Ångström, Anders Jonas

(b. Lödö, Medelpad, Sweden, 13 August 1814; d. Uppsala, Sweden, 21 June 1874)

astronomy, physics.

Ångström was the second son of Johan Ångström, a minister. He attended elementary and secondary schools in Härnösand, then began his studies in mathematics and physics at the University of Uppsala in 1833. In 1839 he received a docotorate with a dissertation on the optics of conical refraction, and then became a lecturer in physics at Uppsala. He went to Stockholm Observatory in 1842 in order to gain experience in practical astronomy, and the following year he was appointed assistant professor of astronomy at Uppsala Observatory. He was professor of physics at Uppsala from 1858 until his death. His most important physical papers are those on spectroscopy, but he also wrote on terrestrial magnetism and the conduction of heat.

In February 1853 Ångström presented his “Optiska undersökninger” (“Optical Researches”) before the Stockholm Academy of Science. In this work, he observed that the spectum of an alloy of two metals contained the spectrum of each of the constiuent metals and that an eletric spark yielded two superimposed spectra, one from the metal of the electrodes and the other from the gas through which it passed. He also compared terrestrial emission spectra with the dark lines of the solar spectrum and concluded that a terrestrial specturm was essentially a reversal of a portion of the solar spectrum. Proceeding from Euler’s resonance theory, Ångström deduced that an incandescent gas should emit spectral lines of the same wavelenghts as those it absorbed, thus proposing a relationship between the emission and absorption spectra of a chemical element that was more fully and effectively presented by Gustav Robert Kirchhoff several years later. This work establishes Ångström as one of several significant predecessors of Kirchhoff in formulating the foundations of modern spectroscopy.

After 1861 Ångström intensively studied the spectrum of the sun, noting the presence of hydrogen in the solar atmosphere and confirming the probable existence there of a number of other elements. In 1868 he published his monumental Recherches sur le spectre solaire, which contained an atlas of the solar spectrum with measurements of the wavelenghts of approximately a thousand lines determined by the use of diffraction gratings. Ångström expressed his results in units of one ten-millionth of a millimeter—a unit of length that has been named the angstrom unit in his honor.

In order to have a precise basis for the new science of spectroscopy, accepted standards were needed. In 1816 Kirchhoff made a map of the solar spectrum and labeled lines with the corresponding scale readings of his own prismatic instrument. These rapidly became the almost universally accepted manner of designating spectral lines, but they were inconvenient because each observer had to correlate his own readings with those of the arbitrary Kirchhoff scale Ångström’s wavelength measurements provided a more precise and convenient reference and, after 1868, became a competing authoritative standard. Unfortunately, as was noted later, the length of the Uppsala meter was not 999.81 millimeters, the value used by Ångström, but 999.94 millimeters. Eventually Ångström’s scale was replaced as the accepted standard by the more precise tables published by Henry Augustus Rowland between 1887 and 1893.

In 1867 Ängström was the first to examine the spectrum of the aurora borealis. A work on the spectra of the metalliods, which was begun some years previously, was completed by Tobias Robert Thealén, who actively assisted Ångström for many years, and was published in 1875. In opposition to the view that a given chemical element had a multiplicity of spectra, depending upon conditions, Ångström remained a strong defender of the opinion that each chemical element had a single characteristic spectrum that remained essentially unchanged.

Ångström’s scientific merit was widely recognized. He twice shared the Wallmarsh Prize of the Royal Academy of Stockholm, and in 1872 he was awarded the Rumford Medal of the Royal Society of London. He was a member of scientific societies in Uppsala, Stockholm, Copenhagen, Berlin, Paris, and London, among others. Late in Ångström’s life, his scientific work had to compete with various administrative duties . He was secretary of the Uppsala Scientific Society (1867–1874), a member of the Uppsala Scientific Council of the city of Uppsala (1868–1873), and served the university as president of the Council of Economic Administration (1869–1874) and rector (1870–1871).

BIBLIOGRAPHY

I. Original Works. Ångström’s two most important spectral publications are “Optiska undersökningar,” in Philospohical Magazine, 9 (1855), 327–342; and Recherches sur le spectre solaire (Uppsala, 1868). Other articles of significance are “On the Fraunhofer Lines Visible in the Solar Spectrum,” in Philosophical Magazine, 24 (1862), 1–11; “New Method of Determining the Thermal Conductivity of Bodies,” ibid., 25 (1863), 130–142; “On the of the Aurora Borealis,” ibid., 38 (1869), 246–247; “On the Spectra of the Simple Gases,” ibid., 42 (1871), 395–399; and, with T. R. Thaléen, “Recherches sur les spectres des metalloïdes,” in Nova acta Societatis Regiae scientiarum upsaliensis, 9 (1875), article 9.

II Secondary Literature. A short biography of value is that by Anna Beckman in Swedish Men of Science 1650–1950, edited by Sten Lindroth and translated from the Swedish by Burnett Anderson (Stockholm, 1952), pp. 193–203. Two contemporary unsigned biographical obituaries are in Nature, 10 (10 September 1874), 376–377; and Proceedings of the Royal Society of London, 25 (1877), xviii-xxii.

C. L. Maier