Alfred Kleiner

• 1. Introduction

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  Alfred Kleiner sent back Albert Einstein's doctoral dissertation with a single criticism: it was too short. Einstein added one sentence and resubmitted. Kleiner accepted it without further comment. That exchange appears in Carl Seelig's biography of Einstein. Kleiner was a Swiss physicist, born on the 24th of April 1849. His name turns up in virtually every Einstein biography, almost always in a secondary role. But Kleiner had a scientific life of his own. He occupied an institutional position that would become inseparable from Einstein's path to a doctorate. What kind of scientist was he, apart from that connection? And how did a particular set of arrangements at two Zurich universities put him at the center of that path?

• 2. One Physics Chair

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  Johann Jakob Müller supervised Kleiner's doctoral thesis at the University of Zurich in 1874. The thesis addressed the theory of intermittent retinal stimulation. Kleiner had already taken a teaching post as a Privatdozent four years before receiving the doctorate. By 1880 he had risen to Associate Professor, and by 1885 to Full Professor. Between 1875 and 1885 he also held a Privatdozent post at the Swiss Federal Institute of Technology. That institution was then called the Polytechnikum. His main research centered on measuring instruments; the foundations of physics interested him as well. From 1908 to 1910 he served as Rektor, the equivalent of Chancellor, at the University of Zurich. In 1915 he was designated Honorarprofessor, the title given to emeritus faculty.

  The University of Zurich had only one physics chair, and Kleiner held it. Until 1909 the ETH was not authorized to grant doctoral degrees of its own. A special arrangement allowed ETH students to obtain Zurich doctorates instead. Most physics dissertations by ETH students were supervised by H.F. Weber, Einstein's former teacher at the Polytechnikum. Weber's falling out with one particular student would eventually redirect that student to Kleiner.

• 3. Shielding Gravity

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  In the early 1890s, Kleiner turned to an experimental question. Could the gravitational pull between two masses be reduced by placing shielding material between them? Two students, Fritz Laager and Theodor Erismann, joined the project. The investigation was prompted by papers from Louis Winslow Austin and Charles Burton Thwing. After careful measurement, no effect greater than the experimental error appeared. Laager issued his findings in 1904. Kleiner published his own results in 1905, and Erismann followed with papers in 1908 and 1911. A negative result in a well-designed experiment is not a failure. It removes a class of possibilities and pushes theorists toward different explanations. Kleiner's career-long focus on precision measurement was exactly what these experiments demanded. The same willingness to take an unconventional question seriously would define his approach to a visiting ETH student within the decade.

• 4. Doktorvater

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  Einstein's first doctoral supervisor at the ETH was Heinrich F. Weber. In the middle of 1901, the relationship collapsed. That same period also brought Einstein into controversy with the physicist Paul Drude. Einstein switched to Kleiner and changed his dissertation topic from thermoelectricity to molecular kinetics. The switch offered no guarantee of a smoother path.

  In November 1901, Einstein showed Kleiner a first draft of his dissertation. In letters to Mileva Maric, he noted the frequent discussions he had with Kleiner on a wide range of topics. In a letter dated the 19th of December 1901, he described spending an entire afternoon with Kleiner in Zurich. He had been explaining his ideas on the electrodynamics of moving bodies. Kleiner advised publishing those ideas alongside an experimental method. Einstein recorded that Kleiner found the proposed method to be "the simplest and most appropriate one conceivable."

  In February 1902, Einstein withdrew the dissertation. A year later, he told his friend Michele Besso that "the whole comedy has become tiresome for me." By March 1903 he had changed his mind. A letter to Besso from that period already contained central ideas from what would become his 1905 dissertation.

  Kleiner was one of two reviewers when Einstein submitted the completed dissertation on the 20th of July 1905. His judgment was positive: the arguments and calculations were, he wrote, "among the most difficult in hydrodynamics." The second reviewer, Heinrich Burkhardt, Professor of Mathematics at the university, added that "the mode of treatment demonstrates fundamental mastery of the relevant mathematical methods." The dissertation was titled Eine neue Bestimmung der Moleküldimensionen, or A New Determination of the Molecular Dimensions. Some scholars have argued that Einstein avoided his own preferred statistical approach in the thesis, to win Kleiner's approval. Kleiner's role in Einstein's career did not end with the dissertation approval.

• 5. The 1909 Appointment

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  Alfred Kleiner was in the audience for a 1909 lecture Einstein gave at the University of Zurich on electrodynamics and relativity. He followed the lecture by recommending Einstein for a newly created professorship in theoretical physics. On the 7th of May 1909, the Regierungsrat des Kantons Zürich formally appointed Einstein as an associate professor. The appointment took effect from the 15th of October 1909, at a salary of 4,500 Swiss Francs per annum. Kleiner had watched Einstein's intellectual development for nearly a decade at that point. His recommendation was not incidental. Kleiner died on the 3rd of July 1916, seven years after Einstein took up the chair in theoretical physics.