276 MR. EH. H. GRIFFITHS ON THE LATENT 
in estimating 3/5 of the micrometer divisions, and thus readings could be taken to 
‘01 millim., that is to about ‘0004° C. on A and to about *0005° C. on No. II. 
I do not, of course, claim that I could determine actual temperatures to this 
closeness, by these or any other mercury thermometers, but, owing to the precautions 
above described, I have no doubt but that changes in temperature of the order of 
0°-001 C. (2.e., about *025 millim.) could be detected, especially as any movement was 
extremely slow—in no case as much as 0°01 C. per hour. A constant vibration, 
due to the pumping of the water up the surrounding tube, tended to prevent 
“ sticking.” 
A further improvement has been the addition of a gas pressure regulator. This 
apparatus was designed for me by Mr. Horace Darwiy, and is the only satisfactory 
instrument of the kind I have seen. It is most perfect in its action, and J am now 
absolutely indifferent to changes of pressure in the mains. 
With these additions, I think that the whole of this constant temperature portion 
of the apparatus may be considered as nearly perfect. Only those who have watched 
it actually at work can appreciate the certainty of its action; it can be set with 
precision to any temperature between that of the tap-water and 64° (the highest 
temperature at which I have actually tested it), and my only regret is that cir- 
cumstances compel me to leave unused, for the greater portion of each year, 
apparatus by means of which so many difficulties could be overcome. 
Section V.—DESCRIPTION OF THE CALORIMETER AND ITS CONNECTIONS. 
The calorimeter was made of brass and was of cylindrical form, 10 centims. in 
diameter and 10 centims. in height. 
It contained a silver flask, F (see Plate 5, fig. 1), in which the evaporation took 
place ; a stirrer, of which the lower end only is shown at 8; a rack (shown in the 
horizontal section, Plate 5, fig. 2) which carried a coil of platinum-silver wire, and 
about 18 feet of silver tubing wound in a spiral—shown in section at p.p’. A 
platinum thermometer also passed from the top to the bottom. With so many 
objects crowded into so small a space, it is difficult to convey any clear idea of the 
internal arrangements, therefore I will only attempt a brief description, and shall 
rely chiefly on the sections given in Plate 5 to convey the necessary information. 
The capacity of the flask, F, up to the side opening at d, was about 68 cub. centims. 
Any vapour or gas passing from the flask into the spiral at d, after descending to the 
bottom of the calorimeter, ascended throughout the whole length of the coil, and 
thence up the tube e. This arrangement was adopted to diminish any chance of the 
carrying of the liquid, or “priming,” by the flow of vapour or gas, as it appeared 
improbable that particles of liquid would be carried up a gentle slope of 18 feet in 
length. 
