claws or arms of some great monster crab or polypus. Bigger and bigger the threatening mass swelled, and the evil-looking arms stretched half round the horizon to the zenith, as if the monster was about to enclose the whole world in its grasp—a wonderful and awful appearance. Our sails flapped as we rolled in the calm; we lowered the mainsail, made all snug, and awaited. First, constant and vivid sheet and forked lightning of a blue colour came out of the cloud, and then down burst the squall on us, and such a squall. The cloud had enveloped all the sky, had blotted out all the stars; never have I experienced so complete a darkness on the seas. The wind blew with great fury; and we could not turn our faces to the stinging rain, so smartly it struck. "We scudded on before the heavy gusts."
The modern explanation of rocky cloud is very simple. Under certain circumstances air seems to rise in columns, when it is chilled, both by its own expansion and by its projection into the colder regions of the atmosphere. At some height a temperature will be reached when the vapour in the air is condensed. This level gives the line of the flat base of the cloud, while the rocky summits are formed by the air rushing up like the steam out of the funnel of a locomotive. Rocky clouds are in fact the visible capital of an invisible column of air.
The form and details depend on circumstances. On a fine day evaporation produces a beautiful, quiet, and peaceable looking cloud, while the rolling eddies in front of a thunderstorm produce wild-looking masses of extraordinary shape, whose terrifying effect is enhanced by their inky look and by the ominous calm which precede an impending storm.
Here is a diagram to show the general idea of the origin of rocky cloud where the dotted lines below indicate the position of the rising air column under the rocky cloud.
Sometimes a column of rising air gets attenuated into a thread, and when this condenses we get a hairy or fibrous cloud. This I have endeavoured to show in the upper part of the diagram.
There are numerous forms of hairy structure which we cannot at present explain, but they are all unquestionably only forms of condensed vapour drawn out into threads and fibres, as vfe so often see
