Dirac, Paul A. M. (1902-84). Classical theory of radiating electrons. Offprint from Proceedings of the Royal Society of London, A, 167 (August 1938). 8vo (257 x 172 mm). Original printed wrappers, vertically creased, slight soiling. Provenance: Gregor Wentzel (1898-1978), physicist (name in pencil (erased) on the front wrapper; 8-page manuscript (in German) in Wentzel's hand commenting on Dirac's paper laid in). First Edition, Offprint Issue. '[Dirac's] paper of 1938 was an important contribution to electron theory and is still considered to be a classic' (Kragh, Dirac: A Scientific Biography, p. 189). In an attempt to resolve the issues with infinities that plagued quantum electrodynamics in the 1930s, Dirac set out to come up with a better classical theory of the electron that could then be quantized. In the present paper he created a finite theory of point electrons that yielded the 'Lorentz-Dirac' equation (also known as the 'Abraham-Lorentz-Dirac equation of motion'), which 'was exact and involved neither infinities nor structure-dependent terms' (Kragh, p. 194). Unfortunately, Dirac's theory, 'in spite of its formal beauty, . . . involved unphysical 'runaway' solutions (spontaneously accelerating electrons) that could be eliminated (at the classical level) only at the price of making supraluminal [faster than the speed of light] signals possible' (Dictionary of Scientific Biography). Dirac continued to work on classical electron theories until the 1960s. This important association copy is from the library of German physicist Gregor Wentzel, whose notable contributions to quantum mechanics include the Wentzel-Kramers-Brillouin approximation for finding approximate solutions to linear differential equations with spatially varying coefficients. In a three-part paper on the intrinsic forces of elementary particles ('Über die Eigenkräfte der Elementarteilchen'), published in 1933-34, Wentzel had introduced the lambda-limiting technique, which Dirac used in the present paper to eliminate infinities for a single electron up to the order of e2. As Dirac told Bohr in a letter written on 5 December 1938, 'the limiting procedure is effectively the same as Wentzel's, but it is now put into exact Hamiltonian form' (quoted in Kragh, p. 195). The manuscript laid into this copy, headed 'Dirac, August-Heft PRS,' is filled with Wentzel's commentary and equations; it includes a reference to Wentzel's own paper ('NB: Ergebnis = meinem von 1933' [NB: Result = mine from 1933]). For further information on this lot please visit Bonhams.com For further information about this lot please visit the lot listing