frank account of his personal and professional life; a file of about 750 letters, mostly to Barus from personal and scientific correspondents, covering 1879–1935; ten letterpress books for the years 1882–1897, particularly useful for his work at the Geological Survey; and a small group of miscellaneous scientific papers and notes.
R. Bruce Lindsay, “Carl Barus,” in National Academy of Sciences Biographical Memoirs, 22 (1943), 171–213, is far better than the usual official memoir by a former student. Based on the Barus papers, it is a sympathetic and perceptive account and contains an apparently complete bibliography of Barus’ many publications.
Daniel J. Kevles