(Cirro-macula.)
Plate 23.
SPECKLE CLOUD (Ley).
(Cirro-macula.)
Cirro-macula frequently gives rise to the fibrous form of cirrus we have called cirrus caudatus. The granules of the cirro-macula grow denser, and begin to drop their frozen particles as soon as they become large enough. Indeed, a cloudlet of cirro-macula may sometimes be seen to turn bodily into a fine line of falling crystals, which will be a curving line of cirrus. On the other hand, it will sometimes remain visible for an hour or more without any trace of descending streaks or floating fibres. Pure cirro-macula such as Plate [23] is not often seen; it is far more frequently mixed with more solid-looking cloudlets and descending fibres, such as are shown in Plate [24], which gives the same point of view as 23, but a quarter of an hour later, and photographed with a longer focus lens. These two photographs, together with 20 and 21, give excellent examples of the use of the black mirror. In none of the four could the naked eye detect all of the cloud structures. The whole sky was a blaze of dazzling light, but by adjusting exposure and development the details are fully brought out without the least difficulty.
Plate 24.
CIRRUS CAUDATUS AND CIRRO-MACULA.