The experiments of M. Regnault having been made by introducing water at a high temperature from a boiler into a calorimeter, containing water at a low temperature, and power exercised by the steam in the boiler in expelling the water was converted into heat by fluid friction, thus producing a rise of temperature in the calorimeter, for which allowance ought to be made in calculating the specific heat of liquid water from each experiment. Mr Joule's determination of the dynamical value of the specific heat of liquid water at low temperatures affords the means of calculating the correction required in each case.