Abstract
The droplets of cloud on mountains and those of fog in urban area were captured, and the form, nature and size of their nuclei were studied by using an electron-microscope and a chamber of constant humidity. These nuclei are of the same form and nature as the hygroscopic particles in haze and the combustion products artificially produced. No sea-salt nuclei were found in our observations, and therefore the sea-spray appears to be insignificant as the source of condensation nucleus. It is supposed that cloud and fog nuclei are composed of combustion products, which are the mixture of hygroscopic and nonhygroscopic substances. It was also found that the hygroscopic substance is not pure sulphuric acid.
