De charactere geometrico principali formarum crystallinarum octaedricarum pyramidalibus rectis basi rectangula oblonga commentatio.
(21 x 18 cm). (2) 28 S. Halbleinwandband um 1920.
Leipzig, Tauchnitz, 1809.
Einzige Ausgabe eines seiner beiden Hauptwerke. - "Very rare. In this thesis, which continues ideas expressed in the 'De Indagando Formarvm Crystallinarvm' of the same year, Weiss emphasized the importance of direction in crystals, attributing their formation and rationality of crystal faces to a generating force that is directional in nature. Crystallographic axes had a physical significance and could therefore be used as the foundation of a system of crystal classification. Weiss proposed to classify crystals into four main systems, with subdivisions, by considering crystallographic axes mutually perpendicular to one another. He begins by dividing crystals into two principal categories. The first division consists of crystals with three axes, each perpendicular to the other two. Three possibilities were noted to occur in this division: 1) the lengths of all axes were equal, 2) the lengths of two axes were equal, while the third was either shorter or longer, and 3) the lengths or all three axes were different. By this means Weiss distinguished the present isometric, tetragonal, and orthorhombic crystal systems. The second major division Weiss noted consists of three equally spaced axes at right angles to a fourth axis. Currently, this is recognized as the hexagonal or trigonal crystal system" (Schuh). - Weiss (1780-1856), Schüler von Werner, war Professor für Mineralogie in Berlin und Direktor des mineralogischen Museums ebendort. - Mehrfach gestempelt. Erstes und letztes Blatt gestempelt, sonst gut erhalten. - DSB 14, 239; Poggendorff II, 1287. - Sehr selten