In 1901, after living in Switzerland for five years, he acquired the citizenship of Zürich, and this at last gave him the opportunity of rising above material cares. His University friend, Marcel Grossmann, lent him a helping hand by recommending him to the Swiss Patent Office, the director of which was his personal friend. Einstein occupied himself here from 1902 to 1905 as a technical expert, that is, as an examiner of applications for patents, and this position gave him the chance of moving about in absolute freedom in the realms of technical science. Whoever has a strong predilection for discovery will perhaps feel estranged to find Einstein so long in the sphere of "invention," but, as Einstein himself emphasizes very strongly, both regions make great demands on clearly defined and accurate thought. He recognizes a definite relationship between the knowledge that he gained at the Patent Office and the theoretical results that appeared at the same time as products of intensive thought. In 1905, in the midst of his work, the storm broke loose in him with the suddenness of a hurricane. In quick succession his mind disburdened itself of the abundance of ideas that had stored themselves up in the work of the preceding years, and these ideas signify more to us than a definite stage in the development of an individual. What physicists have come to regard as an elaboration of the heritage of Galilei and Newton had matured in him. We merely record the title of dissertations, which appeared in 1905 in the _Annalen der Physik_: "Concerning a Heuristic Standpoint towards the Production and Transformation of Light"--"Concerning the Inertia of Energy"--"The Law of Brownian Movement."--Then the most important contribution: "The Electrodynamics of Moving Bodies," that contained the revolutionary ideas underlying the special theory of relativity. To these is to be added a dissertation for his doctorate in the same year: "A New Determination of Molecular Dimensions." In all, these represent a life-work that belongs to the history of science. It was certainly some considerable time before his work began its triumphal march in the sight of the world, and it may be added that treasures were hidden in these disquisitions that were not understood till long years afterwards. Yet the youthful discoverer was not passed over without signs of friendly appreciation. He received a letter, couched in very warm terms, from the celebrated physicist, Max Planck, who was a complete stranger to him at that time; it spoke in glowing words of his essay, "The Electrodynamics of Moving Bodies." This letter was the first diploma, the forerunner of all the honours that later swept over him like a tidal wave.