DOCUMENT 178 SEPTEMBER 1909 209 Ist der Strom gross gegen den gewöhnlichen Sättigungsstrom (i0 = nne), so ßj ^ 2(3/ verschwindet e gegen ea = e , sodass das zweite Glied von (4) wegfällt. Man findet dann aus (4) durch einsetzen der Werte / Ai = l ·2 El 0 1 - Xk\ X 0 V J oder für die Schwankung der Stromstärke A2 = i2e r k\ i o i-, V / Macht man die angegebene Vernachlässigung nicht, so findet man / Xk\ A] = i0e 1 - e x, V 2 0 J l0 l l 0 Sie sehen also, dass das Resultat wesentlich von dem Ihrer Betrachtung ab- weicht. Ich bin neugierig, wie sich dasselbe zum experimentellen Befund ver- hält. Interessant ist, dass die geometrischen Verhältnisse auch hier herausfal- len aus den Resultaten. Es grüsst Sie herzlich Ihr A. Einstein. Freundlichen Gruss an Herrn Stark und an Ihre Familie.[6] ALS (Christine Magun-Meyer, Bern). [75 592]. [1]This letter is dated on the assumption that it was written in the week after Einstein's re- turn from the Salzburg meeting. [2]Einstein gave a major address on the nature and constitution of radiation (see Einstein 1909c [Vol. 2, Doc. 60] for its published version), as well as participating in discussions on four lectures, including his own, at the 81st meeting of the Gesellschaft Deutscher Naturfor- scher und Ärzte in Salzburg a week earlier. [3]The consideration below refers to Meyer's work on the measurement of fluctuations in radioactive decay. These fluctuations were measured through fluctuations in the ionization cur- rent produced by a radioactive source emitting y-rays. Two processes are involved here: first the y-rays ionize atoms and then the electrons liberated by the first process cause secondary ionization by colliding with other atoms. Although both processes are subject to fluctuations, the first calculation below, which is published in Meyer, E. 1910a, only deals with the first kind of fluctuations. A is the fluctuation in the number of effective, i.e., ionizing collisions, W de- notes the probability that an electron ionizes a neutral atom, Z is the total number of electron- atom collisions, is the mean free path of the electrons, Xk is the free path of a particle with sufficient energy to cause ionization, and i is the ionization current. See also Meyer, E. 1908, 1909 for Meyer's earlier experiments. [4]In Meyer, E. 1910a, in a section, entitled "Shortcomings of the Theory" ("Mängel der Theorie"), Meyer acknowledges that Einstein pointed out to him that the number of electron- atom collisions Z also undergoes fluctuations. [5]Quadratic terms in ß are neglected. [6]Johannes Stark Else Meyer (1884-1964) and son Edgar Michel (1907-1969).