Instrument for measuring particulates in a fixed volume of air, 1918.
© Science Museum / Science & Society Picture Library
Diagram taken from the 'Quarterly Journal of the Royal Meteorological Society', (1918). Dr J S Owens used an arrangement like this to draw a fixed volume of air through the filter paper at the top, by syphoning a fixed volume of air from the flask below. The shade of dirt deposited could then be compared with a standard scale.