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Proceedings of the Royal Society of Edinburgh. [Sess. 
as 20,000 per c.c., while the numbers remained low at the water’s edge. At 
the end of the observations, when the sky was cloudless, the numbers at the 
water’s edge had risen to over 1000 per c.c., or ten times their original 
number. This increase was probably due to sun-formed nuclei brought from 
the shore on the other side of Loch Linnhe by the inshore wind. These 
high numbers at the water’s edge would probably have come sooner, but 
the high hills across the loch kept that side clouded to a much later hour 
than the Appin side. It will be noticed that the numbers did not rise so 
high on this occasion as they did on the previous visit. The highest reading 
in the October visit was 40,000, while in July it was 150,000 per c.c., a 
result easily accounted for by the weaker sunshine of October compared 
with that of July, and by the air arriving pure at the foreshore on the 
former date. 
It cannot be said that this second visit to Appin gave any suggestion 
as to how these nuclei were produced on the foreshore, while it added 
difficulties, since it showed that they were not steadily produced, as one 
might expect if they were formed by sunshine out of something which 
was being evaporated by the heat. The tests clearly indicated that their 
production, instead of being a steadily increasing and decreasing quantity, 
was a very spasmodic one. The shore tests, at times when the sun was 
shining occasionally, only gave low numbers, one or two hundred per c.c. ; 
then these would suddenly increase and rise to thousands for a short time, and 
then again disappear, to return again in a little while, but the high figures 
never remained steady for long. This rapid variation in the numbers 
may be explained in two ways : either the production is spasmodic, or it 
is constant but very local and the variation in the numbers is to be 
explained by a slight shifting of the wind, causing the nuclei to be carried 
direct to the observer or made to pass to one side of him. 
In the Kingairloch observations the abnormally high readings were 
generally observed in N. W. winds ; and perhaps some explanation is 
necessary of why N.W. winds are so frequent at that station, while winds 
from W. and N. are rare. The cause of this is the geographical situation of 
Kingairloch, which is near the opening of a deep valley between high 
mountains. This valley has a trend to the N.W., so that all winds from N. 
to W. are deflected by the mountains and blow down the valley, arriving 
at Kingairloch as north- westerlys. An examination of the map of the 
country to the west and north of Kingairloch shows it to be full of sea 
lochs and islands ; so that there is a large area of foreshores, over which the 
air passes before arriving at Kingairloch, on which the sun may act and 
produce nuclei in the same way as has been found at Appin. 
