Chapter III: 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.

69. Aiguilles and their Friends.]

§ 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.

So far all is satisfactory. But the true helmet cloud will not allow itself to be thus explained away. The uppermost figure in Plate 69 represents the loveliest form of it, seen in that perfect arch, so far as I know, only over the highest piece of earth in Europe.

§ 6. Respecting which there are two mysteries:--First, why it should form only at a certain distance above the snow, showing blue sky between it and the summit. Secondly, why, so forming, it should always show as an arch, not as a concave cup. This last question puzzles me especially. For, if it be a true arch, and not a cup, it ought to show itself in certain positions of the spectator, or directions of the wind, like the ring of Saturn, as a mere line, or as a spot of cloud pausing over the hill-top. But I never saw it so. While, as above noticed, the lowest form of the helmet cloud is not white as of silver, but like Dolon's helmet of wolf-skin,--it is a gray, flaky veil, lapping itself over the shoulders of a more or less conical peak; and of this, also, I have no word to utter but the old one, "Electricity," and I might as well say nothing.

§ 7. Neither the helmet cloud, nor the lee-side cloud, however, though most interesting and beautiful, are of much importance in picturesque effect. They are too isolated and strange. But the great mountain cloud, which seems to be a blending of the two with independent forms of vapor (that is to say, a greater development, in consequence of the mountain's action, of clouds which would in some way or other have formed anywhere), requires prolonged attention, as the principal element of the sky in noblest landscape.

§ 8. For which purpose, first, it may be well to clear a few clouds out of the way. I believe the true cumulus is never seen in a great mountain region, at least never associated with hills. It is always broken up and modified by them. Boiling and rounded masses of vapor occur continually, as behind the Aiguille Dru (lowest figure in Plate 69); but the quiet, thoroughly defined, infinitely divided and modelled pyramid never develops itself. It would be very grand if one ever saw a great mountain peak breaking through the domed shoulders of a true cumulus; but this I have never seen.

§ 9. Again, the true high cirri never cross a mountain in Europe. How often have I hoped to see an Alp rising through and above their level-laid and rippled fields! but those white harvest-fields are heaven's own. And, finally, even the low, level, cirrus (used so largely in Martin's pictures) rarely crosses a mountain. If it does, it usually becomes slightly waved or broken, so as to destroy its character. Sometimes, however, at great distances, a very level bar of cloud will strike across a peak; but nearer, too much of the under surface of the field is seen, so that a well-defined bar across a peak, seen at a high angle, is of the greatest rarity.

70. The Graiæ.]

§ 10. The ordinary mountain cloud, therefore, if well defined, divides itself into two kinds: a broken condition of cumulus, grand in proportion as it is solid and quiet,--and a strange modification of drift-cloud, midway, as I said, between the helmet and the lee-side forms. The broken, quiet cumulus impressed Turner exceedingly when he first saw it on hills. He uses it, slightly exaggerating its definiteness, in all his early studies among the mountains of the Chartreuse, and very beautifully in the vignette of St. Maurice in Rogers's Italy. There is nothing, however, to be specially observed of it, as it only differs from the cumulus of the plains, by being smaller and more broken.

§ 11. Not so the mountain drift-cloud, which is as peculiar as it is majestic. The Plates 70 and 71 show, as well as I can express, two successive phases of it on a mountain crest; (in this instance the great limestone ridge above St. Michel, in Savoy.) But what colossal proportions this noble cloud assumes may be best gathered from the rude sketch, Fig. 87, in which I have simply put firm black ink over the actual pencil lines made at the moment, giving the form of a single wreath of the drift-cloud, stretching about five miles in a direct line from the summit of one of the Alps of the Val d'Aosta, as seen from the plain of Turin. It has a grand volcanic look, but I believe its aspect of rising from the peak to be almost, if not altogether, deceptive; and that the apparently gigantic column is a nearly horizontal stream of lee-side cloud, tapered into the distance by perspective, and thus rising at its apparently lowest but in reality most distant point, from the mountain summit whose shade calls it into being out of the clear winds.

