254 Proceedings of Royal Society of Edinburgh. [sess. 
The air on this day being very pure, all the tests made are entered 
in the table, and not averaged, as is frequently the case on the other 
days. Of course, each of the tests given is as usual an average of 
ten readings. The lowest test gave 86 per c.c., being the number 
for the purest air yet observed by me. 
When this small number was obtained the barometric distribution 
was very complicated. While the tests were being made the cyclone 
of the previous days had passed away to the north-east, and an 
anti-cyclone had appeared on the west coast of Scotland. The air 
tested seems to have been true anti-cyclonic air, which was but little 
contaminated by local pollution. 
On the following day the wind was still northerly and slight, and 
the dust had begun to accumulate, the numbers increased to nearly 
three times what they were on the previous day. The air remained 
clear, as it was both pure, dry, and cold. 
Table showing the Number op Dust Particles in the Atmosphere. 
Place. 
Date. 
Hour. 
Number 
of Par- 
ticles 
per c.c. 
Wind. 
Tempera- 
ture. 
Humidity. 
State of 
the Air. 
Remarks. 
M 
Jan. 
° 
° 
j 
Garelochead, 
23 
3.30 p.m. 
2,360 
N.W. 0-2 
34 
3-5 
Clear. 
24 
11.45 a.m. 
725 
S.W. 1 
40 
25 
y 
Sky clouded. 
25 
11.30 a.m. 
700 
S.W. 6 
50 
5 
Thick. 
Hills visible to only 3 miles. 
1.0 p.m. 
925 
W.S.W. 7 
49-8 
5-8 
3.30 p.m. 
925 
W.S.W. 6 
48 
6-5 
Medium. 
,, to more than 10 
miles. 
27 
11.30 a.m. 
250 
N.W. 6 
41 
3 
Clear. 
Passing showers. 
28 
116 
N. 1 
40 
4-5 
Extly. clear. 
Clearest day observed. 
100 
,, 
Sky cloudless and sun brilliant. 
93 
}} 
95 
88 
1.0 p.m. 
86 
39 
4 : 75 
J J 
29 
11.30 a.m. 
253 ' 
N.W. 1 
42 
3-75 
Very clear. 
Sky dull, upper air thickening. 
