Cloud Photography
According to Arthur J. Weed, Chief Instrument Maker, U. S. Weather Bureau, the first requisite for cloud photography is a good camera with a rigid support. To this equipment a ray filter to shut out the excess of actinic rays from the blue sky is added. The filter, consisting of colored screens vary-
Ellerman, photo.
Nimbus, with fog or stratus hovering in the valleys, Mount Wilson, Cal.
ing from yellow to red, is usually necessary, inasmuch as the exposure required for the cloud results in an over exposed sky. Very dense clouds may be photographed without the use of a ray filter. Cirrus clouds, however, require a strongly-colored ray filter. A black mirror answers the purpose of a ray filter and, in certain cases, gives a better negative. The details of cloud photography are described in the Monthly Weather Review, August, 1920.
