EINSTEIN, Albert (1879-1955). Autograph letter signed ("A. Einstein") to Johannes Stark, Bern, 13 April 1907.

In German. One page on a postcard, 140 x 90mm (lower left margin toned, two file holes, one of which affects one letter of text on verso). Addressed in his hand on verso together with his return address signed "A. Einstein" with a Bern postal cancellation (one file hole affects the second line of Einstein's return address).

Einstein compliments Johannes Stark's work utilizing the quantum hypothesis to explain the Doppler effect in light emitted by canal rays—the same physicist who would later seek to obliterate Einstein's influence over "German Physics" under the Nazis. He writes that he is pleased to hear that Stark will continue his work "on the emission of light and absorption of canal rays," and is looking forward to reading his forthcoming paper, "with the same great interest with which I studied your paper of last year." In December 1907, and again in 1908, Stark published additional data on his experiments, work that Einstein described as a "very important" application of quantum theory. (See AE to Joab Laub, 1 November 1908 Papers, 5, No. 125). Johannes Stark (1874-1957) was Dozent Professor of Practical Physics and Photography at the Technical University of Hanover and won the 1919 Nobel Prize in physics for his work on the Doppler effect. Stark was also an early supporter of Adolf Hitler and, with his fellow Nobel Laurate Philipp Lenard, spearheaded the Deutsche Physik movement that sought to purge Germany of the "Jewish Physics" of Albert Einstein and his supporters. Following the end of the Second World War, a denazification court found Stark to be a "major offender," and was sentenced to four years in prison. Ironically, Einstein and Stark share the "Stark-Einstein Law," also known as the photoequivalence law, that both discovered independently between 1908 and 1913. Published in Papers, Vol 5, No. 45. Provenance: M. B. Weisinger, New York.