In experiments carried out near Sydney, supercooled water
clouds were " seeded " with ice crystals by dropping pellets of solid
carbon dioxide into them. Up to August
25, 1948, 20 experiments were made under conditions sufficiently
well defined for the experiments to be significant. In 15 of them precipitation
is believed to have been released artificially. Of 11 clouds with tops colder
than -7�C., 10
precipitated. The depth of the treated clouds ranged from 1000 to 15,000 ft.
In none of these did natural precipitation
occur within 20 miles. Further evidence that the effect is genuine is given by
the fact that both the likelihood of success in inducing precipitation and the
time between treatment of the cloud and the appearance of precipitation at its
base, varied consistently with the cloud characteristics.
The observations are consistent with the
view, as postulated by Bergeron, that the precipitation grew from ice crystals
(formed by the dry ice pellets).