1889-90.] 
Mr J. Aitken on Bust Particles. 
209 
on the 30th of October, the number being as low as 235 per c.c., and 
it was fairly low on one or two other days, but on many occasions 
the number was over 5000 per c.c. The weather accompanying 
this impure atmospheric condition was true November weather, 
dull, thick, and damp, with only an occasional fine day. 
On the Pollution of the Atmosphere by Artificial Causes. 
On looking over the numbers given in the table one is struck by 
the amount of dusty pollution introduced into our atmosphere by 
human means ; and one cannot help feeling that the earth’s atmo- 
sphere is profoundly modified by the vast quantities of dust it 
holds in suspension, much of which owes its origin to the presence 
of human beings. When we ascend into the higher atmosphere, or 
go to uninhabited districts, the quantity of dust in the atmo- 
sphere is comparatively small, but whenever we approach human 
habitations the quantity increases, and near cities the air is 
laden with these floating particles. At the top of the Bigi, and in 
the wilds of Argyleshire, air was tested which had only a little over 
two hundred particles per c.c. On the top of Ben Nevis, on 
Callievar, and in Dumfriesshire, the number was occasionally only 
about three hundred, but when we get near villages, the number 
goes up to thousands, and in cities to hundreds of thousands. 
Though the number of particles in the atmosphere increases 
enormously as we approach the centres of human habitations, yet 
when we look more closely at the numbers in the table, we find that 
the increase, though great, is not by any means in proportion to the 
increase of the sources of pollution. A small village or town may 
make the passing air nearly as polluted as a large city. Now why 
should the pollution not be in direct proportion to the number of 
fires and other sources of contamination. Is it possible that when 
the number of particles becomes very great, so that they are very 
close together, that many may unite and form one 1 so that what 
we count as one, in city air, may really be a vast number adhering 
together. As yet we have no information as to whether these very 
fine dust particles ever do attract and adhere to each other or not. 
There is, however, an evident reason why the particles do not in- 
crease in number in direct proportion to the amount of the pollution, 
which is this, — with the increase in the size of the city there is not 
VOL. XVII. 21/6/90 
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