SCHUMANN, VICTOR

(b. Markranstädt, near Leipzig, Germany, 21 December 1841; d. Leipzig, 1 September 1913)

photography.

Schumann is known among physicists as UV Schumann because of his development of photographic plates capable of registering ultraviolet light. The son of Karl Ferdinand Schumann, a physician, he attended the local elementary school and was then sent to a Realschule in Leipzig. Following a year of practical training in an engineering works, he studied mechanical engineering works, he studied mechanical engineering from 1861 to 1864 at the Royal Technical College at Chemnitz (now Karl-Marx-Stadt). In 1865 he was cofounder of an engineering works in Leipzig of which he served as technical director. Schumann was obliged to retire in 1893 because of overwork and damage to his eyes that appeared to be leading to blindness. His first wife, Auguste Baumgarten, daughter of a factory owner in Chemnitz, whom he married in 1871 after a youthful romance, died only seven years later. He remained a widower until 1909, when he married Elise Börner.

Schumann was an extremely successful engineer and designer, especially of machines for book production. It was, however, in photography that he won international recognition. Schumann took up photography as a hobby in 1872 and, after the death of his wife, spent all his limited leisure time on it. He became a member of the Berlin Photographic Society in 1882 (and later an honorary member), and in 1894 the University of Halle awarded him an honorary doctorate. During the last three years of his life he was also a full member of the Royal Saxon Academy of Sciences in Leipzig.

Schumann took up photography while it was still in its infancy. The necessity for long exposures was further complicated by the impossibility of representing various tints by different degrees of photographic density: a red or yellow object, for example, appeared as dark as a black one. Schumann found, however, that adding a small amount of silver iodide to the customary silver bromide emulsion not only permitted significantly shorter exposures, but also yielded markedly improved contrasts for red and yellow objects. This finding contradicted the publications of experts in England and on the Continent, who claimed that the addition of silver iodide produced still weaker contrasts. Accepting the challenge implicit in this disagreement, Schumann demonstrated that both sides were justified in their claims. The experts had prepared silver bromide and silver iodide emulsions separately and then mixed them, a technique that resulted in inferior plates. By reversing the procedure—dissolving the light-sensitive salts together in water and then adding the gelatin—Schumann produced plates that were far superior. Earlier, in 1873, he had increased sensitivity to red by allowing solutions of certain organic dyes to act on prepared plates. The announcement of this technique stimulated a wealth of further research by both amateurs and industry.

Schumann held that the most informative way of investigating the sensitivity of photographic plates to color was to expose them through a spectroscope. He was particularly interested in the ultraviolet region. As George Stokes had shown, this region could be made strikingly visible through a device in which the collector is formed by placing quartz lenses and calcite prisms on plates of fluorescent uranium glass. A problem remained, however: Why did shorter wavelengths of light darken the plates less than longer wavelengths? Schumann discovered two reasons for this. First, because the gelatin absorbed the light before it reached the silver bromide, he prepared plates in which these particles were not dispersed throughout the layer of gelatin but, rather, adhered to the top of it. Second, he established that the air in the spectrograph was highly disruptive, creating problems of both dispersion and, especially, absorption. Schumann discovered that a layer of air even 0.10 millimeter thick could completely absorb a spectral line.

Since no firm could furnish or build him a vacuum spectrograph, Schumann constructed one himself. The prisms and plates had to be adjusted precisely from outside the apparatus, and it took him a full year to devise an aperture that fulfilled his requirements. When finished, the device produced sharper spectra than any previously seen: with his plates it became possible to photograph spectra as low as 1,270 Å, whereas the limit had been 4,000 Å. (Theodore Lyman subsequently recorded spectra at 1,030 Å.) This further advance made it possible to demonstrate the Lyman series of hydrogen (predicted by J. J. Balmer), the first member of which lies at 1,215 Å. Since the majority of spectral lines of the elements lie in the ultraviolet region, the amateur photographer Schumann also became a pioneer of spectroscopy and of atomic physics.

BIBLIOGRAPHY

I. Original Works. Schumann’s writings include “Wirkung d. AgJ auf die Lichtempfindlichkeit d. AgBrGelatine,” in Photographisches Archiv (1882); “Über die Photographie der Lichtstrahlen kleinster Wellenlänge,” in Sitzungsberichte der Akademie der Wissenschaften in Wien, 102 , sec. 2a (1893), 415–475, 625–694; “Über ein neues Verfahren zur Herstellung ultraviolettempfindlicher platten,” ibid., 994–1024: “New Method of Preparing plates Sensitive to Ultraviolet Rays,” in Astrophysical Journal, 3 (1896), 220–226, 387–395: and 4 (1896), 144–154; and “Verbessertes Verfahren zur Herstellung ultraviolettempfindlicher Platten,” in Annalen der Physik, 4th ser., 5 (1901), 349–374. He also made many contributions to Jahrbuch für Photographie und Reproductionstechnik between 1887 and 1903.

II. Secondary Literature. Obituaries are T. Lyman, in Astrophysical Journal, 39 (1914), 1–4, withportrait; and O. Wiener, “Victor Schumann,” in Berichte über die Verhandlungen der Sächsischen Gesellschaft der Wissenschaften, 65 (1913), 409–413.

F. Fraunberger