X. Bakerian lecture. - on the mechanical equivalent of heat

Abstract

1. The determination by Joule, in 1849, of the expenditure of mechanical effect (7 72’69 lbs. falling 1 foot) necessary to raise the temperature of 1 lb. of water, weighed in vacuo, 1° Fahr. between the temperatures of 50° and 60° Fahr. (at Manchester), together with the second, in 1878, 772’55 ft.-lbs., to raise the temperature of 1 lb. (weighed in vacuo) from 60° to 6L° Fahr., at the latitude of Greenwich, established once for all the existence of a physically constant ratio between the work expended in producing heat and the heat produced; while the extreme simplicity of his methods, his marvellous skill as an experimenter, and the complete system of checks he adopted, have led to the universal acceptance of the numbers he obtained as being within the limits he himself assigned (1 foot), of the true ratio of work expended in his experiments in producing heat and the heat produced as measured on the scale of the thermometer on which he spent so much time and care.