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Einstein-Szilard fridge patent. This US patent (number 1,781,541) for a fridge design, filed on 16 December 1927, was granted on 11 November 1930. It is signed at lower right by the two inventors German-Swiss-US physicist Albert Einstein (1879-1955) and his former student Hungarian-born physicist Leo Szilard (1898-1964). Both were working in Berlin, Germany at the time. Their design was for an absorption refrigerator. It had no moving parts, operated at a constant pressure, and required only a heat source to operate. Einstein had worked at the Swiss Patent Office, and used his experience with patents to help register their invention. A total of 45 patents were granted. (KEYSTONE/SCIENCE PHOTO LIBRARY/US NATIONAL ARCHIVES/SCIENCE PHOTO LIBRARY)