Electromagnet according to Weiss, c. 1930, Siemens & Halske, Berlin From the Physics Laboratory of the University of Leiden
Inv V09685

For magnetic research the Physics Laboratory had long wanted a very large electromagnet. But in 1926 an additional reason emerged: a means had been devised of reaching very low temperatures with the aid of magnets, and low-temperature research was also a Leiden tradition. So that the magnet had to come. However, there was a problem with large electromagnets: the larger they were the more easily they overheated. This was finally solved by making the electric wiring from copper tubing, through which cooling water could be pumped. While this made the magnet extra cumbersome and heavy, that was preferable to its melting. All in all it became an instrument weighing 14,000 kg. And bear in mind that the specimens that were cooled down with it weighed approximately one gram.