The water drops falling in a stagnant air were investigated with a stroboscopic camera, and the following results were obtained. (1) The water drops with their fall velocities larger than 8m/sec were frequently observed. (2) The surface tension of a dilute solution of silver chloride of 0.01 percent, which was used to make the shape of water drops clear, was found to be the same as that of pure water within the scope of experimental error. (3) The shapes of falling drops of various sizes were photographed, and it was found that these drops vibrated vertically, even after they had fallen down the distance of 12 meters, and the grade of the drcp deformation was dicussed. (4) It was sometimes observed that on the surface of a water drop a horizontal stripe or rumple appeared. This is considered to be a shock wave on the drop surface, and to be related to the separation phenomena.
The shape and fall velocity of raindrops were observed by means of the photographs taken with a dark-field by electric sparks at 100 times/sec. 62 successful photographs of raindrops were obtained. Various waterdrops of known mass were taken in photograph after llm fall in the state of still air, and the relation among the mass, fall velocity and deformation were observed. Raindrops and waterdrops were compared with each other in shape and fall velocity. In the state of still air, the shapes and fall velocities of raindrops and waterdrops were similar. The maximum fall velocity was 980cm/sec, and the largest diameter was 0.51cm. The drag coefficient of raindrop is discussed on the basis of these data.
The shadow photograph method was applied to obtain a record of the form, size and mass of snow crystals. The apparatue for this method is very simple and is shown in Fig. 1. Illuminating the glass plate G, on which many snow crystals were received, from above with a small electric torch bulb L for a few seconds, the shadow of crystals is taken directly as a shadow photograph on the photographic paper in the cassette C. Such a shadow photograph is a record of the form and size of snow crystals on the glass. By heating the glass plate mildly, the individual snow crystals are melted into hemispherical droplets. A shadow photograph of these droplets is taken in the same way as above, and gives a record of the mass of the original crystals. By this method, about fifty pairs of records for various kinds of snow crystal shapes were obtained on Mt. Taisetsu in Hokkaidô, in February 1953. The relation between the mass and the dimension of snow crystals was sought from these records. Excepting the case of plane dendritic crystals, the results coincide fairly well with the results of the empirical formulas obtained by Nakaya and Terada. And on this occasion, the empirical formulas for stellar and columnar crystals are newly obtained.