WEISS, CHRISTIAN SAMUEL

(b. Leipzig, Germany, 26 February 1780; d. Eger, Hungary, 1 October 1856), crystallography, mineralogy.

Weiss’s grandfather and father were archdeacons of Nicolai Church. At the age of twelve he began a classical education at the liberal Evangelische Gnadenschule at Hirschberg (now Jelenia Gora, Poland), under the philologist C. L. Bauer. In 1796 he returned to Leipzig to study medicine at the university; but after receiving his baccalaureate degree he switched to chemistry and physics, in which he was awarded the doctorate in 1800, and was then admitted to the faculty. Before teaching, Weiss spent two years in the chemical laboratory of Martin Klaproth (and Valentin Rose the younger) at Berlin, then a center for quantitative mineral analysis. Here he also became acquainted with Dietrich Karsten, curator of the royal mineral collection, and the eminent geologist Leopold von Buch. At their urging he went to the Freiberg Bergakademie for a year with A. G. Werner.

In 1805-1806 Weiss toured areas of geological interest in Austria, Switzerland, and France, spending some months in Paris with René-Just Haüy, André Brochant de Villiers, and Claude Berthollet. From 1803 he taught chedmistry, physics, and mineralogy at Leipzig, and in 1808 he was appointed professor of physics, At about that time the University of Berlin was being organized under Wilhelm von Humboldt’s leadership with the intention to make it the major center of philosophy and science in Germany by assembling the most eminent faculty. At Buch’s instigation Weiss was appointed to the professorship of mineralogy and Klaproth to one on chemistry. Classes at the new university began in 1810, and Weiss occupied the chair of mineralogy until his death. After Dietrich Karsten’s death in 1810, Weiss also became curator of the mineralogical museum and was instrumental in getting the government to purchase Buch’s priceless collections for the museum in 1853. He served as rector of the university in 1832-1833.

Weiss’s ability as a teacher was attested to by generations of students, several of whom made major contributions in science: Gustav Rose, Karl Rammelsberg, Friedrich Quenstedt, Adolph de Kupffer, and particularly Franz Neumann.

In addition to his major contributions to crystallography, Weiss published a number of papers in geology; and with Alexander von Humboldt and Buch he helped lay Werner’s neptunist theories to rest.

While he was still a young man, Weiss’s many contacts put him at the very center of the quickly developing science of crystallography. At Karsten’s suggestion, he early embarked on a translation of Haüy’s Traité de minéralogie, to which he added lengthy supplements on the process of crystallization. His intimate acquaintance with Werner’s very practical view on mineralogy was an effective antidote to Haüy’s imaginative but often unsubstantiated speculations. He had high regard for both men, but he did not show either of them the uncritical devotion that each asked of his followers.

Weiss’s interpretations of the geometry of crystals were first indicated in his inaugural dissertation for the professorship at Leipzig (1809). They were developed in a long series of papers published in the Abhandlungen, der Königlichen Akademie der Wissenschaften in Berlin (he was elected a member of the academy in 1815) and in publications of the Gesellschaft Naturforschender Freunde in Berlin. He never published his own textbook of crystallography, alough those of Quenstedt (Tübingen, 1840; 1855; 1873) are perhaps derived from his work. His contributions to crystallography were early shaped around the directional aspect of crystals, which he regared in an abstract, theoretical way as the expression of processes of growth. Hanüy’s theories of crystallography, then preeminent, interpreted crystals in terms of cleacage-shaped “molecules,” which had to be combined in various steps to explain the varieties of crystal forms. By 1815 Weiss had developed the idea of crystallographic axes, which were at once a direction of growth and a basis of classification. In this most important contribution Weiss distinguished crystal systems by the way in

which faces were related to such axes: first by whether they resulted in axial intercepts of equal lenght, and second by whether all or only a fraction of a set of related faces (modern “form”) were developed by crystals of a given mineral species.

