OF THE CIRRO-CUMULUS.

The cirrus having continued for some time increasing or stationary, usually passes either to the cirro-cumulus or the cirro-stratus, at the same time descending to a lower station in the atmosphere.

The cirro-cumulus is formed from a cirrus, or from a number of small separate cirri, by the fibres collapsing as it were, and passing into small roundish masses, in which the texture of the cirrus is no longer discernible, although they still retain somewhat of the same relative arrangement, as exhibited by the following figure.

This change takes place either throughout the whole mass at once, or progressively from one extremity to the other. In either case, the same effect is produced on a number or adjacent cirri at the same time and in the same order. It appears in some instances to be accelerated by the approach of other clouds.

This modification forms a very beautiful sky, sometimes exhibiting. numerous distinct beds of these small connected clouds, floating at different altitudes.

The cirro-cumulus is frequent in summer, and is attendant on warm and dry weather. It is also occasionally and more sparingly seen in the intervals of showers, and in winter. The following passage is beautifully descriptive of the appearance of this modification by moonlight:

For yet above these wafted clouds are seen
(In a remoter sky, still more serene)
Others, detached in ranges through the air,
Spotless as snow, and countless as they're fair;
Scatter'd immensely wide from east to west,
The beauteous semblance of a flock at rest.
These to the raptur'd mind aloud proclaim
Their mighty shepherd's everlasting name.

BLOOMFIELD.

It may either evaporate or pass to the cirrus or cirro-stratus.

A

OF THE CIRRO-STRATUS.

This cloud appears to result from the subsidence of the fibres of the cirrus to a horizontal position, at the same time that they approach towards each other laterally. The form and relative position, when seen in the distance, frequently give the idea of shoals of fish. Yet in this, as in other instances, the structure must be attended to rather than the form, which varies much, presenting at other times the appearance of parallel bars, interwoven streaks like the grain of polished wood, &c. It is always thickest in the middle, or at one extremity, and extenuated towards the edge, as represented by the following figure.

The distinct appearance of a cirrus does not always precede the production of this and the last modification.

The cirro-stratus precedes wind and rain, the near or distant approach of which may sometimes be estimated from its greater or less abundance and permanence. It is almost always to be seen in the intervals of storms. Sometimes this and the cirro-cumulus appear together in the sky, and even alternate with each other in the same cloud, when the different evolutions which ensue are a curious spectacle, and a judgment may be formed of the weather likely to ensue by observing which modification prevails at last. The cirro-stratus is the modification which most frequently and completely exhibits the phenomena of the solar and lunar halo, and (as supposed from a few observations) the parhelion and paraselene also. Hence the reason of the prognostic for foul weather, commonly drawn from the appearance of the halo.

OF THE CUMULO-STRATUS.

The different modifications which have been just treated of sometimes gives place to each other, at other times two or more appear in

the same sky; but in this case the clouds in the same modification lie. mostly in the same plane of elevation, those which are more elevated appearing through the intervals of the lower, or the latter showing dark against the lighter ones above them. When the cumulus increases rapidly, a cirro-stratus is frequently seen to form around its summit, reposing thereon as on a mountain, while the former cloud continues discernible in some degree, through it.This state continues but a short time. The cirro-stratus speedily becomes denser and spreads, while the superior part of the cumulus extends itself and passes into it, the base continuing as before, and the convex protuberances changing their position till they present themselves laterally and downward. These are well represented by the following figure.

The cumulo-stratus chiefly affects a mean state of the atmosphere as to pressure and temperature; but in this respect, like the other modifications, it affords much room for future observation.

OF THE NIMBUS, OR CUMULO-CIRRO-STRATUS. Clouds in any one of the preceding modifications, at the same degree of elevation, or in two or more of them, at different elevations, may increase so as completely to obscure the sky, and at times put on an appearance of density which to the inexperienced observer indicates the speedy commencement of rain. It is nevertheless extremely probable, as well from attentive observation as from a consideration of the several modes of their production, that the clouds, while in any one of these states, do not at any time let fall rain.

Before this effect takes place they have been uniformly found to undergo a change, attended with appearances sufficiently remarkable to constitute a distinct modification, which is represented by the following figure, called the Nimbus, or Cumulo-cirro-stratus cloud.

In this figure a shower is represented as coming from behind an elevated point of land.

The nimbus, although in itself one of the least beautiful clouds, is yet now and then superbly decorated with its attendant the rainbow which can only be seen in perfection when backed by the widely extended uniform gloom of this modification.

The relations of rain, and of periodical showers more especially, with the varying temperature, density, and electricity of the atmosphere, will probably now obtain a fuller investigation, and with a better prospect of success, than heretofore.

MOTIONS OF THE EARTH.

'She from the West her silent course advances
With inoffensive pace, that spinning sleeps
On her soft axle; while she paces even,

And bears us soft with the smooth air along.

MILTON.

When we consider the apparent diurnal motion of all the celestial bodies, we cannot but recognise the existence of one general cause, which produces this appearance. But when we consider that these bodies are not only at different distances from the earth, but at different distances from each other, and that these distances are not always the same, we shall find it difficult to conceive that it is the same cause that produces this appearance on all of them.

The difficulty, however, becomes considerably less when it is recollected, that a person in motion, looking at an object at rest, perceives the same change of position in the object as if he were himself at rest, and the object in motion in the opposite direction. Every one who has looked, for the first time, from the window of a carriage moving quickly along the road; or from the deck of a ship sailing smoothly along the shore; fancies that every thing which the carriage or vessel passes is in motion, and that he is himself at rest.

An appearance still more deceiving takes place, when a person looks out of the cabin window of a ship, in a dark night, at a distant light apparently in motion. For the change of place in the light may arise either from its being really in motion, or on board of another vessel, while the vessel in which the spectator is placed is at anchor; or the light may be stationary, and its apparent motion occasioned by the motion of the ship which carries the spectator; or it may even be occasioned by the motion of the vessel which carries the light being quicker or slower than the one which carries the spectator. The difficulty in determining to which of these causes the motion of the light is to be attributed, arises from the want of some intervening object whose state is known, and by which the apparent motion may be compared. Now this is precisely the situation in which we stand with regard to the heavenly bodies. For the motion of the earth ou its axis, if it really has such a motion, must be incomparably smoother than any vessel or machine made by human art; and as there is no fixed intermediate object between it and the heavenly bodies, no direct proof of this motion can be obtained.

As far, then, as appearances enable us to judge, either the earth may be at rest, and the heavens carried round it every twenty-four hours, or the heavens may be at rest, and the earth revolve round its axis, in the same time. For the rising and setting of the sun and stars, with all the other celestial phenomena, will be presented in the same order whether the heavens revolve round the earth, or the earth round its axis.

However, on comparing these appearances with others which are more within our reach, and with the established laws of motion, we