358 Proceedings of Royal Society of Edinburgh. [sess. 
for rest after the instrument has been wiped. The weighings were 
repeated at different times during each of the days March 19th 
to 25th inclusive, the pyknometer and counterpoise having been 
previously wiped and allowed to stand for five minutes, as already 
described; the barometer was read on each occasion. The proper 
corrections due for the buoyancy of the air were then applied to 
those weighings, which were performed without the aid of a 
counterpoise. The results obtained are given in Table I. 
Table I. 
Date. 
Time. 
Barometer. 
Reduced Wei 
A. 
With Counter- 
poise. 
ght of Water. 
B. 
Without 
Counterpoise. 
1902. , 
10 a.m. 
29 ‘77 inches 
50-0569 grms. 
50-0561 grms. 
\ 
11 a.m. 
Falling 
71 „ 
66 
Mar. 19th < 
1 p.m. 
slowly 
71 „ 
69 
3 3 
( 
7 p.m. 
29 '59 inches 
71 ,, 
71 
3 ? 
r 
10 a.m. 
29-20 „ 
69 ,, 
75 
Mar. 20th j 
1 p.m. 
29-18 ,, 
69 „ 
75 
3 3 
/ 
10 a.m. 
29-10 ,, 
68 ,, 
71 
Mar. 21st 1 
3 p.m. 
29-08 ,, 
68 „ 
73 
3 3 
[ 
10 a.m. 
29-10 ,, 
65 „ 
67 
Mar. 22ncl 4 
Noon 
29-10 ,, 
65 „ 
68 
3 3 
l 
8 p.m. 
29-18 „ 
65 ,, 
69 
3 3 
( 
10 a.m. 
29-38 ,, 
64 „ 
55 
3 3 
Mar. 24th \ 
1 p.m. 
29-30 ,, 
62 „ 
61 
3 3 
\ 
8 p.m. 
28-90 ,, 
62 „ 
66 
3 3 
Mar. 25th 
10 a.m. 
29-40 ,, 
63 „ 
53 
3 3 
On glancing down the column given under A, we notice (1) 
that, with the single exception of the observation made at 10 a.m. 
on March 24th, identical results are obtained at any time during a 
given day, even with a changing barometer ; and (2) that there is 
a very gradual and almost uniform falling-off in the weight of the 
pyknometer and its contents ; the loss, which is probably due to a 
continuous evaporation of water, is so slight that it only becomes 
a measurable quantity after the lapse of about twelve hours. On 
comparing the results given in column B, we note that there is 
