THE CLOUD-CHARIOTS.

§ 1. Between the flocks of small countless clouds which occupy the highest heavens, and the gray undivided film of the true rain-cloud, form the fixed masses or torn fleeces, sometimes collected and calm, sometimes fiercely drifting, which are, nevertheless, known under one general name of cumulus, or heaped cloud.

The true cumulus, the most majestic of all clouds, and almost the only one which attracts the notice of ordinary observers, is for the most part windless; the movement of its masses being solemn, continuous, inexplicable, a steady advance or retiring, as if they were animated by an inner will, or compelled by an unseen power. They appear to be peculiarly connected with heat, forming perfectly only in the afternoon, and melting away in the evening. Their noblest conditions are strongly electric, and connect themselves with storm-cloud and true thunder-cloud. When there is thunder in the air, they will form in cold weather, or early in the day.

§ 2. I have never succeeded in drawing a cumulus. Its divisions of surface are grotesque and endless, as those of a mountain;—perfectly defined, brilliant beyond all power of color, and transitory as a dream. Even Turner never attempted to paint them, any more than he did the snows of the high Alps.

Nor can I explain them any more than I can draw them. The ordinary account given of their structure is, I believe, that the moisture raised from the earth by the sun’s heat becomes visible by condensation at a certain height in the colder air, that the level of the condensing point is that of the cloud’s base, and that above it, the heaps are pushed up higher and higher as more vapor accumulates, till, towards evening, the supply beneath ceases; and at sunset, the fall of dew enables the surrounding atmosphere to absorb and melt them away. Very plausible. But it seems to me herein unexplained how the vapor is held together in those heaps. If the clear air about and above it has no aqueous vapor in it, or at least a much less quantity, why does not the clear air keep pulling the cloud to pieces, eating it away, as steam is consumed in open air? Or, if any cause prevents such rapid devouring of it, why does not the aqueous vapor diffuse itself softly in the air like smoke, so that one would not know where the cloud ended? What should make it bind itself in those solid mounds, and stay so:—positive, fantastic, defiant, determined?

§ 3. If ever I am able to understand the process of the cumulus formation,[1] it will become to me one of the most interesting of all subjects of study to trace the connection of the threatening and terrible outlines of thunder-cloud with the increased action of the electric power. I am for the present utterly unable to speak respecting this matter, and must pass it by, in all humility, to say what little I have ascertained respecting the more broken and rapidly moving forms of the central clouds, which connect themselves with mountains, and may, therefore, among mountains, be seen close and truly.

§ 4. Yet even of these, I can only reason with great doubt and continual pause. This last volume ought certainly to be better than the first of the series, for two reasons. I have learned, during the sixteen years, to say little where I said much, and to see difficulties where I saw none. And I am in a great state of marvel in looking back to my first account of clouds, not only at myself, but even at my dear master, M. de Saussure. To think that both of us should have looked at drifting mountain clouds, for years together, and been content with the theory which you will find set forth in § 4, of the chapter on the central cloud region (Vol. I.), respecting the action of the snowy summits and watery vapor passing them. It is quite true that this action takes place, and that the said fourth paragraph is right, as far as it reaches. But both Saussure and I ought to have known—we both did know, but did not think of it—that the covering or cap-cloud forms on hot summits as well as cold ones;—that the red and bare rocks of Mont Pilate, hotter, certainly, after a day’s sunshine than the cold storm-wind which sweeps to them from the Alps, nevertheless have been renowned for their helmet of cloud, ever since the Romans watched the cloven summit, gray against the south, from the ramparts of Vindonissa, giving it the name from which the good Catholics of Lucerne have warped out their favorite piece of terrific sacred biography.[2] And both my master and I should also have reflected, that if our theory about its formation had been generally true, the helmet cloud ought to form on every cold summit, at the approach of rain, in approximating proportions to the bulk of the glaciers; which is so far from being the case that not only (A) the cap-cloud may often be seen on lower summits of grass or rock, while the higher ones are splendidly clear (which may be accounted for by supposing the wind containing the moisture not to have risen so high), but (B) the cap-cloud always shows a preference for hills of a conical form, such as the Mole or Niesen, which can have very little power in chilling the air, even supposing they were cold themselves, while it will entirely refuse to form round huge masses of mountain, which, supposing them of chilly temperament, must have discomforted the atmosphere in their neighborhood for leagues. And finally (C) reversing the principle under letter A, the cap-cloud constantly forms on the summit of Mont Blanc, while it will obstinately refuse to appear on the Dome du Goûte or Aiguille Sans-nom, where the snow-fields are of greater extent, and the air must be moister, because lower.

J. Ruskin.J. C. Armytage.
69. Aiguilles and their Friends.
Fig. 86.

§ 5. The fact is, that the explanation given in that fourth paragraph can, in reality, account only for what may properly be termed “lee-side cloud,” slightly noticed in the continuation of the same chapter, but deserving most attentive illustration, as one of the most beautiful phenomena of the Alps. 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. In Fig. 86 the dark mass represents the mountain peak, the arrow the main direction of the wind, the curved lines show the directions of such current and its concentration, and the dotted lines enclose the space in which cloud forms densely, floating away beyond and above in irregular tongues and flakes. The second figure from the top in Plate 69 represents the actual aspect of it when in full development, with a strong south wind, in a clear day, on the Aiguille Dru, the sky being perfectly blue and lovely around.