The history of condensation nucleus counters

Condensation of supersaturated vapors has been used for more than a century to grow small aerosol particles to sizes that can be detected optically. This paper discusses the history of instruments that use condensation to detect particles. I divide this history into two main sections. The first of these focuses on the development of expansion-type instruments including the "dust counters" in which John Aitken played the decisive role and "photoelectric nucleus counters" primarily by L. W. Pollak and coworkers. The second section deals with the development of steady-flow condensation nucleus counters (CNCs) in which Jean Bricard and coworkers played the decisive role. The importance of calibration methodologies is also pointed out. Refinements by instrumentation manufacturers and many aerosol scientists have led to the reliable, accurate instruments that are widely used today.