LIST OF TEXTS xix 249. To Carl Schröter, 21 January 1911 250. To Hendrik A. Lorentz, 27 January 1911 250a. To the Association of Students of the Natural Sciences, University of Amsterdam, 28 January 1911 251. To Emil Zürcher, 29 January 1911 252. To Friedrich Adler, 9 February 1911 253. From Richard Swinne, 12 February 1911 254. To Hendrik A. Lorentz, 15 February 1911 255. From Günther Beck, 16 February 1911 256. To Edgar Meyer, 26 February 1911 257. To Richard Swinne, 26 February 1911 258. To Lucien and Jeanne Chavan-Perrin, 10 March 1911 259. To Hans Schinz, 10 March 1911 260. To Lucien Chavan, 28 March 1911 261. To Conrad Habicht, 2 April 1911 262. To Lucien Chavan, 5 April 1911 263. To Heinrich Zangger, 7 April 1911 264. To Paul Ehrenfest, 12 April 1911 265. To Hans Tanner, 24 April 1911 266. To Marcel Grossmann, 27 April 1911 267. To Michele Besso, 13 May 1911 268. To Heinrich Zangger, 7 June 1911 269. From Ernest Solvay, with an Invitation to the Solvay Congress, 9 June 1911 270. To Walther Nernst, 20 June 1911 271. To Lucien Chavan, 5-6 July 1911 272. To Zürcher and Furrer & Co., 11 July 1911 273. To the Eleventh Congress of Polish Physicians and Natural Scientists, before 21 July 1911 274. From Alfred and Clara Stern, 2 August 1911 275. To Jakob Laub, 10 August 1911 276. To Michele Besso, second half of August 1911 277. From Willem Julius, 20 August 1911 278. To Willem Julius, 24 August 1911 279. To Heinrich Zangger, 24 August 1911