Note 42 — Chapter V · NITROGEN AND AIR
George Kamensky translation
Their presence in the air is naturally due to the diffusion of germs into the atmosphere, and owing to their microscopical dimensions, they, as it were, hang in the air in virtue of their large surfaces compared to their weight. In Paris the amount of dust suspended in the air equals from 6 (after rain) to 23 grams per 1,000 c.m. of air.