On the radioactivity of atmospheric precipitates

The radioactivity of the atmospheric precipitates (snow and rain) was determined in 33 cases. It was found that snow usually has a greater activity than rain; that rain in thunder-showers is more active than ordinary rain; and that at least a certain amount of activity is acquired by precipitates during their fall from the clouds to the ground level. It was also possible to ascertain the presence of decay products of thoron in precipitates.