Microscopic Examination of Fog-, Cloud-and Rain-Droplets

Abstract

OF the many methods proposed hitherto for the measurement of the size and concentration of droplets in fogs and clouds, none can be considered as quite satisfactory. The extensively used method of diffraction rings (corona) can be applied only in the relatively rare case of isodisperse fogs. The photographic method devised by Findeisen¹ is rather complicated, and can scarcely be used in field work. The direct measurement of the droplets collected on greased wires or on glass slides is hampered by very rapid evaporation of the droplets and distortion of their spherical shape. The method proposed recently by Hagemann², namely, collecting the droplets on a thin layer of castor oil and photographing them during their fall through the layer, has many disadvantages and can be used only for droplets with a radius less than 5.