246 DOCUMENT 211 JULY 1910 Ihre neue Abhandlung[9] macht mir ausserordentliche Freude. Wie können Sie denken, dass ich die Schönheit einer solchen Untersuchung nicht zu schätzen wüsste? Die Betrachtung der formalen Beziehungen in vier Dimen- sion erscheint mir als ein Fortschritt wie etwa die Einführung komplexer Funktionen in Hydrodynak & Elektrostatik zweier Dimensionen.[10] Ich habe mich wahrscheinlich Ihnen gegenüber in Salzburg hierüber unrichtig ausge- drückt.[11] Die Bedingungen des [Ge]schehens (Differenzialgleichungen) sind symmetrisch in vier Dimensionen diese Erkenntnis erleichtert das Auffinden jener Bedingungen. Die Grenze der Bedeutung der vierdimensionalen Be- trachtung scheint mir darin zu liegen, dass in den uns interessierenden Lösun- gen jener Gleichungen die vier Dimensionen nicht in gleicher Weise auftre- ten. P.S. Nach Prag komme ich nicht. Das Ministerium hat-wie ich aus Prag erfahre-Schwierigkeiten gemacht[12] AL (GyMDM, Sommerfeld-Nachlaß, Bopp/Hoffmann subcollection). Eckert and Pricha 1984, p. 33. [70 156]. The signature and a section of the letter preceding it are cut out. There are perforations for a loose-leaf binder at the left margin of the document. [1]Summer semester 1910 at the University of Zurich ended 5 August (see Zürich Verzeich- nis 1910a, title page) and winter semester 1910/1911 began 17 October (see Zürich Verzeichnis 1910b, title page). Sommerfeld visited Zurich at the end of August (see Doc. 223). [2]See Lorentz 1910a (which was actually published in Physikalische Zeitschrift) and Planck 1910b. In his paper Lorentz expresses his skepticism as to the existence of light quanta, using arguments (concerning the small number of quanta required to make an impression on the retina and the spatial dimensions of a light quantum) that he had earlier advanced in his correspondence with Einstein (see Doc. 153). Planck stresses the need to introduce quanta in the theory of radiation in "as conservative a manner as possible" ("so konservatif als mög- lich"). He suggests refraining from modifying Maxwell's equations but instead treating the en- ergy of an oscillator as a multiple of hv (at least while it is being excited). [3]A year earlier Einstein was still involved in a lively correspondence with Planck (see Doc. 172). [4]The assumption used in Einstein's theory of specific heats (see Einstein 1907a [Vol. 2, Doc. 38]). [5]Nernst 1910, which is referred to in Einstein's "Scratch Notebook" (Vol. 3, Appendix A), [p. 26]: "Nernst Berl. Berichte 1910 S 262-282." See also Doc. 199, note 9, for more on the experimental confirmations by Nernst and others of Einstein's theory of specific heats. [6]The experiments were performed by Otto Reinkober (1884-1947) and were published as Reinkober 1911, which summarizes his 1910 doctoral dissertation. The published results show no evidence of an absorption peak at 12|i. The theoretical prediction of 11|X was made in Ein- stein 1907a (Vol. 2, Doc. 38), p. 389. [7]See Ladenburg, R. 1909 for a contemporary review of experiments on the photoelectric effect. [8]Swiss German for "geschickte Lösung." [9]Sommerfeld 1910b, the first of two papers in which Sommerfeld developed a four-dimen- sional formalism for special relativity. The sequel is Sommerfeld 1910c. [10]Earlier Einstein had avoided the use of a four-dimensional formalism (see Doc. 101, note 12). [11]At the 81st meeting of the Gesellschaft Deutscher Naturforscher und Ärzte in September of the previous year.