1889 - 90 .] 
Mr J. Aitken on Dust Particles. 
207 
there. My visit was made on the 1st August under fairly favour- 
able conditions of weather. The morning was dark and cloudy, 
with detached patches of mist on the hill-sides. Fortunately as the 
day advanced the mist gradually rose, and as I ascended the 
mountain it cleared away and at last was all gone by the time 
the top was reached. The air was fairly clear, as we could see 
Schiehallion quite distinctly on the one side and the hills of Skye 
on the other, the whole horizon within that range being clearly visible 
all round. The day, however, was favourable for transparency, as the 
sky was clouded all over and the sun did not shine on and illumin- 
ate the little haze there was in the air. On testing the air the 
number of particles counted by Mr Omond and myself was 335 per 
c.c. at 1 p.m. and 473 at 3 p.m. 
Alford. 
Observations were made from the 5th to the 15th September at 
Alford, a small village in the valley of the Don in Aberdeenshire. 
These tests were made near the Manse of Alford, which is situated 
at a distance of about 2 miles to the west of the village. There are 
but few houses near, so that the air would be fairly free from local 
pollution. An examination of the figures given in the table for this 
situation shows that the air here was not quite so pure as at 
Kingairloch. This might possibly be due to there being more houses 
in this locality than in the neighbourhood of Kingairloch, but part 
was also due to the weather. While these tests were being made 
the wind was generally very light, and frequently blew from the 
east and south-east, that is from the polluted districts, and it rarely 
came from the mountains, so that probably the air was a good deal 
polluted; and, moreover, owing to the wind being generally light, the 
air was stagnant and local pollutions would tend to accumulate. It 
is probable that the numbers given for this situation are too high 
for an average for the district, as the weather at the time was close, 
dull, and thick, with a marked absence of the usual clear crisp 
Aberdeenshire air of September. 
On the morning of the 9th the wind blew from the south-west, 
that is from an unpolluted direction; it was therefore determined 
that an ascent of Callievar should be made that day, for the purpose 
of testing the air at the top. Callievar is a somewhat isolated: 
