I N T R O D U C T I O N T O V O L U M E 7 x x i x
roboration of his quantum theory of light. But it would soon become clear that Ein-
stein’s experiment did not have the implications he had hoped for: also according
to wave optics, no deflection was to be expected.
In 1921, Wander J. de Haas presented a paper on the Einstein–De Haas experi-
ment at the third Solvay Congress in Brussels. It contains a section by Einstein
(included in Appendix B) in which he generalizes his earlier derivation (in Einstein
and De Haas 1915a [Vol. 6, Doc. 13]) of the connection between angular momen-
tum and magnetic moment for a magnetized body.
With his increasing visibility and the expansion of his circle of colleagues,
acquaintances, and correspondents, Einstein received numerous requests and sug-
gestions for scientific diversions, his term for investigations that did not lie in the
mainstream of his scientific interests. To these belongs his suggestion in Einstein
1918i (Doc. 6), in response to the concern of radiologists, that total reflection may
account for strange shadows on the X-ray radiographs of patients’ limbs. Einstein
1920c (Doc. 39), on the determination of chemical reaction velocities in partly dis-
sociated gases by using the propagation of sound, did not elicit much attention at
the time, although later, molecular acoustics developed as a novel investigative tool
in physical chemistry. His paper fits with ongoing experiments at the time in the
laboratory of Walther Nernst, with whom he shared an interest in the thermody-
namics of chemical reactions and in a cooling process designed to patent and
develop a new refrigerator.
Einstein’s expertise in examining and criticizing patents had been honed two
decades earlier in the Swiss Patent Office. His involvement with patent work in the
period covered in this volume comes therefore as no surprise. Mostly it was friends
and acquaintances who solicited his assistance. His first expert opinions had been
rendered in patent disputes in 1914 (Vol. 6, Docs. 12, 19). In addition to further
opinions on behalf of Hermann Anschütz-Kaempfe (Docs. 11, 21) in 1918 and
1919, Einstein continued to deal with technical problems such as lightbulb filament
production (Doc. 30), radio transmission (Doc. 48), and sound detection (Doc. 67).
Einstein had long been hoping to see his gravitational theory put to a decisive
empirical test. It was clear to him that the best experiment available was an obser-
vation of light deflection during a solar eclipse. In his opinion, among contempo-
rary theorists only Gunnar Nordström had produced a serious competitor to his
general theory (see his remarks in Einstein 1913c [Vol. 4, Doc. 17, p. 1262]), but
he was convinced that eclipse results would decisively prove the superiority of his
own theory (Einstein to Michele Besso, ca. 10 March 1914 [Vol. 5, Doc. 514]).
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