208 Proceedings of Royal Society of Edinburgh. 
mountain, situated at a distance of five or six miles to the west of 
Alford. It rises in easy slopes from the east and south, though ! 
rather steep on the north and west, and attains a height of 1747 
feet. The early morning of the 9th had been very thick, hut it 
soon began to clear. On testing the air at 9 a.m., before beginning 
the ascent, it was found to have 3000 particles per c.c.; on arriving 
at the top of the hill the number was found to be much lower. At 
midday there were only 262 per c.c. by the first test and 336 by 
the second, which was taken shortly afterwards, each of these 
numbers being as usual the average of ten tests. On again 
testing the air at 2 p.m., two sets of tests gave the same average, 
namely, 475 particles per c.c. This gradual increase was probably 
due to local contamination. When the first tests were made the wind 
was south-west, and came over an uninhabited district, whereas by 
the time the last tests were made the wind had veered to the west- 
ward, and brought the smoke of the dwellings in the Don valley 
towards the hill top. The view from the hill on this day was fairly 
clear, the Cairngorms and Lochnagar being quite distinct, but seen 
through a good deal of haze, which was illuminated by a bright sun, 
shining in a cloudless sky. On returning to the foot of the hill and 
again testing the lower air it was found to have 900 particles per 
c.c. It seems therefore probable that the lower air at this situation 
is considerably contaminated by local causes. 
Dumfries. 
The last series of observations entered in the table were made at 
Isle, near Dumfries. The site of these observations is quite in the 
country, at a distance of six miles, up the Nith valley, from 
Dumfries ; it is not near any village, but is surrounded in all direc- 
tions by farm and other houses. The site being on the banks of a 
river, the air at it will have the peculiarities belonging to such situa- 
tions, such as greater humidity, less air circulation, and lower 
temperature at nights than at more exposed situations. 
An examination of these Dumfries figures shows the air at this 
situation to have been remarkably impure for a country district. 
It was probably much more impure than it generally is, owing to 
certain meteorological conditions prevailing during the time these 
tests were being made. The table shows that the air was very pure 
