phere is almost or altogether cloudless; and, when formed in the early part of the night, it may melt away under a gathering close cloud before the morning. It often presents most beautiful assemblages of specular crystals on the ground, and sometimes makes superb deposits on the sides of trees and walls against which it is drifted; and, though usually disliked by farmers and gardeners for the injury it inflicts on ripening crops and on opening blossoms, it constitutes, on the whole, a beneficent provision for protecting plants from the severity of keen frosts.

A haze in the air is vapour obscurely visible, and may frequently be observed brooding over the face of waters, or over the face of moist lands, at times when a hot sunshine from an unclouded sky is producing rapid evaporation. A fog or mist, in all ordinary instances, is merely vapour completely visible, or a cloud resting at the bottom of the atmosphere. But a thick driving fog is generally very electric; and a stagnant fog in a great city has sometimes a dense intermixture of smoke, and is sometimes a curious compound of vapour, hoar-frost, smoke, and dust. London fogs are notoriously dense and dismal; and one which lasted six days in the winter of 1814, not only, like many others, occasioned a necessity for artificial lights through all the day-time, but congealed itself on walls and railings, and made a frozen deposit beneath the trees of St James' Park to the depth of an inch. So awful is the gloom of the worst fogs in London, Glasgow, Amsterdam, and some other populous cities, so oppressive to the feelings of the sensitive, and so obstructive to the business of the active-that the words might almost be applied to them which Byron penned

in description of an imaginary darkening of the uni

verse

"The bright sun was extinguish'd, and the stars Did wander, darkling in the eternal space,

Rayless and pathless; and the icy earth

Swung blind and blackening in the moonless air.
Morn came, and went, and came, and brought no day.
And men forgot their passions in the dread

Of this their desolation; and all hearts

Were chill'd into a selfish prayer for light."

What is called a dry fog, however, is greatly worse than the fogs of cities, and probably arises from a diversity of causes, and has a corresponding diversity of nature. It does not always make the air murky, but oftener gives it a muddy hue, and causes the sun and moon to look like blood; nor does it always maintain a still and suffocating character, but frequently has all the accompaniments of both electric outburst and volcanic convulsion; and it commonly extends over great tracts, and has been known to affect so much as one-fourth of the world. In the summer of 1783, a dry fog prevailed during four weeks over all Europe, and passed on to the centre of Asia, and struck such terror into millions, that they abandoned their occupations, and imagined the end of all things to be at hand. The air was thick, and of the colour of rust; the electric fluid produced intense sultriness, and played away in frequent and destructive thunderstorms; hail-showers, hurricanes, and floods strewed some districts with desolation; and earthquakes and volcanic eruptions shook large portions of both the north and the south of Europe. Some fogs also have a luminous appearance, and are supposed to be mag

netic; and a peculiar fog broods over the Polar Seas on the approach of winter, and bears the expressive name of frost-smoke.

Clouds are not so diversified in nature as fogs, but possess wondrous diversity of size, form, colour, and evolution. They look like the drapery of the sky, and exhibit the most glorious beauty. The aerial scenery which they form, conjointly with the azure above them, and the lights and shades below them, has often incomparably more power and gorgeousness than the most brilliant landscapes of sea, and dale, and mountain; and, by being ever shifting, ever various, and ever new, it combines the witchery of a camera-obscura with the graces of a fixed picture. The clouds are also an awning to the earth, and a pavilion to the sunshine; and they possess the most sublime associations with the poetry of all time, and with the imagery of the sacred oracles. The Saviour of men was received into heaven in a cloud, and will come again in the clouds of heaven.

The densest clouds sometimes float so low as to touch the tops of trees and steeples; and the thinnest and lightest often rise so high as from three to five miles. Some are the smallest perceptible masses of visible vapour; and others have a thickness of many hundred feet, and a superficies of from twelve to twenty square miles. But most in our latitudes have both a medium height and a medium size. The curl-clouds, or those which look like locks of hair, are the highest. The stacken-cloud, or cumulus, of dense structure and either convex or conical form, floats near the ground, yet often rises with the advance of day, and sinks with its decline, and sometimes swells outward and upward

in bulk, till it resembles a stupendous mountain, or range of mountains, clad in snow. The fall-cloud, or stratus, is a level sheet-like expanse, increasing from beneath; and it commonly forms in the calm of the evening from an evolution of vapour immediately over lake or valley, and glides slowly up the neighbouring ascents, to brood over the tops of the hills. The fleecycloud is an aggregation of small roundish masses, fleeting in winter, playful in summer, floating at great varieties of height, and often adorned with the gayest gems of colour. The wane-cloud is a medium thing between the curl-cloud and the fall-cloud, but frequently changes its form, and at one time bursts into rain, at another soars away to a high altitude. Other clouds and there are many others are variations or combinations of these; and all the clouds, except the black ones, which are just discharging themselves in rain, and the piled and fiery ones, which are full of electricity, pass by many degrees of transmutation into one another, and effect their grandest feats of scenery by the number, and novelty, and variety of their neverceasing mutual changes.

Rains have every variety of character, from the slightest perceptible drizzle to the most deluging thunder-plumps, from the smallest visible globules to drops of nearly half an inch in diameter, and from a mere momentary sprinkling to continuous wide-spread falls for months. The annual quantity is greatest in the regions of greatest evaporation, and therefore greater in the tropics than in the temperate zones, and greater in the temperate zones than toward the poles. But comparatively great quantities are often precipitated in comparatively small periods. The rains of the tropics

are about six times heavier than those of central Europe, and sometimes fall like water-spouts, or like lakes from the sky; and they also occur mainly, or almost solely, at one season of the year, and are then so constant or prolonged, as to constitute the characteristic feature of the tropical winter. Even the rains of some places in Britain yield much larger aggregate quantities than those of others, and yet fall in far fewer days. Most of the rains of cool countries are fitful and local, and many are either much modified or wholly determined by the relative positions of land and sea, and of mountains and plains; but some are of such enormous extent as to fall simultaneously over many hundreds of miles. The drops of most showers vary in diameter from the twenty-fifth of an inch to a quarter of an inch, but are commonly large or small, according to the height from which they come; and the monster ones which commence some thunder-plumps, and form marks as large as shillings, all descend from very lofty elevations.

Rains do not consist simply of water, but contain various though minute proportions of other substances, particularly gases and organic products and volatile matters, which serve as nourishment to plants. Indeed, they are the scavengers of the atmosphere, and sweep out of it all undue accumulations of its foreign admixtures; and, in this capacity, they sometimes have extraordinary and very curious work to do. Substances of striking colour and singular appearance are occasionally sent high into the air by conflagrations, tempests, whirlwinds, and volcanic eruptions, and when brought back to the ground, either by rain or in company with it, make awful and horrific showers. Even