1889-90.] 
Mr J. Aitken on Bust Particles. 
193 
On the Number of Dust Particles in the Atmosphere of 
certain Places in Great Britain and on the Continent, 
with Remarks on the Relation between the Amount 
of Dust and Meteorological Phenomena. By John 
Aitken, F.R.S. (With 3 Plates). 
(Read February 3, 1890.) 
The portable dust-counting apparatus described in a previous 
communication to this Society* was designed with a view of making 
observations on the air at situations where it would be inconvenient 
to work with the larger laboratory apparatus ; and also to enable 
these observations to be made under conditions more favourable for 
avoiding local impurities than is possible when working in a house. 
As the construction of this portable apparatus was completed just 
as I was about to start for the Continent, the opportunity seemed a 
favourable one for continuing the investigation into the number of 
dust particles in the atmosphere, and extending our knowledge on 
the subject in other countries. The portable apparatus is reduced 
to such dimensions that it adds but little to one’s personal 
luggage, and can be easily carried to the place where the observations 
are to be made. 
This new form of apparatus has been found to do its work 
satisfactorily. If a new set of apparatus were made, the only altera- 
tions the past experience would suggest is to omit the smallest 
of the stopcock measures, because I have never as yet had 
occasion to measure outside air so full of particles that the testing 
could not have been done with the second smallest measure. The 
smallest measure should therefore be only retained if the apparatus 
is required to test air extremely full of particles. For air of 
the country comparatively free from pollution, all the stopcock 
measures may be omitted, as they are never required. When the 
air is pure large quantities of it require to be sent into the 
receiver, and the air-pump alone is used. When the air is fairly 
pure, such as country air, 5 or 10 c.c. are generally required for each 
test. 
The silver counting stage of the apparatus was at one time found 
* Proc. Boy. Soc. Edin ., vol. xvi. 
VOL. XVII. 7/8/90 
N 
