Diurnal variation of intermediate and large ions of the atmosphere at Washington, D.C.

Continuous records of the intermediate‐ion and the large‐ion contents of the atmosphere at Washington, D.C., were secured for identical samples of air, during the latter part of May and the first half of June 1933. The results reveal diurnal variations in the two sets of ions that are similar in character. The most prominent features of each is a pronounced maximum centering on about 21h, local time. For the 12‐hour interval, from 4h to 16h, both ion‐contents are low and undergo but minor variations. The variation in the number of intermediate ions from day to day is proportional to the variation in the number of large ions present, but the variation is correspondingly less during times of the higher than during times of the lower large‐ion content of the atmosphere. Intermediate ions are generally numerous during times of thunderstorms, not as a consequence of the Lenard effect, as surmised by Schachl, but probably because of the increased number of small ions present at such times. The increase in number of small ions is apparently due, according to previous results, to radioactive matter carried down by the rain after having been carried upwards from the Earth's surface through convection‐currents during the formation of the thunderstorm. Without further investigational work, the full significance of the similarity in character of the diurnal‐variation curves for intermediate and large ions is not fully apparent, but it appears that particles are coming into the atmosphere, assorted into two definite sizes, from a common source.