John Aitken, "On improvements in the apparatus for counting the dust particles in the atmosphere." Proceedings of the Royal Society of Edinburgh, 1889: 16 (129) : 135–172.

Suggested by Douglas Craig

Dr. Aitken has devoted a vast amount of attention to the enumeration of dust-particles in the air, on the Continent as well as in Scotland, to determine the effects of their variation in number.

On his first visit to Hyères, in 1890, he counted with the instrument 12,000 dust-particles in a cubic inch of the air: whereas in the following year he counted 250,000. He observed, however, that where there was least dust, the air was very clear; whereas with the maximum of dust, there was a very thick haze.

Plate I. There are five distinct parts in the apparatus – (1) the test-receiver R; (2) the air-pump P; (3) the measuring apparatus M; (4) the illuminating arrangements L; and (5) the gasometer G.