Amazulu

“ Soon, however, the heavy masses of clouds in the northeast, that drove wildly before every ice-winged impulse of the storm-king, overwhelmed and shrouded the silver disc from sight, and gave forth the tempest they had so long threatened. Still, now and then, as the wrathful clouds would separate for a moment, a faint lustre would dart forth, sprinkling, as with the purple glories of the orient morn, the torn and ragged opening, and illuminating the landscape with a quaint beauty—half light and half shadow—then all would become dark again. ”

“ You see that no mistake is possible here about what is good weather and what bad, or which is cloud and which is sky; but I show you this sketch especially to give you the scale of heights for such clouds in the atmosphere. These thunder cumuli entirely hide the higher Alps. It does not, however, follow that they have buried them, for most of their own aspect of height is owing to the approach of their nearer masses; but at all events, you have cumulus there rising from its base, at about three thousand feet above the plain, to a good ten thousand in the air. ”

“ We next come to a variety which is anything but a harbinger of good, namely, the long stripes or bands of cirrus which stretch outwards from the margin of the cloud canopy of a cyclonic storm. In some ways these appendages to the great nimbus resemble the strips of cirriform cloud which fringe the summit of a thunder-cloud. They look as if they must have been formed by the blowing away, by a rapid wind, of the top of an uprising column of vapour-charged air. ”

“ A cloud upon the dome and these ever varying rockings and bendings of the falls are sure storm signs, but yesterday morning’s sky was clear, and the sun poured the usual quantity of the balmiest spring sunshine into the blue ether of our valley gulf, but ere long ragged lumps of cloud began to appear all along the valley-rim, coming gradually into closer ranks, and rising higher like rock additions to the walls. ”

“ It is not clear whether the light of the cloud means the lightning again or the varied hues which make an Oriental sunset glorious in purple and gold. But the balancings of the clouds must be that singular power which the atmosphere has of sustaining vast quantities of watery vapour—either miles above the earth's surface where the filmy cirrhus floats, dazzling white against the blue sky, or lower down where the rain-cloud trails along the hill-tops. ”

“ Its very immensity gives a mystery to it: sometimes the air is clear as crystal, and the white clouds on the horizon seem to be touching some far-distant fold of the landscape; at others the plain dances in the heat, and great mirage lakes can be seen covering the middle distances; again, thunderstorms pass along the sky, whose piled masses of cumuli clouds send down ribbons of fire, often causing fires that sweep for miles over the open grassland. ”

“ The stratum of cloud, at first high in the atmosphere, gradually lowers itself, and the traveller is enveloped in a frozen mist, followed most commonly during the night by a fall of snow. The quantity of snow which falls is very small, seldom, so far as I have seen, more than an inch or two in depth, and it speedily disappears as soon as the clouds have been dissipated and the sky resumes its usual serenity. ”

“ When a moist wind blows in clear weather over a cold summit, it has not time to get chilled as it approaches the rock, and therefore the air remains clear, and the sky bright on the windward side; but under the lee of the peak, there is partly a back eddy, and partly still air; and in that lull and eddy the wind gets time to be chilled by the rock, and the cloud appears, as a boiling mass of white vapor, rising continually with the return current to the upper edge of the mountain, where it is caught by the straight wind and partly torn, partly melted away in broken fragments. ”

“ A few fleecy clouds in the west partially obscured the sun until it neared the horizon, then a shaft of sunlight broke through once more, telegraphing its approach long before it reached us, the rays being visibly hurled through space like a javelin, or a lightning bolt, striking peak after peak so that one almost imagined they would hear the thunder roll. ”

“ On what anvils and wheels is the vapor pointed, twisted, hammered, whirled, as the potter's clay? By what hands is the incense of the sea built up into domes of marble?"
[9] The opposed conditions of the higher and lower orders of cloud, with the balanced intermediate one, are beautifully seen on mountain summits of rock or earth. On snowy ones [37] they are far more complex: but on rock summits there are three distinct forms of attached cloud in serene weather ”

