pallio-cirrus, it disappears entirely if fine weather is maintained. Let us now see what are the inherent characters of the two pallio.

V.-PALLIO-CIRRUS, (POËY.)

Sheet-cloud, (illustration No. IX.)-The pallio-cirrus is formed by the accumulation of a cirro-cumulus, which is visibly sinking, or appears already formed toward a point of the horizon in the stratum, corresponding to this latter type. In the first case it is a little lower, more dense, less compact, more rapid in its movement, grayish, and often shows some traces of polarization. In the second case it is a little higher, less dense, more compact, less rapid, pearly whitish, impenetrable to the solar rays, and without a trace of polarization. In the two cases it appears generally in the southwesterly horizon, showing the presence of the superior equatorial current, and determining the fall of rain while it remains above and opposite the pallio-cumulus. When a breach is made in this inferior stratum it is speedily produced in that of the pallio-cirrus; sometimes it has already been formed in the latter. After the rupture of this stratum, the pallio-cirrus is transformed into cirro-cumulus, studded with cirrostratus. On the approach of pallio cirrus we observe the following meteorological manifestations: the barometer falls, the thermometer rises, the relative humidity increases, the tension of vapor diminishes, and a little after the wind at the earth is felt from that direction.

VI.—CUMULUS, (vel CUMULO-STRATUS,) (HOWARD.)

Mount-cloud, (illustrations Nos. X and XI.)-Howard's cumulus,(or cumulo-stratus,) summer and aqueous vesicle clouds, (the "cotton-balls" of sailors,) always appear in the form of a hemisphere or arcs of a circle, and repose upon a horizontal base. When these hemispheres are piled upon one an other, there are formed great clouds accumulated at the horizon, similar to mountains in the distance covered with snow. Their contours take many forms, human, animal, and of every kind, more or less bizarre and fantastic, which inspired the poet Ossian with his finest images, and have given rise in mountainous countries to many popular traditions.

When the cumulus moves along the horizon, it is, excepting fractocumulus, the most rapid of all clouds. But when it is piled up along the horizon, in summer toward the south, in winter toward the north, it is excessively slow, and remains a whole day scarcely moving. It then extends perpendicularly or obliquely toward the zenith. Its roundish summit is of a glittering whiteness, and when elevated high enough, it is dyed rose color morning and evening like the cirrus. The center of the cloud is grayish, the base slate color or black. The base of the cumulus always rests upon the horizon, and is little elevated dur ing a storm. It follows the direction of surface winds. Upon the plateau of the valley of Mexico, the cumulus completely disappears during the winter half of the year, and appears anew during the other six months. In summer it appears about eight or nine c'clock in the morn

ing. It attains its highest elevation from two to three o'clock in the afternoon, during the greatest heat, after which it fades away gradually, and a little after sun-down disappears entirely behind the hills. Thus cumulus in Mexico is only visible in summer and during the day. Howard says:

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 afterward continue long nearly of the same bulk or rapidly grow to the size of mountains.

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 lie always 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 sunrise, arrive at their maximum in the hottest part of the afternoon, then go on diminishing, and totally disperse about sunset.

But in changeable 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.

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

Independently of the beauty and magnificence it adds to the face of nature, the cumnlus serves to screen the earth from the direct rays of the sun; by its multiplied reflections to diffuse, and, as it were, economize 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 enough attended to.

VII.-PALLIO-CUMULUS, (POËY.)

Fain-cloud, (illustration No. XII.)—The pallio-cumulus is produced by the accumulation of fracto-cumulus, which is gradually extended under the for n of a uniform and compact stratum. This stratum is constantly sus tained by the entrance of new fracto-cumuli, which increase its thickness un til rain begins; then the fracto-cumulus ceases to penetrate it, and passes along the stratum of pallio-cumulus, but before the end of the rain it is disengaged anew from the stratum, which grows thin, is broken up and disappears. The pallio-cumulus is lower, more dense, less compact, more rapid than the pallio-cirrus, and is slate-colored or grayish. The thicker and more compact this stratum is, the longer will the rain continue; but as soon as a breach is made, it disengages fragments of cumulus, (fracto-cumulus,) which rapidly disappear, while the remainder are piled up at the horizon in the form of cumulus. The pallio-cumulus appears almost always from the northeast, showing the inferior polar current, which soon reaches the surface of the earth. The meteorological manifestations determined by them are inverse to those of pallio-cirrus; the