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In their seminal review of physics research around 1900 [1], Forman, Heilbron and Weart observed that “men of independent means with private laboratories, and the occasional engineer or industrial physicist with the time and taste for basic research” remained an exception at a time when physics research was a well-established academic discipline1. This was particularly true for Germany, where the 1905 directory [2] compiling active researchers in physics, mathematics and astronomy counted only few men under the elusive category of “Privatgelehrte”2 in physics. While this list includes eminent scientists such as Berend Wilhelm Feddersen (1832–1918) or Richard Zsigmondy (1865–1929), the case of a self-taught amateur who succeeded in contributing significant scientific achievements in physics was unusual at this time. The history of Viktor Schumann's (1841–1913) contributions to UV spectroscopy is a case study for progress off the beaten track in basic physics research at the turn of the 20th century. This contribution traces the work of a lone scientist, whose impact, incidentally, was first valorized abroad rather than in his home country.

Trading engineering for spectroscopic research

  1. Top of page
  2. Trading engineering for spectroscopic research
  3. Schumann's contribution to UV spectroscopy
  4. Knowledge transfer from Schumann to Lyman
  5. Acknowledgments
  6. References

Viktor Schumann was born in 1841 in Markranstädt near Leipzig [3]. He initially trained as a mechanical craftsman in Rothenburg an der Saale and later studied engineering in Chemnitz. After several years of work as a marker, Schumann became technical director of a company located in Leipzig where he worked from 1872 to 1893. Though successful in his work, Schumann had to suffer from several hardships in his private life. His son died as a young boy, and his wife passed away after seven years of marriage in 1878. Only a few weeks after this tragedy, possibly as a distraction from his sorrow, Schumann started to conduct private research on photography. From then on he spent the majority of his leisure time on photochemical and spectroscopic experimentation in his home laboratory. The knowledge that was necessary to conduct this work was acquired entirely from the self-study of scientific literature and the exchange of letters with other researchers. Yet, through improvements of the sensitivity of silver bromide gelatin photographic plates, Schumann was recognized by the academic peers in photochemistry, among them Josef Maria Eder (1855–1944) who included Schumann's protocols and results in his own reviews [4]. The analysis of the spectral sensitivity of photographic plates, which he conducted with a prism spectrograph from 1882 on, led him to gradually shift his interest from photochemistry to spectroscopy in the ultraviolet domain. His success in the photographic research community as well as his preoccupation with spectroscopy motivated Schumann in 1893 to quit his job as an engineer in order to devote himself entirely to his private research on the new field of vacuum spectroscopy which he pioneered, surviving on modest savings that he had made from his work. Health problems, in particular an unspecified nervous affection, forced him in 1895 to temporarily interrupt research, eventually stopping experimentation entirely in 1903. Schumann died on September 1st 1913 at the age of 71 years. Today, his work is not well known anymore, and the “Schumann rays”3, as the far ultraviolet radiation was first called, have disappeared from the literature. Obituaries for Schumann were written by the prominent physicists Otto Wiener [5] (1862–1927) and Theodore Lyman [6] (1874–1953). His instrumentation was highlighted in an exhibition at Deutsches Museum in 1936 for the commemoration of the 250th anniversary of the death of Otto von Guericke (1602–1686), setting his vacuum spectrograph as an exhibit in one line with the x-ray spectrograph of Nobel prize winner Manne Siegbahn [7]. During the time of National Socialism in Germany, Schumann's life was idealized as a selfless sacrifice to science, exploited for teaching the history of physics in Germany [8].

