282 MR. E. H. GRIFFITHS ON THE LATENT 
Section VI.—THEr DETERMINATION OF Sq. 
I will now describe the method of obtaining the value of the various terms im 
Equation I. (p. 272) by which the quantity of heat supplied during an experiment is 
ascertained. 
=q is the quantity whose accurate determination presented the greatest difficulty, 
therefore the apparatus was so designed as to reduce this term to as small dimensions 
as possible, and since many of the contrivances adapted to this end may, unless their 
purpose is explained, appear unnecessary and cumbersome, [ commence with this term 
in order to avoid repetitions. 
Had it been possible to so arrange matters that the temperature of the calorimeter 
at the beginning and end of an experiment should be absolutely unaltered, this term 
(=q) would have vanished, and in my earlier experiments, during which I endeavoured 
to determine the mass of water evaporated by passing the resulting vapour through 
drying bulbs, this condition was practically fulfilled, since it was always possible to 
stop an experiment at any time. I was compelled, for reasons which will be given 
later, to abandon this method of estimating M, and to adopt a method in whicha 
given mass of water was to be evaporated. The observer had, therefore, no choice as 
to the time when the experiment should be completed, and as the thermal balance 
could not be absolutely maintained throughout an experiment, it was impossible to 
ensure the identity of the initial and final temperatures. 
It was advisable, if possible, to so arrange matters (I.) that a small alteration in the 
quantity of heat should produce a considerable change in temperature, so that small 
differences in the thermal equilibrium might render themselves evident ; (II.) that the 
oscillation in temperature might be reduced to as small dimensions as possible ; (III.) 
that the difference, if any, between the initial and the final temperatures should be 
accurately measured. 
Although Nos. I. and II. appear contradictory, such is not the case, for the 
important matter was to ensure the equality of the thermal, as distinct from the 
temperature balance ; therefore, if small alterations in the former made themselves 
readily evident by changes in the latter, and if the latter changes were kept small, 
the desired end was attained. 
Within the calorimeter there were two agencies at work—the cooling due to the 
evaporation (which for convenience I shall henceforth venture to speak of as a “supply 
of cold”), and a supply of heat due to the current; therefore, unless some means were 
adopted of rapidly bringing the contents to a uniform temperature, the temperature 
gradient from the hotter to the colder portions would be considerable. It was thus 
necessary to completely fill the calorimeter with some liquid and to rapidly stir this 
liquid. 
Two objections to the use of water immediately presented themselves : (a) its great 
capacity for heat (which would have caused changes in the thermal balance to have 
