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Peter Debye in 1936

festively flagged. The guests, from imperial about him with regard to his home and abroad, include the Dutch institute.” At his first meeting with his physicist Peter Debye. With his wife, he students, the young lecturer was able is the guest of Alfred Kleiner, the head “with some difficulty, finally to agree of the Institute. There is plenty a time for his lectures.” Debye ­ended to talk about: For three semesters, from his brief report with praise for the city spring 1911 to summer 1912, Debye, as of Zurich: “Zurich itself is charming; ’s successor, occupied the sunset this evening was truly the Chair for Theoretical Physics at the wonderful.” University, first as associate professor, In Munich, Professor Sommerfeld then as full professor. And the Univer- and his wife had taken on something sity still hopes to entice its professor of a parental role for Debye. His actual to return. But Debye knows what he’s parents were distanced from academic 1936 “for his worth. Negotiations prove difficult and life. Sommerfeld once described De- contributions to our knowledge of molecular in 1915 are broken off altogether. No- bye as his greatest discovery in physics, structures through his investigations on body then has any idea that a couple and the young researcher’s outstand- moments and the of X-rays of years later Debye will return to join and in gases” the “competition” at ETH. “Debye is an excellent acquisi- The first time he came to Zurich, * 24 March 1884 in tion for the .” Peter Debye was 26, and the associate † 2 November 1966 in Ithaca, NY Wilhelm Conrad Röntgen professorship at the University was 1911–1912 Professor for Theoretical Physics at his first teaching appointment. He had the University of Zurich been recommended for this first aca- ing talent quickly became obvious in demic position by the physicist Arnold Zurich. On 10 December 1911, Debye Sommerfeld, who had become aware wrote to Sommerfeld in Munich: “Dear of the young man’s talents in Aachen, Sommerfeld, In the last 48 hours I have where Debye studied. When Sommer- discovered something really special.” feld went to Munich, Debye became This “something special” was to occupy his assistant. Wilhelm Conrad Röntgen, Debye for 40 years, and also become the The Leonardo who was also teaching in Munich, gave basis for his Nobel Prize in 1936. It was him an excellent reference: For the Uni- the idea that there are that of Physics versity of Zurich, Debye represented are permanent electrical . The April 1914: The University of Zurich cel- “an excellent acquisition.” “dipole moment” of a substance can ebrates the opening of its new univer- On a postcard depicting Zurich and be measured, and enables conclusions sity building, whose impressive tower the Alps, in 1911 Peter Debye offered as to its molecular structure. The brief now overtops the neighboring ETH Sommerfeld his first impressions. He period of Debye’s activity at the Uni- building. In honor of the occasion, the was looking for accommodation, “a versity saw more fundamental work Zurich guilds dedicate “Sechseläuten,” very boring business.” Alfred ­Kleiner, based on the hypothesis of permanent their traditional spring procession, to under whom he worked, was “very dipoles, for example, on the behavior of the history of knowledge. The city is nice,” but there was “something a bit molecules when temperature changes.

www.nobelpreis.uzh.ch/en_debye.html Peter Debye – Nobel Prize in Chemistry 1936 1/4 Debye was not only a brilliant re- had first proposed, accepted ­Zurich’s 1920 he returned to Zurich. In the end, searcher, he was also a good teacher. offer, but then began to make additional he was given several special allowanc- His lectures and experiments – in those demands, which delayed his appoint- es, including “period of service credited days part of the job specification for a ment. This seriously annoyed Debye, from 1911.” This time he would stay in theoretical physicist – were always per- who was forced to come to the assis- Zurich for seven years. fectly prepared and his humorous style tance of “good old Kleiner” and remain Debye’s two periods in Zurich were enabled him to communicate complicat- in ­Zurich for the summer semester. very different. At the University, he was a ed content with apparent ease, making In addition to the “tiresome Laue new and inexperienced associate profes- him much loved as a teacher. He himself business,” there was another topic in sor. He came to ETH already famous as a seemed to possess unlimited powers of the spring of 1912 that stirred Peter physicist, and had to take on numerous scholarly comprehension, and became Debye’s emotions. On this subject, he duties as head of department. He was known for his frequent remark of “But preferred to write, somewhat bashfully, also a father: His son, Peter Paul, born in it’s really quite simple!” to Sommerfeld’s wife. This particular 1916, was joined, in Zurich, by his daugh- Barely a year after his arrival in affair of the heart concerned Mathilde ter Mathilde Maria in 1921. As a Univer- ­Zurich, Peter Debye reported to his sity professor, Debye had lived at Bol- mentor in Munich that “after much in- leystrasse 50; now, the family lived first “But it’s really quite simple!” – ternal struggle” he had accepted an ap- in a new building at Walchestrasse 19, Peter Debye’s powers pointment at the University of Utrecht. but then moved to Zürichbergstrasse 4. of scholarly comprehension Kleiner, the head of the institute, wrote Despite his many duties, Debye was seemed limitless. to Sommerfeld that he greatly regretted able, together with his assistant, Erich the departure of his “dear colleague Hückel, whom he had brought with him Debye,” who had “become our pride Alberer, the daughter of his previous from Göttingen, to publish important and joy.” His students tried in vain landlord in Munich. It had not escaped work in physics. On his recommenda- to change his mind with a torchlight the notice of his colleague in Zurich. tion, another Göttingen colleague, Paul procession. Debye set out the reasons “Debye is currently living in seventh Scherrer from St. Gallen, joined ETH as for his decision in detail in his letter heaven,” Kleiner reported to Sommer- professor for physics. In 1915 they had to Sommerfeld, including criticisms of feld. The latter now offered his previ- jointly developed the Debye-Scherrer the situation in Zurich. He had endea- ous pupil the paternal “Du” form of method, an experimental method for vored to ensure that “the large salary address. The 28-year-old professor was determining the structure of pulver- offered by the University of Utrecht did soon engaged to Hilde, though she was ized using X-rays. Scherrer re- not cloud my judgment.” Other reasons still at a boarding school in Les Brenets mained in Zurich till he retired, and, weighed more heavily: “I saw that in in the Canton of Neuchâtel. They were together with Debye’s successor, Wolf- Zurich I would undoubtedly have to married in Munich, on 10 April 1913. gang Pauli, would shape the course of sacrifice years to get a laboratory more As the position in Utrecht did not physics in Zurich for decades to come. or less in order … in Utrecht, I am not come up to Debye’s expectations, in In 1927 Debye was offered an ap- obliged to worry about experiments; I the fall of 1914 he accepted a professor- pointment in Leipzig at such attractive will not need to ensure, day by day and ship in Göttingen, where he remained conditions that ETH neither could, nor as tactfully as possible, that people do throughout the First World War. As a would, match them. Debye rapidly made not try to base their work on outdated, Dutch national, he was not conscripted the Leipzig Institute one of the leading impossible ideas.” and was able to continue researching, addresses for physics. In 1933, for the Debye’s hope that a successor for his if with limited resources. However, second time after Zurich, he had the op- professorship in Zurich could be found the precarious conditions in post- portunity to take over a chair previous- by the beginning of the summer semes- war ­Germany moved him to consider ly occupied by Einstein, who resigned ter 1912 was not fulfilled. , ­applying for the vacant Chair of Physics for political reasons from his position as a student of Sommerfeld’s whom Debye at ETH. After a tussle over his salary, in director of the ­Kaiser-Wilhelm-Institut