Whether this be so or not, the apparent origin of the cloud on the peak, and radiation from it, distinguish it from the drift-cloud of level country, which arranges itself at the horizon in broken masses, such as Fig. 89, showing no point of origin; and I do not know how far they are vertical cliffs or horizontally extended fields. They are apt to be very precipitous in aspect, breaking into fragments with an apparently concentric motion, as in the figure; but of this motion also--whether vertical or horizontal--I can say nothing positive.

§ 12. The absolute scale of such clouds may be seen, or at least demonstrated, more clearly in Fig. 88, which is a rough note of an effect of sky behind the tower of Berne Cathedral. It was made from the mound beside the railroad bridge. The Cathedral tower is half-a-mile distant. The great Eiger of Grindelwald is seen just on the right of it. This mountain is distant from the tower thirty-four miles as the crow flies, and ten thousand feet above it in height. The drift-cloud behind it, therefore, being in full light, and showing no overhanging surfaces, must rise at least twenty thousand feet into the air.

§ 13. The extreme whiteness of the volume of vapor in this case (not, I fear, very intelligible in the woodcut[3]) may be partly owing to recent rain, which, by its evaporation, gives a peculiar density and brightness to some forms of clearing cloud. In order to understand this, we must consider another set of facts. When weather is thoroughly wet among hills, we ought no more to accuse the mountains of forming the clouds, than we do the plains in similar circumstances. The unbroken mist buries the mountains to their bases; but that is not their fault. It may be just as wet and just as cloudy elsewhere. (This is not true of Scottish mountain, by the way.) But when the wet weather is breaking, and the clouds pass, perhaps, in great measure, away from the plains leaving large spaces of blue sky, the mountains begin to shape clouds for themselves. The fallen moisture evaporates from the plain invisibly; but not so from the hill-side. There, what quantity of rain has not gone down in the torrents, ascends again to heaven instantly in white clouds. The storm passes as if it had tormented the crags, and the strong mountains smoke like tired horses.

§ 14. Here is another question for us of some interest. Why does the much greater quantity of moisture lying on the horizontal fields send up no visible vapor, and the less quantity left on the rocks glorify itself into a magnificent wreath of soaring snow?

First, for the very reason, that it is less in quantity, and more distributed; as a wet cloth smokes when you put it near the fire, but a basin of water not.

The previous heat of the crags, noticed in the first volume, p. 249, is only a part of the cause. It operates only locally, and on remains of sudden showers. But after any number of days and nights of rain, and in all places exposed to returning sunshine and breezes, the _distribution_ of the moisture tells. So soon as the rain has ceased, all water that can run off is of course gone from the steep hill-sides; there remains only the thin adherent film of moisture to be dried; but that film is spread over a complex texture--all manner of crannies, and bosses, and projections, and filaments of moss and lichen, exposing a vast extent of drying surface to the air. And the evaporation is rapid in proportion.

§ 15. Its rapidity, however, observe, does not account for its visibility, and this is one of the questions I cannot clearly solve, unless I were sure of the nature of the vesicular vapor. When our breath becomes visible on a frosty day, it is easily enough understood that the moisture which was invisible, carried by the warm air from the lungs, becomes visible when condensed or precipitated by the surrounding chill; but one does not see why air passing over a moist surface quite as cold as itself should take up one particle of water more than it can conveniently--that is to say, invisibly--carry. Whenever you _see_ vapor, you may not inaccurately consider the air as having got more than it can properly hold, and dropping some. Now it is easily understood how it should take up much in the lungs, and let some of it fall when it is pinched by the frost outside; but why should it overload itself there on the hills, when it is at perfect liberty to fly away as soon as it likes, and come back for more? I do not see my way well in this. I do not see it clearly, even through the wet cloth. I shall leave all the embarrassment of the matter, however, to my reader, contenting myself, as usual, with the actual fact, that the hill-side air does behave in this covetous and unreasonable manner; and that, in consequence, when the weather is breaking (and sometimes, provokingly, when it is not), phantom clouds form and rise in sudden crowds of wild and spectral imagery along all the far succession of the hill-slopes and ravines.

