300 MR. E. H. GRIFFITHS ON THE LATENT 
or when the swing was the same as the initial one. The taps T, and T,, were then 
turned so that the dry air instead of passing through the tank, &c., went straight 
through T, to the weighing bulbs, and thus any moisture left in the connecting tubes 
was swept into the bulbs. 
The swing of the galvanometer was rarely as much as 50 (indicating a difference of 
about 0°01 between @, and @) throughout one of these experiments, and when such 
oscillations occurred care was taken to alter the adjustments so that a swing to the 
right was invariably followed by a similar swing to the left. The whole apparatus 
could easily be managed by two observers and, on occasions, it was unnecessary to 
make an alteration of any kind for half-an-hour at a time. 
As before stated, the stirrer automatically recorded on the chronograph tape the 
time of each 1000 revolutions. 
The weighing bulbs were of peculiar construction and specially designed for this 
work. The gas passed through four washings of H,SO, and then through a tube of 
P,O;, on the further side of which was attached a CaCl, tube. The latter was not 
included in the weighings, but only used to prevent any access of the laboratory air 
to the P,O; when the gas current was not passing. The weighing bulbs were 
connected with the exit tube by a mercury trap* and had simply to be lowered into 
place, no. fitting of rubber tubes being necessary. To avoid condensation, the 
mercury trough and also the whole of the exit tube exterior to the tank were 
maintained at a temperature above 6, by means of small gas jets. 
At the close of an experiment the weighing-bulbs were removed (with their precisely 
similar tares) to the balance case. A careful weighing was made about an hour 
after the experiment, and again next morning; an apparent increase of about °0005 
gram generally presenting itself. 
As (especially in the stirring experiments) small differences in weight had to be 
measured, I took every precaution I could devise, and I also followed the suggestions 
of friends whose experience in this matter was greater than my own. The balance 
was a short-beam one by VERBECK and PEcKHOLDT, and was constructed so as to give 
aswing of 2°5 divisions per 1 milligram when loaded up to 500 grams. The actual 
weights to be measured were about 120 grams. I made special efforts to keep the 
temperature of the balance case steady, and noted the effects of changes in tempera- 
ture on the ratio of the arms, etc. 
The weights used were by Messrs. OFRTLING, and re-standardised by them last year. 
The increase in weight during the electrical experiments varied from ‘8 to 3°5 grams, 
the increase during the stirring experiments from ‘06 to ‘08 gram. 
I think it certain that the weighing error was neverso much as ‘002 gram, and it 
was probably much less; thus I do not believe that any discrepancies in the values of 
L greater than 1 in 1000 can be due to errors of this description. 
As before described (p. 291) the mass of water evaporated by the stirrmg supply was 
* Neither bulbs nor trough are shown in fig. 1, Plate 6. 
