Abstract
Some special considerations should be necessary for the method. of measurement of very low concentrations, such as the global background values of submicron aerosols. We have added some improvements to a Pollak-type condensation nucleus counter for this purpose (Figs.1-3). Though the Pollak-type counter is very practical for daily observation, it is not sufficient for the purpose of the long-term comparison of data, because it is, as is well known, a relative instrument. Therefore it is necessary to have another instrument of an absolute counting type, such as an Aitken-type condensation nucleus counter. A photographic recording Aitken-type counter has been developed for the purpose (Figs.4-6).
