Aitken's pocket dust counter, 1890.
© Science Museum / Science & Society Picture Library
Plate taken from 'Proceedings of the Royal Society of Edinburgh' (1890). Dr John Aitken (1839-1919) was responsible for initiating the scientific measurement of particulates in the air. In this paper to the Royal Society of Edinburgh, he described the smallest of three devices he invented to count dust. The largest was installed in the observatory on the top of Ben Nevis in Scotland; this one was the 'size of a well-filled cigar case'. A piston action drew air into the device's test chamber, which was full of supersaturated air. The dust in the test sample formed nuclei for the water in the chamber to coalesce around, forming drops that could then be counted.