“ After the sun has passed the meridian, clouds have been collecting, generally from the north-east, and as evening advances, the vivid lightning and the heavy peals of thunder commence, and last for several hours, and then appear to evaporate, and a lovely starlight night succeeds; not a drop of rain has fallen during the storm, and a clear blue sky is seen over the whole of the horizon. ”

“ The Alps, under the rose [A] of sunset, are exactly of the same [42] color whether you see them from Berne or Schaffhausen. But the gilding to our eyes of a burnished cloud depends, I believe, at least for a measure of its luster, upon the angle at which the rays incident upon it are reflected to the eye, just as much as the glittering of the sea beneath it—or the sparkling of the windows of the houses on the shore. ”

“ For the sky is covered with gray cloud;—not rain-cloud, but a dry black veil, which no ray of sunshine can pierce; partly diffused in mist, feeble mist, enough to make distant objects unintelligible, yet without any substance, or wreathing, or color of its own. And everywhere the leaves of the trees are shaking fitfully, as they do before a thunder-storm ”

“ How is a cloud outlined? Granted whatever you choose to ask, concerning its material, or its aspect, its loftiness and luminousness,—how of its limitation? What hews it into a heap, or spins it into a web? Cold is usually shapeless, I suppose, extending over large spaces equally, or with gradual diminution. You cannot have in the open air, angles, and wedges, and coils, and cliffs, of cold. Yet the vapor stops suddenly, sharp and steep as a rock, or thrusts itself across the gates of heaven in likeness of a brazen bar ”

“ I have myself, in many of the passages of 'Modern Painters' before referred to, conceived of cloud too narrowly as always produced by cold, whereas the temperature of a cloud must continually, like that of our visible breath in frosty weather, or of the visible current of steam, or the smoking of a warm lake surface under sudden frost, be above that of the surrounding atmosphere; and yet I never remember entering a cloud without being chilled by it, and the darkness of the plague-wind, unless in electric states of the air, is always accompanied by deadly chill. ”

“ Once, one hot afternoon, the air took on an oppressive density, the wind died away almost to a calm, blowing fitfully from the south, while in the far west a vast dome of inky clouds, silent and portentous, uplifted, filling the horizon, swelling like a great bubble, yet seeming to have the weight of a mountain range in its mass. ”

“ The rapid changes of temperature in summer and the sudden rising of vast masses of heated air produce cloud-structures of the most imposing description, especially huge, irregular cumulus clouds that float in equilibrium above us like colossal icebergs, airy mountain-ranges or tottering battlemented towers and "looming bastions fringed with fire." ”

“ The seemingly harmless clouds that had overhung the mountains since morning had now accumulated in threatening masses, and rolled in huge gray vapors over all the heavens. A wet, penetrating mist overspread the earth, and a chill wind that smelt already of the rain blew drearily, now and then shaking down showers of condensed moisture from the faded trees. ”

“ In each of these lofty mountain regions the precipitation is known to be heaviest at moderate altitudes, while higher up it decreases markedly. The reason is that the storm clouds—the clouds that carry most of the rain and snow—hang in a zone of only moderate elevation, while higher up the atmosphere contains but little moisture and seldom forms clouds of any great density. ”

“ The southeast wind causes a mass of air, equal to the diameter of the mountain, suddenly to ascend at least three thousand feet; the dilatation produced by altitude, with its attendant cold, causes the immediate formation of a cloud on the summit; the water in the atmosphere becomes visible; successive masses of gliding-up and passing-over air cause the continual formation of clouds, but the top of the vapory mass, or "table-cloth", is level, and seemingly motionless ”

“ Thus the snow flows fast or slow in grand beauty-making glaciers and avalanches; the air in majestic floods carrying minerals, plant leaves, seeds, spores, with streams of music and fragrance; water streams carrying rocks both in solution and in the form of mud particles, sand, pebbles, and boulders. Rocks flow from volcanoes like water from springs, and animals flock together and flow in currents modified by stepping, leaping, gliding, flying, swimming, etc. While the stars go streaming through space pulsed on and on forever like blood globules in Nature’s warm heart. ”