§ 16. There is this distinction, however, between the clouds that form during the rain and after it. In the worst weather, the rain-cloud keeps rather high, and is unbroken; but when there is a disposition in the rain to relax, every now and then a sudden company of white clouds will form quite low down (in Chamouni or Grindelwald, and such high districts, even down to the bottom of the valley), which will remain, perhaps, for ten minutes, filling all the air, then disappear as suddenly as they came, leaving the gray upper cloud and steady rain to their work. These "clouds of relaxation," if we may so call them, are usually flaky and horizontal, sometimes tending to the silky cirrus, yet showing no fine forms of drift; but when the rain has passed, and the air is getting warm, forms the true clearing cloud, in wreaths that ascend continually with a slow circling motion, melting as they rise. The woodcut, Fig. 91, is a rude note of it floating more quietly from the hill of the Superga, the church (nearly as large as St. Paul's) appearing above, and thus showing the scale of the wreath.

§ 17. This cloud of evaporation, however, does not always rise. It sometimes rests in absolute stillness, low laid in the hollows of the hills, their peaks emergent from it. Fig. 92 shows this condition of it, seen from a distance, among the Cenis hills. I do not know what gives it this disposition to rest in the ravines, nor whether there is a greater chill in the hollows, or a real action of gravity on the particles of cloud. In general, the position seems to depend on the temperature. Thus, in Chamouni, the crests of La Côte and Taconay continually appear in stormy weather as in Plate 36, Vol. IV., in which I intended to represent rising drift-cloud, made dense between the crests by the chill from the glaciers. But in the condition shown in Fig. 92, on a comparatively open sweep of hill-side, the thermometer would certainly indicate a higher temperature in the sheltered valley than on the exposed peaks; yet the cloud still subsides into the valleys like folds of a garment; and, more than this, sometimes conditions of morning cloud, dependent, I believe, chiefly on dew evaporation, form first on the _tops_ of the soft hills of wooded Switzerland, and droop down in rent fringes, and separate tongues, clinging close to all the hill-sides, and giving them exactly the appearance of being covered with white fringed cloth, falling over them in torn or divided folds. It always looks like a true action of gravity. How far it is, in reality, the indication of the power of the rising sun causing evaporation, first on the hill-top, and then in separate streams, by its divided light on the ravines, I cannot tell. The subject is, as the reader perceives, always inextricably complicated by these three necessities--that to get a cloud in any given spot, you must have moisture to form the material of it, heat to develop it, and cold[4] to show it; and the adverse causes inducing the moisture, the evaporation, and the visibility are continually interchanged in presence and in power. And thus, also, the phenomena which properly belong to a certain elevation are confused, among hills at least, with those which in plains would have been lower or higher.

I have been led unavoidably in this chapter to speak of some conditions of the rain-cloud; nor can we finally understand the forms even of the cumulus, without considering those into which it descends or diffuses itself. Which, however, being, I think, a little more interesting than our work hitherto, we will leave this chapter to its dulness, and begin another.

FOOTNOTES:

[1] One of the great difficulties in doing this is to distinguish the
portions of cloud outline which really slope upwards from those which
only appear to do so, being in reality horizontal, and thrown into
apparent inclination by perspective.

[2] _Pileatus_, capped (strictly speaking, with the cap of
liberty;--stormy cloud enough sometimes on men's brows as well as on
mountains), corrupted into Pilatus, and Pilate.

[3] I could not properly illustrate the subject of clouds without
numbers of these rude drawings, which would probably offend the
general reader by their coarseness, while the cost of engraving them
in facsimile is considerable, and would much add to the price of the
book. If I find people at all interested in the subject, I may,
perhaps, some day systematize and publish my studies of cloud
separately. I am sorry not to have given in this volume a careful
study of a rich cirrus sky, but no wood-engraving that I can employ
on this scale will express the finer threads and waves.

[4] We might say light, as well as cold; for it wholly depends on the
degree of light in the sky how far delicate cloud is seen.

The second figure from the top in Plate 69 shows an effect of morning
light on the range of the Aiguille Bouchard (Chamouni). Every crag
casts its shadow up into apparently clear sky. The shadow is, in such
cases, a bluish gray, the color of clear sky; and the defining light
is caused by the sunbeams showing mist which otherwise would have
been unperceived. The shadows are not irregular enough in
outline--the sketch was made for their color and sharpness, not their
shape,--and I cannot now put them right, so I leave them as they were
drawn at the moment.