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Show 330 C. MAGONO and C. W. LEE diameter, in the usual sense. Snow crystals of cup or scroll type are frequently observed in frost and in artificial snow crystals. However, the snow crystals of these types are hardly ever observed in natural snow. The Cloud Physics Group of Hokkaido University took about 30,000 microscopic photographs of natural snow crystals during the recent 10 years, but no cup type crystals were found. 3.4 Supplement of plane crystals with extensions of different forms Plane crystals with extensions of forms different from the center part indicate that the crystals suffered a change in temperature and humidity during their fall. Therefore such a change in form of branches is an important indicator from a meteorological point of view. In the present classification, the changes in the crystal form; from dendrite to sectors, from dendrites to plates are noted and a group was supplied as seen in P2 of Table 1. 3.5 Crystals with an irregular number of branches In Nakaya's classification, snow crystals of plane type were classified in detail, however two- branched, three- branched, four- branched and twelve-branched crystals are assumed to be formed under the same meteorological conditions, because they commonly have two center nuclei and their differences in the numbers of branches are only due to the accidental manner of the distribution of branches to the two center nuclei. 3.6 Detailed classification of snow crystals of spatial types When snow crystals of plane type pass through a cold air layer around - 20bC, spatial extensions develop on their basal plane, although the reason is not understood. Because this phenomenon usually occurs when plane snow crystals fall through a temperature inversion layer, the snow crystals of this type are very important as an indicator of the existence of a temperature inversion layer. It is also possible to estimate the height of the inversion from the type of branches of the snow crystals of this type. . In the present classification, snow crystals of - this type were classified into four groups, considering the forms of both branches and basal planes, as seen in P6 of Table 1. Snow crystals of radiating type were also divided into two groups from the same point of view, as seen in P7 of Table 1. The snow crystals of radiating type are assumed to originate near - 20° C. 3.7 Supplement of snow crystals with spatial extensions at the ends Nakaya classified this combination of columns and plane crystals as one |