44 Reynolds and Moorby, Equivalent of Heat. 



where t.x. stands for the terminal correction to the heat 

 due to change of temperature of the brake, and 



C = conduction-constant per unit diff. of temperature. 



R = radiation-constant „ „ „ 



Also the total work done 



U = 27r{M + ;;/)(N2 - Ni), 



where 7;^ = error of balance of the brake. 



If the capitals H and U refer to trials with a 

 large turning moment on the brake, and the small letters 

 Jt and u refer to trials with a small turning moment, 

 then for the value of the mean specific heat of water 

 in mechanical units we have 



^ _U - ?/ 



The letter K is used here in preference to the usual nota- 

 tion J, since the constant obtained is not strictly the 

 same as that determined by Joule and other experi- 

 menters ; for it must be borne in mind that we are here 

 dealing with the mean specific heat of water between 

 the freezing and boiling points. 



6. The reliability of the measurements. 



I was personally responsible for every observation 

 taken, with the exception of the two readings of the speed 

 gauge taken at the beginning and end of each trial, and 

 also for the checking of all the apparatus used in the 

 research. 



The measurements fall generally under two heads. 



I. 



The measurement of work. 

 This involved the balance of the brake, the length of 

 the lever, the determination of the values of the weights 

 used in loading the brake, and the counting of the revo- 

 lutions. 



