Georg Wolfgang Krafft (16.07.1701-16.07.1754) was a German physicist. He was born in Titlingen. He graduated from the University of Tübingen. In 1725 — 44 he worked at the St Petersburg Academy of Sciences (academician from 1727), in 1731 he was appointed professor of mathematics and physics, and in 1733 he took the chair of theoretical and experimental physics and became head of the physics cabinet of the Academy. In 1731—44 he was secretary of the Academy. In 1744 he returned to Germany, where he was professor at the University of Tübingen.
His work concerned hydrodynamics, heat, thermometry, optics, acoustics and magnetism. He carried out research to determine the refractive index and the density of ice and some of its other properties, and he measured the force of attraction of magnets. He worked on improving various physical instruments, in particular thermometers and barometers. He was the first in Russia to begin experiments in calorimetry. He was the first to propose (1744) an empirical formula for the temperature of a mixture of hot and cold water.
Krafft's services in putting in order and enlarging the physics cabinet of the St Petersburg Academy of Sciences were considerable. He succeeded in adding a large number of apparatus and instruments to the cabinet and in equipping a physics lecture room for the demonstration of experiments. Thanks to Krafft's efforts the Academy's physics cabinet became one of the best in Europe. He wrote a number of scientific and popular-science articles and books; in particular he delivered the first complete course of lectures on physics and wrote (1738) the first physics textbook for students. He did much to popularise the heliocentric system of the world.