Cristallography

Towards 1801 Weiss made the hypothesis in his " law of zones" of the directional character of the crystal growth. He defined the crystal axes and explain how the crystal outer shapes are produced.

Bernhardi introduced circa 1801the concept of crystallographic system and defined 6 systems.

Mohs circa 1820 gave a rigorous definition of the 7 crystal systems by introducing the monoclinic and triclinic systems. (Mohs scale).

Delafosse , circa 1840, introduced the concept of division in unit cells of the crystal lattice.

J.F.C. Hessel (circa 1830) and Auguste Bravais (1811 - 1863) are the authors of the hypothesis of the reticular structure of the crystals (= postulate of Bravais), established the existence of 32 groups of symmetry of reticular network. Bravais published in 1849 his " Crystallographic studies ".