In the second of these criteria Weiss incidentally provided the first recognition of hemihedrism²— that is, a crystal class or point group that displays lower symmetry with a fraction of the faces, while retaining the smae basic symmetry or crystal system. It should be clear, however, that while Weiss and others before him implicitly recognized the main rotational axes of symmertry, as well as miror plances of symmetry, the classification was essentially metrical; and the complete symmetrical classification of crystals into both the seven crystal systems and Hessel’s thirty-two crystal classes or point groups(1830) was not completed unit 1849 by Auguste Bravais. As shown in the table, we can read into Weiss’s listing the crystal systems that are now the primary classification of crystals; but two fundamental faults of Weiss’s crystallography continued to be a source of confusion and debate for the next decade or so. First, Weiss insisted on choosing crystallographic axes at right angles, describing as hemihedrisms of the orthorhombic system the crystals now recognized as separate monoclinic and triclinic systems. Second, the axial lengths, while recognized as being unequal in each system except the cubic, were nevertheless thought to have ratios related by square roots of integers.

These two assertions were made plausible by the marked pseudosymmetries of many minerals of low symmetry, such as feldspar. But they were soon disproved by the accurate measurements of interfacial angles made by Kupffer and others using William Wollaston’s optical goniometer, by Neumann’s demonstration of the variation of angles with temperature, and by Eilhard Mitscherlich’s demonstration of the variation of angles in a series of solid solutions. Much of this work had been done at the University of Berlin in Weiss’s laboratory and that of his colleague Gustav Rose. But throughout his life Weiss insisted on perpendicular “rational” axes, while increasingly precise measurements pushed him to justify his position with calculations such as an axial ratio for gypsum³

Weiss’s philosophical emphasis on important directions in crystals resulted not only in the crystallographic axes and crystal systems but also, even earlier, in the concept of the zone. Although originally conceived as a direction of prominent crystal growth, the term soon was formally defined as the collection of crystal faces parallel to a single line, the zonal direction. The zone concept enabled Weiss to propose replacing Haüy’s symbolism for crystal faces with parameters that described the face direction in terms of its intercepts in units of his crystallographic axes. The Weiss symbols were widely used, and eventually they were replaced by the reciprocal sysmbols known today as Miller (although earlier used by Carl Naumann) indices. Weiss’s last important contribution (1820) was the development of algebraic relations among the paramters (e.g., Weiss or Miller indices) of the faces that constitute a zone—Weiss’s zone law—which remains a powerful tool in crystallographic calculations. Its application was greatly simplified by Franz Neumann, using projections, in his Beiträge zur Kristallonomie (Berlin-Posen, 1823).

From his earliest years Weiss’s development as a scientist was strongly influenced by contemporary philosophers, and notably by the theories of nature of Immanuel Kant, Friedrich Schelling, and Johann Fichte—much to the dismay of his clerical father. Weiss was a keen observer but constitutionally disinclined to any experimental work, preferring to base his developments on abstract concepts of mathematical order—to the extent that where experiment was in disagreement, he chose to believe the more orderly theory. It is perhaps ironic that his student Franz Neumann went on to form at Königsberg the most important school of experimental physics (including crystal physics) of the nineteenth century. But Weiss’s contributions— crystallographic axes, crystal systems, the zone law, and the concept of hemihedrism—constructed a formal edifice in which much of nineteenth-century crystallography found a compatible home and a place to grow.

NOTES

1. “Uebersichtliche Darstellung…der Kristallisations-systeme,” table, 336 f. Friedrich Mohs independently worked out an analogous arrangement of crystal systems (but correctly, with inclined axes for the monoclinic and triclinic systems), published in his Grundriss der Mineralogie, 2 vols. (Dresden, 1822-1824). David Brewster had already seen the MS of William Haidinger’s English trans. of this work— Treatise on Mineralogy, 3 vols. (Edinburgh, 1825)—and immediately applied the crystal systems to the interpretation of his observations on double refraction of crystals. A polemical debate on priority ensued in the Edinburgh Philosophical Journal, 8 (1823), 103–110 (Weiss) and 275–290 (Mohs). It is an interesting commentary on scientific communications of the day that although Weiss’s paper was read at the Berlin Academy of Sciences on 14 Dec. 1815, the Abhandlungen for that year was not printed until 1818; and at the end of 1822 a copy was still not in the library of the Bergakademie at Freiberg.

