DOCUMENTS 147, 148 APRIL 1909 167 ALS (NeHR, Archief H. A. Lorentz). [16 413]. There are perforations for a loose-leaf binder at the head of the document. [1]Hendrik Antoon Lorentz was Professor of Theoretical Physics at the University of Leyden. [2]Einstein 1909b (Vol. 2, Doc. 56). [3]In §7 of Einstein 1909b (Vol. 2, Doc. 56) the fluctuations of the radiation-pressure are calculated with the help of Planck's law. The result turns out to be incompatible with a theory based on electrodynamics and molecular mechanics only. [4]James Jeans see Jeans 1905e for his derivation of the displacement law using dimension- al considerations. [5]In §10 of Einstein 1909b (Vol. 2, Doc. 56) Einstein uses a generalization of Jeans's ap- proach to derive a general form for the radiation formula, which includes both the Rayleigh- Jeans law and Planck's law and contains an unspecified scalar function. Comparison with Planck's law leads to the conclusion that Planck's constant h is determined by the quotient Ģ2/c (with e the elementary charge and c the speed of light), up to a numerical factor with the approximate value of 900. 147. To Johannes Stark Bern, 6 April 1909. Einstein expresses pleasure "that you have achieved an external position commensurate with your outstanding capacity for work. But I am also rather pleased that you hit upon the idea of choosing me to assist you, even if I am not in a position to accept your friendly offer. As I am married, the income from such a position would not be sufficient" ("daß Sie nun eine äußere Stellung erlangt haben, die Ihrer eminenten Arbeitskraft entspricht. Nicht wenig freut es mich aber auch, daß Sie darauf verfallen sind, mich zu Ihrem Mitarbeiter zu wählen, wenn ich auch nicht in der Lage bin, Ihr freundliches Anerbieten anzunehmen. Da ich verheiratet bin, wären die Einnahmen jener Stelle nicht groß genug"). Stark was appointed Professor of Experimental Physics at the Technical University of Aachen on 1 April (see Aachen Programm 1909, p. 166). Einstein's salary at the Swiss Patent Office was 4500 francs (see Doc. 34). Einstein sends him his "most recent paper, which is primarily critical, but also contains the reasons which cause me to ascribe a kind of molecular constitution to radiation" ("neueste Ar- beit, die hauptsächlich Kritisches enthält, aber auch die Gründe, die mich dazu bewegen, der Strahlung eine Art molekularer Konstitution zuzuschreiben"). The paper is Einstein 1909b (Vol. 2, Doc. 56). The source of this document is the description of an ALS in the Karl und Faber dealer cat- alogue 89 (spring 1964), lot 2657. [22 357]. 148. From Johannes Stark Aachen, Lütticherstr. 189. 8. IV. 09. Sehr geehrter Herr Kollege! Ich danke Ihnen für Ihren freundlichen Brief.[1] Wenn es mich auch sehr ge- freut hätte, Sie zu gewinnen, so mußte ich doch eine Ablehnung von Ihrer Seite erwarten.[2]
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