Schumann's contribution to UV spectroscopy

  1. Top of page
  2. Trading engineering for spectroscopic research
  3. Schumann's contribution to UV spectroscopy
  4. Knowledge transfer from Schumann to Lyman
  5. Acknowledgments
  6. References

At the beginning of the 19th century William Herschel (1738–1822) studied radiation in the previously unknown infrared [9] and, inspired by Herschel's results, Johann Wilhelm Ritter (1776–1810) observed the photochemical action of an ultraviolet part of the prismatic spectrum4. The name ultraviolet was introduced first by William Herschel's son John Herschel (1792–1871) in 1840 [10]. In 1852 George Stokes (1819–1903) drew the absorption lines in sunlight in the UV spectrum (Fig. 1) on a white screen covered with quinine sulfate [11]. He noticed that below 340 nm the missing part of the spectrum was essentially due to the absorption of glass. When calcite or fluorite optics was applied instead, the spectrum could be followed to even shorter wavelengths. The limit established by Stokes in the spectrum of aluminum spark discharges was set at 185 nm. From 1870 to 1890, no significant progress was made to enlarge the spectrum below the Stokes limit. Still, UV-spectroscopy attracted a lot of interest in the spectroscopy community as the wealth of UV-lines in the spectra of artificial light sources and their potential for the characterization of chemical elements had been recognized.

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Figure 1. Overview on classification schemes for the ultraviolet spectrum.

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Alfred Cornu (1841–1902) in 1879 suggested that a terrestrial atmospheric absorber must be at the origin of the cutoff in the observed solar spectrum below 300 nm [12]. A transcript of Cornu's work can be found in Viktor Schumann's early scientific diaries5. These reports stimulated him to reduce the influence of air on spectroscopic measurements, and to eventually construct a spectrograph operating under vacuum conditions. By using calcium fluorite optics the absorption limit of quarz could be overcome, and a new area of the spectrum up to 125 nm was analyzed. As the dispersion properties of calcium fluorite in UV were unknown at the time, Schumann could only estimate the location of the lines he had measured through extrapolation. The limit he had reached was, contrary to his belief of having measured lines up to 100 nm, around 125 nm, i.e., as it was shown later by Theodore Lyman at Harvard University, the transmission limit of calcium fluorite. It was Lyman who overcame this limit from 1906 on [13] through the construction of vacuum spectrographs using gratings instead of prisms, reaching a limit wavelength of 50 nm and thus in 1914 being able to discover the first series of the hydrogen spectrum that became an important confirmation of Bohr's atomic theory. Since 1919, Robert Millikan (1868–1953) and coworkers improved measurements of ionized atoms to below 20 nm [14]. The connection to the spectroscopy of soft x-rays was made through the crystal-diffraction experiments of Manne Siegbahn (1886–1978) and his scientific school [15].

Knowledge transfer from Schumann to Lyman

  1. Top of page
  2. Trading engineering for spectroscopic research
  3. Schumann's contribution to UV spectroscopy
  4. Knowledge transfer from Schumann to Lyman
  5. Acknowledgments
  6. References

Taking into account his unusual biography, it may seem surprising at first sight that Schumann as a single amateur could establish a new field at a time when spectroscopy was already an important field of academic research. Looking more closely at the three major requirements for the study of UV below 185 nm – i.e., i) the construction of a vacuum chamber to reduce the absorption through the air, ii) the fabrication of UV-sensitive photographic plates, iii) the use of calcium fluorite optics – it becomes apparent that Schumann, as a lateral entrant to physics research, had a unique combination of expertise in mechanical craftsmanship, in photochemistry, and in spectroscopy, which consequently enabled him to develop his instrumentation and experimental setup autonomously (Fig. 2). His new type of a low-concentration photosensitive emulsion that could be used for UV spectroscopy became a de facto standard in spectroscopic research for many years. Even though his experimental protocol and instrumentation had been published since 1893 with a very high level of descriptive detail [16, 17], the high requirements led to the situation that for many years no other academic researcher could reproduce or enlarge the knowledge Schumann had established. In 1910 Schumann retrospectively analyzed the situation and the lack of research in the field in a letter to Theodore Lyman:

“[…] I think it would happen more often if there wouldn't be two significant obstacles in the way: first, since most of the time the required vacuum spectrograph is missing, and second, since most physicists are not willing to deal with the fabrication of the necessary photographic plates since this is inconvenient and cumbersome to them. […]6

image

Figure 2. Comparison of the ultraviolet sensitivity of photographic plates by Viktor Schumann (undated before 1895); Deutsches Museum Archives.

