310 MR. HE. H. GRIFFITHS ON THE LATENT 
temperatures approximating to 40°; Table XII. those at temperatures near to 30°; 
and Table XIII. two experiments at 30°, where the rate of evaporation was but 3% of 
the former rate. Any inaccuracy in the values of Q,, ¢,, and =q would in these last 
experiments tell with double force. Also, the rate of evaporation being so greatly 
diminished, it was probable that any depression of the temperature of the evaporating 
water below @, would be about half of what it was when four cells were used, and 
thus the magnitude of any error, caused by such depression, would be indicated. 
Had time permitted, I should have repeated these experiments with a still slower 
rate of evaporation. I was, however, surprised to find that it was more difficult to 
maintain the thermal balance with the lower than with the higher D.P. 
A large number of differently shaped and sized “ droppers” were used, hence the 
difference in the values of M. 
As I preferred to alter the conditions as much as possible, no effort was made to 
keep the stirring rate the same for different experiments. 
In most cases the droppers when removed after an experiment appeared to be 
absolutely dry. In two cases, however, some signs of moisture were visible. I am 
at a loss to account for this, as I feel sure that evaporation had ceased, and that 
there was no water left on the surface of the silver flask. The moisture thus 
remaining was, of course, included in the final weighing, and would not therefore 
introduce any error provided the flusk was dry. It is noticeable, however, that the 
two experiments at the end of which this moisture was visible (Nos. V. and IV.) 
give, as shown by Table XI. (0), the highest values for L.* 
The value of d’ — d” will be noticed as unusually high in No. I. Here we had no 
idea of the time when the experiment would finish, and did not allow for the rise in 
6, caused by the introduction of the dry air at the end, hence the close of the experi- 
ment found 6, too high by nearly 0°°028 C. Also we could only approximate to the 
value of ¢,, having in the hurry of the initial experiment forgotten to mark the time 
of finish. The remembrance of a casual observation of the clock, however, enabled us 
to fix it approximately. An error of 100 seconds in ¢, would in that experiment 
produce an error of not quite + °25 in L, and the value assigned to ¢, is probably 
within a minute of the truth. 
During Experiment II. a portion of the mercury covering the core of tap T; became, 
owing to careless manipulation, sucked into the apparatus, and in some unexplained 
manner stopped the evaporation for nearly ten minutes, during which the electric 
current had to be switched off. However, the accident had but little effect on the 
resulting value of L. 
No. XI. was an almost perfect experiment, the thermal balance being maintained 
very closely throughout. I do not think that the variations in 6, during this experi- 
ment at any time amounted to 0°-005 C., and the external temperature (@,) remained, 
* Even when the same dropper was used, and the bulb was afterwards found to be dry, the values of 
M were not identical. The mass of contained water depended on the temperature of the dropper when 
removed from the beaker after filling, and as the beaker was only roughly brought to a temperature 
somewhat above 6,, the values of M varied. 
