1888 - 89 .] Mr John Aitken on Dust Particles. 
159 
this purpose a situation was sought which, while it could be easily 
got at, would yet he as far removed from human habitations as 
possible. Attention was afterwards directed to the condition of 
the air in densely populated areas. 
The best set of observations I have yet obtained, in what may 
be called pure air, were taken at Colmonell, in January of this 
year. During my visit of a few days there were examples of most 
types of weather. I may mention that Colmonell is a small village 
in the south of Ayrshire, and is situated in a pastoral district, 
which is very thinly peopled. During most of the time of my visit 
the wind was southerly, and the air tested must have been fairly 
free from artificial pollution, as it had travelled from 20 to 40 miles 
— according to the direction — over the bare and uncultivated hills of 
Wigtown and Kirkcudbright before it arrived at the testing place. 
Along with this paper is given a table showing the results of 
recent observations. In the table is entered the place of the ob- 
servation, the date, and the hour when the tests were made. The 
results are given in numbers per cubic centimetre, and also per cubic 
inch of the air — the state of the weather at the time being entered 
in the last column of the table. By a reference to the table, it will 
be seen that the Colmonell observations show the air of that 
situation to be very free from dust, and that the air near Falkirk is 
very highly polluted by artificial causes. 
We shall now discuss the Colmonell observations in detail. It 
will he seen from the table that the morning of the 7th, when the 
observations began, was foggy. This fog was general all over the 
country. The number of particles counted at 10 a.m. on that day 
was 5350 per c.c. As the day advanced the fog cleared away, and 
the number of particles fell to 2500, or about one-half of what it 
was in the morning. Next morning (the 8tli) was dull and wet, and 
the numbers went up to about what they were on the morning of 
the previous day. The day continuing very stormy and wet, the 
air became very thick. On testing at 5 p.m. the dust particles were 
found to have increased, and the number now was 9500. On the 9th 
but few observations could be made, owing to the direction of the 
wind bringing the smoke of the village in the direction of the testing 
place. On the morning of the 10th there was a slight shower; the 
air was clear, and the sun bright. By 1 2 o’clock the great impurity 
