Manchester Memoirs, Vol. xlii. (1898) No. 6. 35 



Part II. 



On an Experimental Determination of the Mechanical 

 Equivalent of the Mean Specific Heat of Water 

 between S*^'^ and %\%° Fahrenheit, made in the 

 Whitworth Engineering Laboratory, Owens College, 

 on Professor Reynolds' Method. 



By William Henry Moorby, M.Sc. 



I. General plan of the Investigation. 



The Whitworth Engineering Laboratory, at the 

 Owens College, is supplied, among other apparatus, with 

 a 100 H.P. experimental engine, the whole of the work, if 

 desired, being absorbed by one of Prof. Reynolds' 

 hydraulic brakes. This brake maintains a steady turning 

 moment on the shaft, which we may represent by M, for 

 any trial. If N be the number of revolutions of the shaft 

 in any time, then the total work done in the interval is 

 U = 27rMN. The whole of this work is expended in 

 raising the temperature of a stream of water flowing 

 through the brake. 



Let W = total weight of water in the interval, and 

 ^T = rise of temperature in the brake ; then, neglecting all 

 losses by radiation, &c., the heat generated = H = W.^/T. 



For some years past experimental determinations of 

 the heat generated in the brake have been made to obtain 

 evidence of the adjustment of the brake, to the limits of 

 accuracy of the thermometers used, by equating the heat, 

 multiplied by 772, to the work as measured. The chief 

 difficulty met with in the endeavour to obtain reliable 

 results by this method was in the calibration of the scales 

 of the thermometers 



