[ 361 ] 
VI. The Value of the Mechanical Equivalent of Heat, deduced from some Experiments 
performed ivith the view of estahlishing the relation between the Electriccd and 
Mechanical Units; together with an Investigation into the Capacity for Heat 
of Water at different Temperatures. 
By E. H. Griffiths, M.A., Assistant Lecturer, Sidney Sussex College, Cambridge. 
Communicated by E. T. Glazebrook, F.R.S. 
Received January 19,—Read February 16, 1893. 
[Plates 2-4.] 
Contexts. 
Page. 
Introduction. 361 
Section I.—General description.367 
II.—The Calorimeter and Coil..373 
III. —The method of maintaining a constant temperature.374 
IV. —The motor and its connections.378 
V.—The pressure in the sixrrounding space.380 
VI. —The method of maintaining a constant E.M.F.381 
VII. —The measurement of resistance.388 
VIII.—The measurement of time.414 
IX.—The measurement of mass.415 
X.—The measurement of temperature.420 
XI.—The heat developed by the stirring.433 
XII.—The gain or loss by x’adiation, &c.441 
XIII. —The method of performing a J-experiment.456 
XIV. —The calculation of the results.477 
XV.—Discussion of the results.493 
Appendix I.—The determination of the “Null Point”. .... 500 
II.—A form of gas regulator.503 
' Introduction. 
The necessity for a re-determination of the value of the mechanical equivalent may 
not be obvious at first sight. The classic determinations by Joule have undergone 
but little alteration at the hands of succeeding observers, and the researches of 
Rowland (1879) into this matter were of such an exhaustive nature that there 
would appear to be little room left for further Investigation. It should, however, be 
MDCCCXCHI.—A. 3 A 5.6.93 
