WENTZEL PATH-INTEGRALS

Quantum mechanics can be arrived at in three ways, as Heisenberg, Schr odinger, and Feynman did, respectively. For the last way, an unknown ( i.e., forgotten) forerunner exists, which we have found in two papers by Gregor Wentzel, published before the famous works by Heisenberg and Schrodinger, and contemporary with the fundamental works of L. de Bro glie. In those papers, one can find the basic interpretation of the ac tion integral as a phase together with the concept of interference of all virtual paths-not only the classical solutions-and the interpretat ion of the result of the interference as the amplitude of a transition probability, both given by Feynman 20 years later, following Dirac.