German mineralogist and physicist Franz Ernst Neumann died #OTD in 1895.
Neumann made significant advances in the mathematical understanding of crystal structures & their physical properties. His work laid the groundwork for the field of crystallography. He also developed the concept of the piezoelectric effect in crystals.In 1831, he established the Neumann's Law: the molecular heat of a compound is equal to the sum of the atomic heats of its constituents.