Plate 28.
HIGH TURRETED CLOUD.
(Alto-cumulus Castellatus.)
Plate 28.
HIGH TURRETED CLOUD.
(Alto-cumulus Castellatus.)
Another form of almost equal beauty is shown in Plate [29]. The rounded balls make their appearance as semi-transparent spots upon the sky, and in their general characters might easily be mistaken for cirro-macula. But a few minutes will be enough to decide the question. The little spots rapidly grow denser, frequently becoming ragged at the edges; they never drop down the slender filaments which usually descend from cirro-macula, and their edges are never denser than their central parts, which, it will be remembered, was a frequent feature of the true speckle cloud. The cloudlets are obviously rounded balls arranged in patches, which may turn gradually into alto-stratus by their fusion, or, after an existence of minutes or hours, the whole may disappear by a disintegration of each ball, by its breaking up into a ragged mass and melting away. The altitude at which this cloud forms is between 5000 and 9000 metres, according to measurements made by the writer, the actual specimen figured being about 7000. It is almost as characteristic of thunder weather as the last, but whereas Plate [28] shows a variety which is most often seen before 3 p.m., since it only occurs while the cloud planes are rapidly rising, the one before us may be formed at almost any time of day, but most frequently occurs in the afternoon. An imperfect form of it is frequently met with about sunset, in which the rounded balls are not usually so well defined as when the sun is high above the horizon. Alto-cumulus glomeratus would be a suitably descriptive name.