John Aitken, FRS, FRSE LLD (18 September 1839 – 14 November 1919) was a Scottish meteorologist, physicist and marine engineer.

He was one of the founders of cloud physics and aerosol science, who built the first apparatus to measure the number of dust and fog particles in the atmosphere, a koniscope.

This work was documented in an article titled "On some nuclei of cloudy condensation", in the 39th volume of the Transactions of the Royal Society of Edinburgh published in 1898.

[9] John Aitken was the author of a number of important pioneering discoveries "On Dust, Fogs and Clouds" (the title of an 1880 article he penned).

Cargill Gilston Knott assembled and edited Aitkens works for the Royal Society of Edinburgh, and contributed an introductory Memoir:[13]