2. Weiss soon recognized other hemihedrisms in the tetragonal and hexagonal systems—see his paper in Edinburgh Phitosophical Journal, 8 (1823), 103–110.

3. “Über das Gypssystem,” in Abhandlungen der Königlichen Akademie der Wissenschaften in Berlin (1834), 623–647.

BIBLIOGRAPHY

I. Original Works. Most of Weiss’s scientific writings are listed in the Royal Society Catalogue of Scientific Publications, IV. 308–310. The most important books are De indagando formarum crystallinarum charactere geometrico principali (Leipzig, 1809), trans. into French with commentary by André Brochant de Villiers in Journal des mines, 29 (1811), 349–391, 401–444; and De charactere geometrico principali formarum crystallinarumoctaedricarum pyramidibus rectis basirectangula oblonga commentatio (Leipzig, (1809).

Articles include “Uebersichtliche Darstellung der verschiedenen natürlichen Abteilung der Krystallisations-systeme,” in Abhandlungen der Königlichen Akademie der Wissenschaften in Berlin (1814-1815), 289–344; “Ueber ein verbesserte Methode für die Bezeichnung der vershiedenen Flächen eines Krystallisations-systeme, nebst Bemerkungen über den Zustand von Polarisirung der Seiten in der Linien der krystallinischer Struktur.” ibid. (1816-1817). 286–314; and “Ueber mehrere neobeobachtete Krystallflachen des Feldspathes und die Theorie seines Krystallsystems im Allgemeninen,” ibid. (1820-1821). 145–184.

His translation of Haüy is of primary importance for the original commentaries by Weiss: R. J. Haüy, Lehrbuch der Mineralogie, 4 vols., trans. by K. J. B. Karsten and C. S. Weiss (Paris-Leipzig. 1804-1810).

Some of Weiss’s teaching materials are preserved at the Deutsche Staatsbibliothek, Berlin, D.D.R.; see Peter schmidt. “Zur Gexchichte der Geologie, Mineralogie und Paläontologie,” in Veroffentliclumger, der Bibliothek der bergakademie Freiberg, no. 40 (1970). items 675. 807. A large collection of Weiss’s letters to his oldest brother. Benjamin. are at the University of Marburg: they were used by both Groth and Fischer in preparing their discussions of Weiss.

II. Secondary Literature. Biographical notices of Weiss are by K. F. P. von Martius, in Akademisc Denkreden …von Martius (Leipzig, 1866). 327–344: and in Martin Websky et al., Gedenkworte am Tage der Feier des hundertijahrigen Geburtstages von Christian Samuel Weiss den 3 März 1880 (n.p., n.d.). A contemporary evaluation of Weiss’s crystallography is in Franz von Kobell. Geschichte der Mineralogie von 1650-1860 (Munich, 1864), 202–214. The most useful and modern critical discussions of Weiss’s scientific contributions are paul Groth. Entwicklungsgescbichte der mineralogischen Wissenschaften (Berlin, 1926: repr. Wiesbaden, 1970). 59–76: and Emil Fischer, “Christian Samuel weiss und seine Bedeutung für die Entwicklung der Krystallographie,” in Wissenschaftliche Zeitschrift der Humboldt-Universitäl zu Berlin, Math-naturwiss. ser. 11 (1962), 249–255. See also Fischer’s “Christian Samuel Weiss und die zeitgenössische Philosophie (Fichte, Schellig),” in Forschungen und Fortschritte, 37 (1963), 141–143. A more general evaluation of Weiss’s influence in the development of crystallography is J. G. Burke. Origins of the Science of Crystals (Berkeley, 1966), 147–164.

The founding of the University of Berlin. in which Weiss had a part, is described by Rudolf Virchow in “The Founding of the Berlin University and the Transition From the Philosophic to the Scientific Age,” in Anjual Report of the Board of Regents of the Smithsonian Institution (1894), pt. 1, 681–695.

William T. Holser