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Requests for lending his instruments to other scientist were rejected. The experimental handling of the apparatus was in no way comparable to the experimentation with previous spectrographs, owing to the requirements of vacuum. Since Schumann was afraid of sleeping in foreign rooms, he almost never left Leipzig. As a consequence, anyone who was willing to learn from him had to visit him in his private laboratory.

That the transfer and transformation of knowledge was finally achieved by a young American scientist, and not by an established spectroscopist in Germany or England, can be attributed to Schumann's personal and financial ties to US institutions and scientists. Some of the 200 correspondents with whom Schumann frequently exchanged letter were located in America. He was able to read letters in English language, his replies, however, were always written in German. He obtained a part of his gratings and additional optical equipment from the workshops of John Brashear (1840–1920), who was working as an instrument maker for Henry Rowland (1848–1901). The astronomer George Hale (1868–1938), who had visited Leipzig, offered to Schumann a position in Chicago [17]. Schumann twice received 500 Dollars from the Hodgkins Fund of the Smithsonian Institution, enabling him to buy additional material for his research. In a letter from 1901 to the American sinologist and Smithsonian Institution curator Romyn Hitchcock (1851–1923), who had visited Schumann in Leipzig [18], Schumann stated:

“As my liquid funds are not large, I have to operate very economically if I want to dedicate myself to my studies without any cuts. (In our German empire one does not have liquid funds available for people of my type. For us it is not like in America, where the scientific endeavor of the private researcher is supported as much as that of a professional scientist.)”7

The alluded lack of support for amateur scientists in Germany, however, was not exactly true in his case. From 1902 onwards, Schumann received financial support from the Mende fund in Leipzig, and was promised to receive three rooms in the newly-built physics institute of the university. Ernst Mach (1838–1916) personally ensured that the assignment for the 1898 Baumgartner-Prize, devoted to contributions „to the extension of our knowledge on the behavior of the extreme ultraviolet radiation“ [19], could only be met by Schumann. He failed to apply due to health problems, and the prize was given to Pieter Zeeman (1865–1943) for his study of the change of spectroscopic lines in electromagnetic fields. When offered a position at the Grunewald observatory in 1895, Schumann rejected, noting in his diary that he was not inclined to give up his independence.

Theodore Lyman, who in 1902 was conducting research as a guest in Göttingen and who visited Schumann in Leipzig, also contributed financially to Schumann's research by a transfer of 500 Dollars. While, at first, he might have seen Lyman as a competitor, his perspective changed after recognizing the successful repetition and outperformance of his original experiments. A friendship evolved from the exchange between the two scientists, with over twenty letters sent between 1901 and 1913. Lyman had himself learned all the necessary requirements to perform the experiments and provided an essential improvement to the instrument through the introduction of gratings. To Schumann, Lyman was a worthy successor in this area of research, as he also recognized that Lyman's results helped to increase the popularity of his own work, and to become known as the pioneer of vacuum spectroscopy in the far-ultraviolet domain not only in America but also in his home country.

Acknowledgments

  1. Top of page
  2. Trading engineering for spectroscopic research
  3. Schumann's contribution to UV spectroscopy
  4. Knowledge transfer from Schumann to Lyman
  5. Acknowledgments
  6. References

I would like to thank Christian Joas, Klaus Hentschel, Julia Bloemer and Guido Fuchs for fruitful comments and discussions.

  1. 1

    For a study of the subdiscipline of astrophysics see [21]

  2. 2

    Approximate English translation “private scholar”

  3. 3

    see. e.g. in [22]

  4. 4

    For a recent discussion of Ritter's work see [23] for an overview of discussions on classification of radiation see [24]

  5. 5

    Most of Schumann's papers are archived at Universitätsbibliothek Leipzig (Nachlass 208–211).

