Microphotographs of Ice Crystal in the Air (abbreviated as ICA for shortness in the text) are taken. From the measurement of their prints the size of ICAs, their space density and their properties are studied. Also the axis ratios of hexagonal twin prisms are measured, auxiliary axis 2
a=53μ principal axis 2
c=83μ, and
c/a =1.6 being the results. For hexagonal plate crystals 2
a=100μ,
c= 31μ. The Mean mass of hexagonal twin prism is 0.141 x 10
-6 gr., and that of hexagonal plate crystal 0.135 x 10
-6 gr. Among ICAs which come down at the same time and place, there exists a peculiar propensity of taking almost the same shape. The adhesion phenomenon of one crystal to another is frequently observed at the place where a solid angle is formed.
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