354 
PROFESSOR 0. REYNOLDS AND MR. W. H. MOORBY 
PART II. 
On an Experimental Determination of the Mechanical Equivalent of the 
Mean Specific Heat of Water between 32° and 212 ° Fahr., made in 
THE Whitworth Engineerinc Laboratory, Owens College, on Professor 
Osborne Eeynolds’ method.— By William Henry Moorby, M.Sc. 
1. In view of the frequent and extremely careful and accurate determinations of 
the value of the mechanical equivalent of heat which have been made of late years 
hy different experimenters using different methods the present series of experiments 
may on first thoughts seem superfluous. There did, however, seem to be sufficient 
disagreement between the results previously published—more particularly between 
values of the equivalent, as derived from the direct methods described by Joule, 
Rowland, and Miculescu, and the indirect electrical methods of Griffiths, and 
Gannon, and Schuster, to warrant a new investigation into the value of this 
important constant, if the proposed new method of working should carry with it 
advantages not available in previous investigations. I was accordingly very glad to 
fall in with the wishes of Professor Reynolds that I should undertake a research 
bearing on this point on lines which he suggested to me in July, 1894. 
2 . In Part I., par. 3, a full description is given of the apparatus whose existence 
in the Whitworth Engineering Laboratory led up directly to the institution of this 
research into the value of the mechanical equivalent of heat. 
The advantages which the proposed method offered were briefly ;— 
(1.) The possibility of obtaining a result which in no way depended for its 
accuracy on the value of the scale divisions of the thermometers used in 
the measurements of temperature (Part I., par. 11). 
This was done by supplying a stream of w'ater to the brake at a tempera¬ 
ture of 32° Fahr., and there raising its temperature to 212° Falir. before 
admitting it to the discharge pipe where its temperature was again 
taken. 
(2.) A means of eliminating from the result all losses of heat due to radiation 
and conduction from the calorimeter employed (Part I., par. 32). The 
manner in which this elimination was accomplished is indicated below. 
Let U and u represent the quantities of work done in two trials which differed 
only in the moment of resistance offered by the brake—the number of revolutions of 
the encfine shaft and the duration of the trials being the same in each case. 
Also let H' and h' be the apparent quantities of heat generated in the brake in 
these trials. These quantities will be less than the true equivalents of the works 
U and a by quantities wbicli represent the losses of heat from the brake by conduc- 
