, or which can exist. Mountain ranges and currents of
air of unequal temperatures may produce visible vapour, but not true cloud.

_Cumulus._ This cloud is always formed at "the dew point." The vapour of
the lower atmosphere, at this elevation, is condensed, or rendered visible.
In fog the dew point is at the surface of the earth; in summer it may be
several thousands of feet above. The Cumulus cloud forms from below. The
invisible vapour of the lower atmosphere is condensed, parts with its
thousand degrees of latent heat, which rush upwards, forcing the vapour
into the vast hemispherical heaps of snowy, glittering clouds, which, seen
in midday, appear huge mountains of clouds; the "cloud-land" of the poet,
floating in liquid air. The Cumulus cloud is ever changing in form.
Cumulating from a level base, the top is mounting higher and higher, until
the excessive moisture is precipitated in heavy rain, hail, or thunder
showers.

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