www.nobelpreis.uzh.ch/en_debye.html Peter Debye – Nobel Prize in Chemistry 1936 2/4 für Physik in . The award of the Calculated in Zurich: gases. After Max von Laue’s discovery, in Nobel Prize in Chemistry in 1936 fur- The Forms of Molecules 1912, of the diffraction of X-rays on crystals, ther enhanced ­Debye’s reputation: He Debye was able to extend this method to served Germany’s­ new rulers as a sym- Peter Debye was described by his colleagues crystalline powder, to liquids, and ulti- bol of the quality of German science. at as the “Leonardo Da mately, in 1928, to gases. He undertook When, however, in the fall of 1939 Vinci” of the 20th century. Many methods these investigations in Göttingen, with the authorities demanded that he ei- and laws in physics bear his name. The the Swiss . They also achieved ther renounce his Dutch citizenship “Debye temperature,” for example, comes similar with beams, or retire, Debye saw himself forced to from his theory concerning the specific heat though this method above all offers insights act. He took leave in order to accept a of bodies, which he developed at the into atomic nuclei. visiting professorship at Cornell Uni- University of Zurich. “Debye” also became Did Debye perhaps inspire the work versity in Ithaca, traveled to the USA the name of the unit for the electric dipole behind Erwin Schrödinger’s 1933 Nobel in January 1940 – and remained there moment. The discovery and measuring of Prize in Physics? , Nobel Physics for the rest of his life. But when, after the dipole moment was mentioned explic- laureate in 1952, as a student attended a the war, he returned to Europe to lec- itly in the motivation for his Nobel Prize, and colloquium led jointly by Debye and his was also the reason why, as a physicist, he University colleague, Schrödinger. Accord- was awarded the Chemistry Prize. For chem- ing to Bloch, in 1926 Schrödinger, inspired Peter Debye developed an ists, this represented a new and important by Debye, talked about waves; Debye said experimental method for possibility for determining the structure of that waves required the establishment of determining the structure of molecules. Debye had first concerned him- a wave equation – and a few weeks later, pulverised crystals. self with the subject in 1911, during his time Schrödinger presented exactly that. (MW) as professor at the University of Zurich. ture, Debye filled the auditoriums, not Whether a has a dipole least in Zurich. “With his unshakeable moment depends on its form. Thus, a water temperament, he knew how to present molecule, with the chemical formula H2O, a problem with unsurpassable clarity is an electric dipole; the gas CO2, on the and solve it with astonishing elegance,” other hand, not. Why is this? In CO2 the two Alfred Brunner wrote in his obituary in oxygen and the carbon to which the NZZ. Margrit Wyder they are linked are in a straight line. This neutralizes their charges. With the water Source: Margrit Wyder: Einstein und Co. – Nobelpreisträger in Zürich; Verlag NZZ libro, molecule, by contrast, the two hydrogen Zürich 2015 Illustration: Aline Telek atoms linked to the oxygen atom form an Translation: University of Zurich angle, so that the charges do not cancel out and an electric field is generated that can be measured. Conversely, the measurement of this dipole moment enables conclusions about the spatial structure of a molecule. Debye was able to conduct such measure- ments during his second period in Zurich, as professor at ETH. He was, for example, able to calculate that the ammonia molecule with the formula NH3 must have a pyrami- dal form, as shown in his illustration. A further reason for the award of the Chemistry Prize to Debye was his work with

www.nobelpreis.uzh.ch/en_debye.html Peter Debye – Nobel Prize in Chemistry 1936 3/4 Peter Debye as a young instructor. Photo: ETH Library Zurich, archives

Peter and Hilde Debye on Lake Zurich in 1926. Photo: Courtesy Ava Helen and Papers, Oregon State University Libraries

www.nobelpreis.uzh.ch/en_debye.html Peter Debye – Nobel Prize in Chemistry 1936 4/4