The tops of the Cumulus, carried away by the upper equatorial currents, form the Cirrus clouds, which clouds must be frozen vapour, as they are generally from twenty to thirty thousand feet above the level of the sea. The base of the Cumulus is probably never more, in England, than five thousand feet high, rarely this. The _Nimbus_ is the _Cumulus_ shedding its vapour in rain; and the _Stratus_ is the partially exhausted and fading Nimbus. Poets in all ages have watched the clouds with interest; and Shakspeare has not only correctly described them, but has, in metaphor, used them in some of his sublimest passages. Ariel will "ride on the curled clouds" to Prospero's "strong bidding task" that is, ride on the highest Cirrus cloud, in regions impassable to man. How admirably the raining Cumulus (Nimbus cloud) is described in the same play: "_Trinculo._ Here's neither bush[4] nor shrub, to bear off any weather at all, and another storm brewing. I hear it sing i' the wind: yond' same black cloud, yond' huge one, looks like a foul[5] bumbard that would shed his liquor ... ... Yond' same cloud cannot choose but fall by pailfuls." Hamlet points to a changing Cumulus cloud, when he says to Polonius, "Do you see that cloud, that almost in shape like a camel?" "_Pol._ By the mass, and 'tis like a camel, indeed. _Ham._ Methinks it is like a weasel. _Pol._ It is back'd like a weasel. _Ham._ Or like a whale? _Pol._ Very like a whale." But the finest cloud passage in the whole range of literature is contained in _Antony and Cleopatra_, painting, as it does, the fallen and wasting state of the emperor (Act IV. Sc. 12.): "_Ant._ Eros, thou yet behold'st me? _Eros._ Ay, noble lord! _Ant._ Sometime we see a cloud that's dragonish: A vapour, sometime, like a bear, or lion, A tower'd citadel, a pendant rock, A forked mountain, or blue promontory With trees upon't, that nod unto the world, And mock our eyes with air. Thou hast seen these signs: They are black vesper's pageants. _Eros._ Ay, my lord. _Ant._ That which is now a horse, even with a thought, The rack dislimns; and makes it indistinct, As water is in water. _Eros._ It does, my lord. _Ant._ My good knave, Eros, now thy captain is Even such a body: here I am Antony; Yet cannot hold this visible shape, my knave."