Oft when the wintry storm had ceased to rave,
He roamed the snowy waste at even, to view
The clouds stupendous, from the Atlantic wave

High lowering, sail along the horizon blue;
Where, 'midst the changeful scenery, ever new,
Fancy a thousand wondrous forms descries,
More wildly great, than ever pencil drew;

Rocks, torrents, gulfs, and shapes of giant size,
And glitt❜ring cliffs on cliffs and fiery ramparts rise.

Minstrel.

Clouds," says Dr. Thompson, are not formed in all parts of the horizon at once; the formation begins in one particular spot, while the rest of the air remains clear as before; and though the greatest quan

tity of vapour exists in the lower strata of the atmosphere, clouds

never begin to form there, but always at some considerable height." It is remarkable, says the same author, that the part of the atmosphere at which they form has not arrived at the point of extreme moisture, nor near that point, even a moment before their formation.

They are not formed, then, because a greater quantity of vapour has got into the air than could remain there without passing its maximum. It is still more remarkable, that when clouds are formed, the temperature of the spot does not always suffer a diminution, although this may sometimes be the case. On the contrary, the heat of the clouds themselves is sometimes greater than that of the surrounding air. Neither, then, is the formation of the clouds owing to the capa city of air for combining with moisture being lessened by cold. So far from this being the case, we often see clouds, which had remained in the atmosphere during the heat of the day, disappear in the night, after the heat of the air was diminished.

The formation of clouds and rain, then, cannot be accounted for by the principles with which we are acquainted. It is neither to the saturation of the atmosphere, nor the diminution of heat, nor the mixture of airs of different temperatures, as Dr. Hutton supposed; for clouds are often formed without any wind at all either above or below them and even if this mixture constantly took place, the precipitation, instead of accounting for rain, would be almost imperceptible.

It is a well-known fact, that evaporation goes on for a month or two together in hot weather without any rain. This sometimes happens in the temperate zone; and every year in the torrid zone. At Calcutta, during the month of January, in the year 1785, it never rained at all: the mean of the thermometer for the whole month was 66 degrees: there were no high winds, and, during the greater part of the month, scarcely any wind at all.

As the moisture which is thus raised by evaporation is not accumulated in the atmosphere, above the place from which it was evaporated, it must be disposed of in some other way; but the manner in which this is accomplished is not so well known. If it be carried on daily through the different strata of the atmosphere, and wafted to other regions by superior currents of air, it is impossible to account for the different electrical states of the clouds, situated between different strata, which often produce the most violent thunder storms.

For vapours are conductors of the electric fluid, and, of course, would daily restore the equilibrium of the whole atmosphere through which they passed. There would, therefore, be no positive and negative clouds, and consequently no thunder storms. Clouds could not have remained in the lower strata of the atmosphere and been daily carried off by winds to other countries; for there are often no winds at all, during several days, to perform this office; nor would the dews diminish as they are found to do when the dry weather continues for a long time.

It is impossible for us to account for this remarkable fact upon any principle with which we are acquainted. The water can neither remain in the atmosphere, nor pass through it in the state of vapour. It must, therefore, assume some other form; but what that form is, or how it assumes it, we do not know.

- In order to render the study of meteorology more systematic, Mr. Luke Haward has lately introduced a scientific nomenclator for distinguishing the various forms or modifications of clouds, which promises to be of great use in this important, but hitherto neglected, branch of physical science.

The simple forms, or modifications, are three in number, and named, Cirrus, Cumulus, and Stratus. These are defined by Mr. Haward as follows:-The Cirrus is composed of parallel, flexuous, or diverging fibres, extensible in any or in all directions.

The Cumulus, convex or conical, heaps, increasing upwards from a horizontal base.

The Stratus, is a widely extended, continuous, horizontal sheet, increasing from below.

The intermediate modifications are four in number, each of which is formed from various combinations of the simple modifications just mentioned. They are the Cirro-cumulus, the Cirro-stratus, the Cumulo-stratus, and the Cumulo-cirro-stratus, or Nimbus; and are defined as follows.

Cirro-cumulus. Small well-defined roundish masses, in close horizontal arrangement.

Cirro-stratus. Horizontal or slightly-inclined masses, bent downward, or undulated, separate, or in groups consisting of a number of small clouds.

Cumulo-stratus. The cirro-stratus blended with the cumulus, and either appearing intermixed with the heaps of the latter, or superadding a wide-spread structure to its base.

