272 MR. E. H. GRIFFITHS ON THE LATENT 
surrounding space, and I think I shall be able to show that this condition was 
fulfilled. 
In addition to the heat supplied by the electric current there is also a supply due 
to the work done by the stirrer. It was in the estimation of this “ stirring supply ” 
that I found my greatest difficulties, and I regard that portion of my determinations 
with the least confidence. Fortunately the heat thus generated was only about 797 
of the heat supplied by the current, and thus any small error in that portion of the 
work becomes of little account. 
Of the accuracy with which the electrical supply could be measured, there is no 
question, and I have but one remark to make on this portion of the subject, viz., that 
even if the values of the E.M.F. of my Clark cells, or the absolute resistance of the 
box-coils given by the standardisations performed during my determinations of J, are 
in any way inaccurate, such errors would eliminate, since the value of J was 
determined by means of the same standards as those by which the quantity of heat 
developed in these experiments was determined. Hence, by assuming my former 
value of J, I get the comparison in terms of a thermal unit at 15° C., independently 
of the numerical value of J assumed in the reductions. 
One further correction remains to be noticed. I have spoken of the temperature 
of the calorimeter as oscillating about the exterior temperature, and it might happen 
that at the close of an experiment this difference was not the same as that at the 
commencement—if any such difference existed. The magnitude of this correction 
depended, of course, on the ability of the observer to maintain the thermal balance. 
In these experiments the correction was extremely small, and in any case could 
be determined with great accuracy. 
Having indicated the nature of the observations I will proceed to state the relation 
between the various sources of loss, or gain of heat. 
Let Q, be the thermal units per second due to the electrical supply. 
» Qs »» »» 2 x mechanical supply. 
,, 2g be the total heat supply during an experiment from any other causes. 
Then, if M be the mass of water evaporated, L the latent heat of evaporation 
at temperature @, and if the electrical supply is maintained for a time ¢t,, and the 
mechanical for a time f,, 
ML = Q4, Qi to 2G i ye ee eS 
Now the D.P. at the ends of the coil was always some integral multiple of the D.P. 
of a Clark cell. 
Let e be the D.P. of a Clark cell, x the number of cells, and R, the resistance of 
the coil at the temperature 6,, then 
pr 
en 
Q. a Roe : : : sks . . . . . . (2). 
