The electron, its isolation and measurement and the determination of some of its properties

by Robert Andrews Millikan

. To obtain

he proceeded exactly as Townsend had done in letting the ions condense droplets of water about them and weighing the cloud thus formed.

Fig. 1

But in order to form the cloud, Thomson utilized C. T. R. Wilson’s discovery just touched upon above, that a sudden expansion and consequent cooling of the air in

([Fig. 1]) would cause the ions in