7. The Account of Clouds that are

Thus much, then, of the skies that used to be, and clouds “more lovely than the unclouded sky,” and of the temper of their observers. I pass to the account of clouds that are, and—I say it with sorrow—of the distemper of their observers.

But the general division which I have instituted between bad-weather and fair-weather clouds must be more carefully carried out in the sub-species, before we can reason of it farther: and before we begin talk either of the sub-genera and sub-species, or super-genera and super-species of cloud, perhaps we had better define what every cloud is, and must be, to begin with.

Every cloud that can be, is thus primarily definable: “Visible vapour of water floating at a certain height in the air.” The second clause of this definition, you see, at once implies that there is such a thing as visible vapour of water which does not float at a certain height in the air. You are all familiar with one extremely cognizable variety of that sort of vapour—London Particular; but that especial blessing of metropolitan society is only a strongly-developed and highly-seasoned condition of a form of watery vapour which exists just as generally and widely at the bottom of the air, as the clouds do—on what, for convenience’ sake, we may call the top of it;—only as yet, thanks to the sagacity of scientific men, we have got no general name for the bottom cloud, though the whole question of cloud nature begins in this broad fact, that you have one kind of vapour that lies to a certain depth on the ground, and another that floats at a certain height in the sky. Perfectly definite, in both cases, the surface level of the earthly vapour, and the roof level of the heavenly vapour, are each of them drawn within the depth of a fathom. Under their line, drawn for the day and for the hour, the clouds will not stoop, and above theirs, the mists will not rise. Each in their own region, high or deep, may expatiate at their pleasure; within that, they climb, or decline,—within that they congeal or melt away; but below their assigned horizon the surges of the cloud sea may not sink, and the floods of the mist lagoon may not be swollen.