  6. 6

    Original text: “Ich glaube, es geschaehe öfter, wenn Beobachtungen dieser Art nicht zwei wesentliche Hindernisse im Wege staenden: einmal, weil es allenthalben an dem erforderlichen Vacuumspectrographen fehlt, und zweitens, weil sich die meisten Physiker mit der Herstellung der erforderlichen photographischen Platten nicht befassen wollen da diese ihnen zu unbequem und zu umstaendlich ist.”

  7. 7

    Original text: “Da meine baarmittel nicht umfangreich sind, so muss ich sehr sparsam wirthschaften, wenn ich mich ungeschmaelert meinem Studium soll widmen können. (In unserem deutschen Reiche hat man für Arbeiten von Leuten meines Schlages keine baarmittel disponibel. Bei uns ist es nicht wie in Amerika, wo die wissenschaftlichen Bestrebungen des privaten Forschers ebenso unterstützt werden wie die des Berufsgelehrten.”

References

  1. Top of page
  2. Trading engineering for spectroscopic research
  3. Schumann's contribution to UV spectroscopy
  4. Knowledge transfer from Schumann to Lyman
  5. Acknowledgments
  6. References
  • 1
    P. Forman, J. L. Heilbron, S. Weart, Historical Studies in the Physical Sciences 5, 1185 (1975)
  • 2
    F. Strobel, Adreßbuch der lebenden Physiker, Mathematiker und Astronomen des In- und Auslandes und der technischen Hilfskräfte; Verlag Ambrosius Barth, Leipzig (1905)
  • 3
    F. Fraunberger, in: Dictionary of Scientific Bibliography 12, 235236 (1975)
  • 4
    J. M. Eder: Ausführliches Handbuch der Photographie; Verlag Knapp, Halle (from 1884 on)
  • 5
    O. Wiener, BVKSGW 65, 409427 (1913)
  • 6
    T. Lyman, Astrophys. J. 39(1), 14 (1914)
  • 7
    F. Fuchs, Guericke-Ausstellung; Deutsches Museum München 42 (1936)
  • 8
    Ä. Bäumer-Schleinkofer; in C. Meinel, P. Voswinckel (edts.): Medizin, Naturwissenschaft, Technik und Nationalsozialismus; GNT Verlag, Stuttgart 282294 (1994)
  • 9
    W. Herschel, Phil. Trans. R. Soc. Lond. 90, 284292 (1800); see also K. Hentschel: Mapping the spectrum; Oxford University Press (2002).
  • 10
    J. F. W. Herschel, Phil. Trans. Roy. Soc. London 130, 20 (1840)
  • 11
    G. G. Stokes, Phil. Trans. Roy. Soc. London 142, 463561 (1852)
  • 12
    A. Cornu, C. R. Acad. Sci. Paris 88, 11011108 (1879)
  • 13
    T. Lyman, Astrophys. J. 23(3), 181210 (1906)
  • 14
    R. A. Millikan, Ira S. Bowen, Phys. Rev. 23, 134 (1924)
  • 15
    M. Siegbahn, Spektroskopie der Röntgenstrahlen; Springer, Berlin (1924)
  • 16
    V. Schumann, SBAWW 102(2), 415475 (1893)
  • 17
    V. Schumann; SBAWW 102(2), 625694 (1893)
  • 18
    Henry Crew Collection, Northwestern University; 1895 diary
  • 19
    R. Hitchcock, Science 20, 160161 (1892)
  • 20
    E. Mach, SSBAW 105(3), 187188 (1896)
  • 21
    J. Lankford, Social Studies of Science 11(3) pp. 275303 (1981)
  • 22
    W. Ritz, Zur Theorie der Serienspektren; Phil. Diss. Göttingen (1903)
  • 23
    J. Frercks, H. Weber, G. Wiesenfeld, Studies in the History and Philosophy of Science 40(2), 143156 (2009)
  • 24
    K. Hentschel, Unsichtbares Licht? Dunkle Wärme? Chemische Strahlen? GNT-Verlag, Stuttgart, (2007).