James Prescott Joule (1818-1889), born into a well-to-do family prominent in the brewery industry, studied at Manchester under Dalton. At age twenty-one he published the "I-squared-R" law which bears his name. Two years later, he published the first determination of the mechanical equivalent of heat. He became a collaborator with Thomson and they discovered that the temperature of an expanding gas falls. The "Joule-Thomson effect" was the basis for the large refrigeration plants constructed in the 19th century (but not used by the British brewery industry). Joule was a patient, methodical and devoted scientist; it became known that he had taken a thermometer with him on his honeymoon and spent time attempting to measure water temperature differences at the tops and bottoms of waterfalls.