1892 - 93 .] Mr Aitken on Hazing Effect of Atmosffieric Dust. 89 
the exception of the area near and surrounding the town of Stir- 
ling. The other populous parts of the county are near Falkirk, 
principally to the north, east, and south of the point of observation, 
and in the area south of the west line are Campsie, Kilsyth, &c. ; 
while in the centre of the county are situated the Campsie Fells, 
the Kilsyth and Denny hills, and in the north part are the hills to 
the east of Loch Lomond, so that all north of the line drawn west- 
wards through Falkirk, with the exception of the small area near 
the town of Stirling, the county is but thinly populated. For this 
reason, in the Plate the population of Stirlingshire is shown in pro- 
portion to its density at different parts. 
If the line drawn westward from Falkirk through Stirlingshire 
be continued through Dumbartonshire, we shall find that almost the 
whole population of that county also is condensed into the area 
south of this line. In five of the towns situated to the south of this 
line, including Helensburgh, which is almost on the line, there are 
64,698 inhabitants, or more than two-thirds of the whole population 
of the county. And if we were to add to the above number the 
population of the small towns south of the line, we should find that 
all the area north of it is extremely thinly populated. From this 
we see that the whole area of Scotland north of the line drawn due 
west through Falkirk is very thinly populated. If we had repre- 
sented on the map the population of Stirlingshire and Dumbarton- 
shire- equally distributed over them, it would have been difficult to 
understand from such a map the great clearness of the west winds, 
as darkish areas would have extended some distance to the north of 
west. But by shading these counties in accordance with the distri 
bution of the population, we see that the west winds at Falkirk do 
not blow over any areas but those that are thinly populated. 
It will be noticed that the isatmid lines show a decided tendency 
to open out to the southward. If we examine a map of Scotland, 
it will be seen that the area from S.E. to S.W. of Falkirk is very 
much less densely populated than the areas to E. and W. of it. 
If the distribution of the population in the counties south of 
Falkirk had been represented in the Plate more in detail, a com 
paratively slightly shaded area would have extended over a consider- 
able district to the south of Falkirk. The approach of the isatmid 
lines on the east is probably due to the impurities brought from 
