ABSTRACT
On Friday 30 May 1941, Bart Saris received his doctorate from Leiden University for a thesis on thermal conductivity in liquid helium II (the superfl uid form of helium). His offi cial supervisor was the physics professor and laboratory director Wander Johannes de Haas.1 This was a typical Leiden research project focusing on temperatures just above absolute zero (–273°C), carried out at the world-famous Kamerlingh Onnes Laboratory. The Leiden cryogenic laboratory was founded by Heike Kamerlingh Onnes (1853-1926), who was the fi rst to liquefy helium (1908) and who discovered superconductivity (1911).2 At the time that the degree was awarded to Saris, The Netherlands had been under German occupation for a year. Articles on the subject had already been published in the Dutch journal Physica by Saris, Willem Keesom and Keesom’s daughter Annie.3 The last of these articles, authored by Saris and Keesom, had been submitted on 21 August 1940.4
In short, Saris had been forced to wait for his doctoral bull for some time. This was because of the closure of Leiden University on 27 November 1940, a direct response to a demonstrative student strike against anti-Jewish measures taken by the German occupiers. Offi cial educational activities came to a halt, and examinations and doctoral defences no longer took place.5 For those, like Saris, who were almost fi nished with their doctoral research, the situation was tremendously frustrating.6 At the urging of the Board of Governors, the Germans permitted examinations and defences once again starting on 30 April 1941, but reinstated the ban on 20 November of that year.7