“ But there is also the chance of that most glorious of transfigurations of earth and sky, when towards evening some breath of air sweeps away the local storm, and through the melting 24 cloud-wreaths we see the wide landscape glittering with fresh rain, and the new snows shining opposite the setting sun—a scene the full splendour of which can scarcely be recalled even in the memory of those who have often witnessed it. ”

“ Ceaseless precipitation goes on under this cloudring. Evaporation under it is suspended almost entirely. We know that the trade-winds encircle the earth; that they blow perpetually; that they come from the north and the south, and meet each other near the equator; therefore we infer that this line of meeting extends around the world. By the rainy seasons of the torrid zone we can trace the declination of this cloud-ring stretched like a girdle round about the earth: it travels up and down the ocean as from north to south and back. ”

“ I have defined the floating or sky cloud, and defined the falling, or earth cloud. But there's a sort of thing between the two, which needs a third definition: namely, Mist. In the 22d page of his 'Glaciers of [10] the Alps,' Professor Tyndall says that "the marvelous blueness of the sky in the earlier part of the day indicated that the air was charged, almost to saturation, with transparent aqueous vapor." Well, in certain weather that is true. You all know the peculiar clearness which precedes rain,—when the distant hills are looking nigh. ”

“ But, as I had left my coat in camp for the sake of having my limbs free in climbing, I soon was cold. The wind increased in violence, raising the snow in magnificent drifts that were drawn out in the form of wavering banners blowing in the sun. Toward the end of my stay a succession of small clouds struck against the summit rocks like drifting icebergs, darkening the air as they passed, and producing a chill as definite and sudden as if ice-water had been dashed in my face. This is the kind of cloud in which snow-flowers grow, and I turned and fled. ”

“ Quarter to eight, morning.—Thunder returned, all the air collapsed into one black fog, the hills invisible, and scarcely visible the opposite shore; heavy rain in short fits, and frequent, though less formidable, flashes, and shorter thunder. While I have written this sentence the cloud has again dissolved itself, like a nasty solution in a bottle, with miraculous and unnatural rapidity, and the hills are in sight again ”

“ The Storm King of the North is abroad to day, working with a fine, hearty enthusiasm, rolling a multitude of white combing waves through the rocky, jagged straits between this marvelous chain of islands, circling them about with beaten foam, and heaping a lavish abundance of snow on their lofty, cloud-wrapped mountains. The deep bass of the gale, sounding on through the rugged, ice-sculptured peaks and gorges, is delightful music to our ears, now that we are safely sheltered in a land-locked harbor. ”

“ The clouds are chiefly cumulus, cumulo-stratus, and nimbus; the sky is often overcast with large white masses floating, apparently without motion, upon the milky haze, and in the serenest weather a few threads are seen pencilled upon the expanse above. ”

“ We may also add the shading of the underlying ground by the cloud itself, and the absorption of heat in the partial evaporation of some of the rain during the lower part of its fall. In a desert district the arising currents are so dry that even a very great ascent does not often result in visible cloud; and when it does, the cloud is produced at so great a height that the air is too rarefied to produce anything much denser than thin alto-stratus, from which no falling droplets could reach the earth. ”

“ The big drops sift through the pine-needles, plash and patter on the granite pavements, and pour down the sides of ridges and domes in a network of gray, bubbling rills. In a few minutes the cloud withers to a mesh of dim filaments and disappears, leaving the sky perfectly clear and bright, every dust-particle wiped and washed out of it. Everything is refreshed and invigorated, a steam of fragrance rises, and the storm is finished—one cloud, one lightning-stroke, and one dash of rain. This is the Sierra mid-summer thunder-storm reduced to its lowest terms. ”