Werner Heisenberg mechanics formulation of quantum mechanics. On 1 May 1926, Heisenberg began his appointment as a university lecturer and assistant to Bohr in Copenhagen. It was in Copenhagen, in 1927, that Heisenberg developed his uncertainty principle, while working on the mathematical foundations of quantum mechanics. On 23 February, Heisenberg wrote a letter to fellow physicist Wolfgang Pauli, in which he first described his new principle. In his paper on the principle, Heisenberg used the word ""Ungenauigkeit"" (imprecision), not uncertainty, to describe it. In 1927, Heisenberg was appointed "ordentlicher Professor" (professor ordinarius) of theoretical physics and head of the department of physics
Institute of Physics when the expansion of access to universities removed demand. In 1960, the Physical Society and the Institute of Physics merged, creating a single organization with the unwieldy name "The Institute of Physics and the Physical Society", which combined the learned society tradition of the Physical Society with the professional body tradition of the Institute of Physics. Under the leadership of Thomas E. Nevin an Irish branch of the Institute of Physics was formed in 1964. Upon being granted a royal charter in 1970, the organization was renamed as the Institute of Physics. There are four grades of membership: Associate Member,