AEPINUS, FRANZ MARIA ULRICH THEODOR HOCH

born Dec. 13, 1724, Rostock, Mecklenberg-Schwerin died Aug. 10, 1802, Dorpat, Russia physicist whose Tentamen theoriae electricitatis et magnetismi (1759; "An Attempt at a Theory of Electricity and Magnetism") was the first work to apply mathematics to the theory of electricity and magnetism. Aepinus studied medicine before turning to physics and mathematics. His work in these new fields resulted in his election to the Berlin Academy of Sciences and, in 1757, led to a professorship of physics in St. Petersburg. He remained in St. Petersburg until his retirement in 1798. Aepinus' experiments led to the design of the parallel-plate capacitor, a device used to store energy in an electric field. He also discovered the electric properties of the mineral tourmaline and investigated pyroelectricity, the state of electrical polarization produced in tourmaline and various other crystals by a change of temperature. In addition, Aepinus studied the relation between conductors and nonconductors, extended Benjamin Franklin's one-fluid theory of electricity, and explained virtually all electric induction in terms of the attraction, repulsion, and flow of electricity in conductors. Aepinus improved the microscope, and his essay on the effects of parallax in the transit of a planet across the Sun's disk excited great general interest, for it was published in 1764, between the dates of two transits of Venus.