438 DOCUMENT 377 MARCH 1912 geht, auch dass Marie ein Bübchen (?) bekommt, von dem ich übrigens ja im- merhin so eine Art Onkel bin. Vero will ich ein kleines Buch mit Anleitung zu schönen Versuchen senden. Du musst Ihm aber etwas dazu helfen. Seid herzlich gegrüsst von Euerm Albert. [...] ALSX. [7 066]. The year is provided by the reference to Einstein's paper. See Einstein 1912d (Vol. 4, Doc. 4), submitted six days earlier (see Doc. 375). The fol- lowing summarizes this paper and the preceding one, Einstein 1912c (Vol. 4, Doc. 3). Most of the equations cited below are also in Einstein's "Scratch Notebook" (Vol. 3, Appendix A), [pp. 38-39]. See also the editorial note, "Einstein on Gravitation and Relativity: The Static Field," for a discussion. Should be "Weg." Einstein 1912c, 1912d (Vol. 4, Docs. 3 and 4) both appeared in the Annalen der Physik on 23 May. See Doc. 343, note 3, for more on the difference of opinion between Einstein and Max Abraham. Einstein 1912b (Vol. 4, Doc. 2) appeared the same day this letter was written. See Vol. 4, the editorial note, "Einstein on the Law of Photochemical Equivalence," for a discussion of the paper. Einstein's earlier remarks to Besso on this topic are in Docs. 331 and 354. He had with- drawn a paper on the subject two months earlier (see Doc. 343). See Doc. 313, note 7, and Doc. 344, note 5, for more details. Einstein visited Berlin the third week of April (see Doc. 384). Walther Nernst, Max Planck, Heinrich Rubens, Emil Warburg, Fritz Haber, and Erwin Freundlich. Nernst had published a proof of his heat theorem that was contested by Einstein. See Doc. 364, note 6, for more background, and Doc. 366 for information on Nernst's reaction. Paul Habicht had gilded parts of the "Maschinchen" to prevent contact electricity. See the editorial note, "Einstein's 'Maschinchen' for the Measurement of Small Quantities of Elec- tricity," pp. 51-55. The "Auerstrumpf" or Welsbach mantle, named after Carl Auer von Wels- bach (1858-1929), was a very successful and widely used gas mantle. Habicht apparently concluded that radon gas evaporating from the mantle of a gas lamp in the vicinity of the "Maschinchen" was responsible for spurious ionization. On 9 March 1912 Paul Habicht delivered a lecture to the Schweizerische Physikalische Gesellschaft on the "Maschinchen" (see Habicht, P. 1912). Einstein was to begin a teaching appointment in Zurich in the autumn (see Doc. 341, note 1). Marie Müller-Winteler gave birth to Paul Albert Müller on 8 August 1912. Einstein's reference to himself as "a kind of uncle" is based on the fact that his sister Maja was married to Müller-Winteler's brother, Paul . The book intended for Vero Besso was probably Neuburger 1911, an experimental phys- ics primer, which Einstein mentions in his "Scratch Notebook" (Vol. 3, Appendix A), [p. 57]: "Experimental Physics Book of Delights Albert Neuburger" ("Erg. Exper. Buch Albert Neu- burger"). A postscript by Mileva Einstein-Marid is omitted.