Cumulo-cirro-stratus. The rain cloud. A cloud, or system of clouds, from which rain is falling. It is a horizontal sheet, above which the cirrus spreads, while the cumulus enters it laterally, and from beneath.

OF THE CIRRUS.

Clouds in this modification appear to have the least density, the greatest elevation, and the greatest variety of extent and direction. They are the earliest appearance after serene weather. They are first indicated by a few threads pencilled, as it were, on the sky.

These increase in length, and new ones are in the mean time added. laterally. Often the first-formed threads serve as stems to support numerous branches, which in their turn give rise to others. modification is represented by the following figure.

This

The increase is sometimes perfectly indeterminate, at others it has a very decided direction. Thus the first few threads being formed, the remainder shall be propagated either in one, two, or more directions laterally, or obliquely upward or downward, the direction being often the same in a great number of clouds visible at the same time. o

Their duration is uncertain, varying from a few minutes after the first appearance to an extent of many hours. It is long when they appear alone and at great heights, and shorter when they are formed lower and in the vicinity of other clouds.

This modification, although in appearance almost motionless, is intimately connected with the variable motions of the atmosphere. Considering that clouds of this kind have long been deemed a prognostic of wind, it is extraordinary that the nature of this connection should not have been more studied, as the knowledge of it might have been productive of useful results.

In fair weather, with light variable breezes, the sky is seldom quite clear of small groups of the oblique cirrus, which frequently come on from the leeward, and the direction of their increase is to windward. Continued wet weather is attended with horizontal sheets of this cloud, which subside quickly and pass to the cirro

stratus.

quarter opposite to that from which the storm arises. Steady high winds are also preceded and attended by streaks running quite across the sky in the direction they blow in.

The relations of this modification with the state of the barometer, thermometer, hygrometer, and electrometer, have not yet been attended to.

OF THE CUMULUS.

Clouds in this modification are commonly of the most dense structure they are formed in the lower atmosphere, and move along with the current which is next the earth.

A small irregular spot first appears, and is, as it were, the nucleus on which they increase. The lower surface continues irregularly plane, while the upper rises into conical or hemispherical heaps; which may afterwards continue long nearly of the same bulk, or rapidly rise to mountains, as represented by the following figure,

In the former case they are usually numerous and near together, in the latter few and distant; but whether there are few or many, their bases always lie nearly in one horizontal plane, and their increase upward is somewhat proportionate to the extent of base, and nearly alike in many that appear at once.

Their appearance, increase, and disappearance, in fair weather, are often periodical, and keep pace with the temperature of the day. Thus they will begin to form some hours after sun-rise, arrive at their maximum in the hottest part of the afternoon, then go on dimi❤ nishing, and totally disperse about sun-set.

But in changable weather they partake of the vicissitudes of the atmosphere; sometimes evaporating almost as soon as formed, at others suddenly forming and as quickly passing to the compound modifications.

The cumulus of fair weather has a moderate elevation and extent, and a well defined rounded surface. Previous to rain it increases more rapidly, appears lower in the atmosphere, and with its surface full of loose fleeces or protuberances.

Independently of the beauty and magnificence it adds to the face of nature, the cumulus serves to screen the earth from the direct rays of the sun, by its multiplied reflections to diffuse, and, as it were, economise the light, and also to convey the product of evaporation to a distance from the place of its origin. The relations of the cumulus with the state of the barometer, &c. have not yet been sufficiently attended to.

The formation of large cumuli to leeward in a strong wind, indicates the approach of a calm with rain. When they do not disappear or subside about sun-set, but continue to rise, thunder is to be expected in the night.

Contrary to the last, which may be considered as belonging to the day, this is properly the cloud of night; the time of its first appearance being about sun-set. It comprehends all those creeping mists which in calm evenings ascend in spreading sheets (like an inundation of water) from the bottom of valleys and the surface of lakes, rivers, &c.

Its duration is frequently through the night.

On the return of the sun the level surface of this cloud begins to put on the appearance of cumulus, the whole at the same time separating from the ground. The continuity is next destroyed, and the cloud ascends and evaporates, or passes off with the appearance of the nascent cumulus.

This has been long experienced as a prognostic of fair weather, and indeed there is none more serene than that which is ushered in by it. The relation of the stratus to the state of the atmosphere as indicated by the barometer, &c. appears notwithstanding to have passed hitherto without much attention.

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