§ 1. From the tenor of the foregoing chapter, the reader will, I hope, be prepared to find me, though dogmatic (it is said) upon some occasions, anything rather than dogmatic respecting clouds. I will assume nothing concerning them, beyond the simple fact, that as a floating sediment forms in a saturated liquid, vapour forms in the body of the air; and all that I want the reader to be clear about, in the outset, is that this vapour floats in and with the wind (as, if you throw any thick colouring-matter into a river, it floats with the stream), and that it is not blown before a denser volume of the wind, as a fleece of wool would be.

§ 2. At whatever height they form, clouds may be broadly considered as of two species only, massive and striated. I cannot find a better word than massive, though it is not a good one, for I mean it only to signify a fleecy arrangement in which no lines are visible. The fleece may be so bright as to look like flying thistle-down, or so diffused as to show no visible outline at all. Still if it is all of one common texture, like a handful of wool, or a wreath of smoke, I call it massive.

On the other hand, if divided by parallel lines, so as to look more or less like spun-glass, I call it striated.