434 
MR. E. H. GRIFFITHS OH THE VALUE OF 
One assumption underlies all the calculations, viz., that whatever the mass of the 
contained water, the water equivalent of the calorimeter remains constant.* "We 
find this assumption is not correct, unless the water is thrown against every part of 
the calorimeter throughout each experiment. At first sight it would appear that, 
whatever might be the “lag” of any unwetted portion of the calorimeter when the 
flo V of heat had become steady, the quantity of heat absorbed by it for each rise of 
1° C, would be the same, and that it would only be at the commencement of each 
experiment that differences would be observable. It must, however, be remembered 
that the radiation coefficient of the whole calorimeter would be altered by the exist¬ 
ence of this colder portion; and, as this cause of error would continue to exist 
throughout the whole experiment, the effect would be appreciable. 
In 1891 we adopted a new form of stirrer. An ebonite shaft, passed dovm the 
central tube, and terminated at its lower extremity in an agate point, which rested 
on a metal hearing on the base of the calorimeter. Two gold tubes joined together in 
the form of a V were fastened to this shaft, the apex of the V being downwards and 
immediately above the agate point. This stirrer acted as a centrifugal pump, and, 
when revolving at a rate of about 1200 per minute, threw the water upwards and 
outwards with great rapidity—the whole contents of the calorimeter being removed 
in a few seconds when the lid was off. There could be no doubt that, provided there 
was sufficient water to at all times cover the lower openings of the tubes, the stu-ring 
was sufficient, and that no portion of the calorimeter could remain for any appreciable 
time at a different temperature to the water. This form of stirrer appeared to us so 
satisfactory that we did not attempt to improve upon it during our experiments in 
1891 ; and it was this misplaced confidence which was the chief cause of our failure, 
in that year, to obtain satisfactory results. 
Its defects may shortly be summed up as follows :— 
(1.) As the depth of water in the calorimeter increased, the work expended in 
forcing the tubes through the water also increased ; and the rate of rise in tempera¬ 
ture (which ought to have dmrinished) was much greater when the mass of the water 
was large. 
(2.) This change in the quantity of heat developed would not have been fatal, since 
it could have been determined separately for each mass of water used, and we per¬ 
severed in our attempts to thus determine it. Unfortunately, however, it varied 
capriciously, even when the mass of water and rate of revolution were constant; and 
we have never arrived at any satisfactory explanation of these variations. It appears 
probable, however, that their origin was due to differences in pressure between the 
* If the water equivalent varies, the fact is rendered very evident when the values of J deduced from 
different masses of water are compared. Until, in 1891, we adopted forms of stirrers which threw the water 
against the roof of the calorimeter, our experiments were rendered useless by this constant source of 
error. The agreement between the values obtained in 1892 is a satisfactory pi’oof that this difficulty 
had been overcome. 
