422 DOCUMENT 366 FEBRUARY 1912 While attending the Solvay Congress in Brussels Einstein had found a thermodynamic proof for the law of photochemical equivalence (a paper on this topic was received by the An- nalen der Physik on 18 January 1912 see Einstein 1912b [Vol. 4, Doc. 2]) and enlisted Emil Warburg's support for its experimental verification (see Doc. 308). See Warburg 1912 for his experimental results on the ozonization of oxygen that confirmed Einstein's theory. See also Vol. 4, the editorial note, "Einstein on the Law of Photochemical Equivalence." See Doc. 343, note 3, for more on the controversy between Max Abraham and Einstein. H. A. Lorentz had inquired two weeks earlier about Einstein's interest in assuming his duties at the University of Leyden (see Doc. 359). Einstein accepted a position as Professor of Theoretical Physics at the ETH on 12 Febru- ary (see Doc. 358). He expressed his dismay at the thought of succeeding to the Leyden chair a few days later (Doc. 360). Peter Debye. Einstein was unsure whether Debye would remain in Zurich, where he had recently been promoted (see Doc. 344). Debye had also been appointed Professor of Mathematical Physics and Theoretical Mechanics at the University of Utrecht on 3 February (see Doc. 344, note 3) but had only conditionally accepted (see Peter Debye to Curatoren, 11 February 1912, NeUR, Archief College van Curatoren Rijksuniversiteit Utrecht, 637). After agreement had been reached on his salary, Debye officially accepted on 18 March (see Peter Debye to Curatoren, 18 March 1912, NeUR, Archief College van Curatoren Rijksuniversiteit Utrecht, 637) and he withdrew from the University of Zurich at the end of that month (see Peter Debye to Erzie- hungsdirektion, Canton of Zurich, 28 March 1912, SzZSa, U 110 b .2 (48)). Paul Ehrenfest had inquired about a position in Zurich earlier in the month (see Doc. 357, note 1). Einstein argues here that countries less tolerant than Switzerland would not confer an academic appointment on Ehrenfest because of his refusal to register a religious af- filiation. While visiting Prague Ehrenfest repeatedly asserted his unwillingness to do so in or- der to obtain an appointment at the German University, though another significant motivation seems to have been his wish to accompany Einstein to Zurich at all costs (see Paul Ehrenfest to Tatiana Ehrenfest, 25 February and 28 February 1912, NeLR, Ehrenfest Archive, Personal Correspondence, EPC:3, sec. 6). Einstein, who was registered as without religious affiliation in Switzerland, had circumvented the issue a year earlier by registering as "Jewish" with the Austrian authorities (see Doc. 238, note 1). Einstein implicitly touches on a second issue in pointing out that Ehrenfest would not be likely to leave a position in Switzerland. The authorities of the University of Zurich had shown displeasure when Einstein left the university a year earlier (see Doc. 247, note 3) and would be similarly unhappy should Einstein's successor, Debye, also vacate the position. Alfred Kleiner's reaction was conveyed to Einstein by Ehrenfest, who was visiting Prague at the time and who had met with Kleiner in mid-February in Zurich. Even before his meeting with Kleiner, Ehrenfest was told by Debye of Kleiner's outright refusal to consider him for a Privatdozentur at the University of Zurich (see entry of 12 February 1912, Diary "D," NeLR, Ehrenfest Archive, Notebooks, ENB:4-10). The idea of dividing the functions of Debye's chair of theoretical physics into two-one intended by Einstein for the theoretician Ehrenfest, the other for an experimentalist-paral- leled the considerations of the authorities at the University of Zurich. Theoretical physics had become such a "comprehensive discipline" ("ausgedehntes Fach"), argued the Zurich Govern- ing Council in its decree appointing Debye's successor, that its practitioners should concen- trate fully on their specialty and be relieved of their obligation to participate actively in the area of experimental physics (see Aus dem Protokoll des Regierungsrates 1912, no. 1457, 18 July 1912, SzZSa, U 110 b .2 (50)). Mathilde Zangger-Mayenfisch and the youngest daughter, Gina.