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Show 328 C. MAGONO and C. W. LEE Several years ago, the authors undertook to improve Nakaya's classification method with his agreement, and recently they arrived at a fairly satisfactory meteorological classification method by several modifications and supplements of his classification. The authors undertook to determine also the temperature and humidity conditions for the formation of various kinds of natural snow crystals by the use of purely meteorological methods. The conditions will be described later. One will find that the conditions are quite similar to Nakaya's Ta- s diagram. 2. General classification of natural snow crystals from a meteorological point of view In order to remove the inconvenience in the description of the type of natural snow crystals, some parts of Nakaya's classification were modified and some classifications were added according to the result of laboratory experiments described above and the result of meteorological observation. Thus the number of classification increased from 36 to 80 classes which is listed in Table 1. In the table, the corresponding numbers of plates of microscopic photographs are shown at the right end. And the shape of snow crystals of each class are shown schematically in Fig. 1, and illustrated by microscopic photographs at the end of this paper. The modifications and supplements for Nakaya's classification are explained below. 3. Modifications and supplements In order to remove the inconvenience in the description of the type of natural snow crystals, the following modifications and supplements were made. 3.1 Supplement of sheath type crystals There are microscopically three kinds of needlelike snow crystals, although they visually seem to belong to the same kind. The first is the needlelike crystal with knife edge shape tops, the second is the extremely thin hollow column, and the last is the extremely thin solid column. The first was classified as " needle crystals" by Nakaya, but the second was not clearly classified. However, the snow crystals of the second type were shown in the results of laboratory experiment by Hallett and Mason, Kobayashi, and Nakaya, Hanajima and Muguruma, and were observed in natural snow crystals as reported by Magono and his colleagues11). There- |