III. The mechanical equivalent of heat

Abstract

Dr. J. K. Roberts and the senior author of this paper began experiments upon the mechanical equivalent of heat in 1918. Mr. Roberts left Australia in 1920, and in that year he published an account of the principles of the design of the induction dynamometer which we have used. The experiments have been continued by the authors of this paper, but so many difficulties have had to be overcome to attain high accuracy as to make the investigation a prolonged one. What may be called the electrical equivalent of heat has been the subject of the wellknown investigations of Griffiths, Schuster and Gannon, Callendar and Barnes, W. R. and W. E. Bousfield, and Jaeger and Steinwehr. One of us has given a critical discussion of these experiments, and has corrected the previously published results to the thermodynamic scale of temperature, and the electrical units used to their now accepted absolute values. The direct determination of J has received much less attention ; for, in addition to Joule's original experiments, there are only those of Rowland, and Reynolds and Moorby.