Plate 27.
FLAT ALTO-CUMULUS.
(Alto-cumulus Stratiformis.)
Plate 27.
FLAT ALTO-CUMULUS.
(Alto-cumulus Stratiformis.)
We now come, in Plate [28], to a cloud of singular beauty. It forms rapidly in a clear sky, its first traces bearing a striking resemblance to cirro-macula, but the floccules, instead of remaining semi-transparent or dropping cirrus threads, rapidly become opaque balls of cloud which lengthen upwards. This upward tendency causes the formed cloudlets to have their longer axes vertical, which is very characteristic. It might be named alto-cumulus castellatus, or high-turreted cloud. Mr. Ley named it stratus castellatus, or turret-cloud, but it certainly belongs to the cumulus section of the alto group. Thunder weather is the invariable condition for its production. If it is seen, at least in England, thunderstorms are certain to be recorded not very far away. When this particular photograph was being taken in South Devon, very destructive storms were recorded in Brittany and in the English Midlands, and the anvil-shaped tops of unmistakable thunder-clouds were visible above the horizon while the exposure was being made.
