Aqueous vapor or mist, suspended in the atmosphere, becomes visible exactly as dust does in the air of a room. In the shadows you not only cannot see the dust itself, because unillumined, but you can see other objects through the dust without obscurity, the air being thus actually rendered more transparent by a deprivation of light. Where a sunbeam enters, every particle of dust becomes visible, and a palpable interruption to the sight, so that a transverse sunbeam is a real obstacle to the vision, you cannot see things clearly through it.
In the same way, wherever vapor is illuminated by transverse rays, there it becomes visible as a whiteness more or less affecting the purity of the blue, and destroying it exactly in proportion to the degree of illumination. But where vapor is in shade, it has very little effect on the sky, perhaps making it a little deeper and grayer than it otherwise would be, but not itself, unless very dense, distinguishable or felt as mist.
The appearance of mist or whiteness in the blue of the sky, is thus a circumstance which more or less accompanies sunshine, [§ 14. They are only illuminated mist, and cannot appear when the sky is free from vapor, nor when it is without clouds.]and which, supposing the quantity of vapor constant, is greatest in the brightest sunlight. When there are no clouds in the sky, the whiteness, as it affects the whole sky equally, is not particularly noticeable. But when there are clouds between us and the sun, the sun being low, those clouds cast shadows along and through the mass of suspended vapor. Within the space of these shadows, the vapor, as above stated, becomes transparent and invisible, and the sky appears of a pure blue. But where the sunbeams strike, the vapor becomes visible in the form of the beams, occasioning those radiating shafts of light which are one of the most valuable and constant accompaniments of a low sun. The denser the mist, the more distinct and sharp-edged will these rays be; when the air is very clear, they are mere vague, flushing, gradated passages of light; when it is very thick, they are keen-edged and decisive in a high degree.
We see then, first, that a quantity of mist dispersed through the whole space of the sky, is necessary to this phenomenon; and secondly, that what we usually think of as beams of greater brightness than the rest of the sky, are in reality only a part of that sky in its natural state of illumination, cut off and rendered brilliant by the shadows from the clouds,—that these shadows are in reality the source of the appearance of beams,—that, therefore, no part of the sky can present such an appearance, except when there are broken clouds between it and the sun; and lastly, that the shadows cast from such clouds are not necessarily gray or dark, but very nearly of the natural pure blue of a sky destitute of vapor.
Now, as it has been proved that the appearance of beams can only take place in a part of the sky which has clouds between it [§ 15. Erroneous tendency in the representation of such phenomena by the old masters.]and the sun, it is evident that no appearance of beams can ever begin from the orb itself, except when there is a cloud or solid body of some kind between us and it; but that such appearances will almost invariably begin on the dark side of some of the clouds around it, the orb itself remaining the centre of a broad blaze of united light. Wordsworth has given us in two lines, the only circumstances under which rays can ever appear to have origin in the orb itself:—
"But rays of light,
Now suddenly diverging from the orb,
Retired behind the mountain tops, or veiled
By the dense air, shot upwards."
Excursion, Book IX.
And Turner has given us the effect magnificently in the Dartmouth of the River Scenery. It is frequent among the old masters, and constant in Claude; though the latter, from drawing his beams too fine, represents the effect upon the dazzled eye rather than the light which actually exists, and approximates very closely to the ideal which we see in the sign of the Rising Sun; nay, I am nearly sure that I remember cases in which he has given us the diverging beam, without any cloud or hill interfering [§ 16. The ray which appears in the dazzled eye should not be represented.]with the orb. It may, perhaps, be somewhat difficult to say how far it is allowable to represent that kind of ray which is seen by the dazzled eye. It is very certain that we never look towards a bright sun without seeing glancing rays issue from it; but it is equally certain that those rays are no more real existences than the red and blue circles which we see after having been so dazzled, and that if we are to represent the rays we ought also to cover our sky with pink and blue circles. I should on the whole consider it utterly false in principle to represent the visionary beam, and that we ought only to show [§ 17. The practice of Turner. His keen perception of the more delicate phenomena of rays.]that which has actual existence. Such we find to be the constant practice of Turner. Even where, owing to interposed clouds, he has beams appearing to issue from the orb itself, they are broad bursts of light, not spiky rays; and his more usual practice is to keep all near the sun in one simple blaze of intense light, and from the first clouds to throw beams to the zenith, though he often does not permit any appearance of rays until close to the zenith itself. Open at the 80th page of the Illustrated edition of Rogers's poems. You have there a sky blazing with sunbeams; but they all begin a long way from the sun, and they are accounted for by a mass of dense clouds surrounding the orb itself. Turn to the 7th page. Behind the old oak, where the sun is supposed to be, you have only a blaze of undistinguished light; but up on the left, over the edge of the cloud, on its dark side, the sunbeam. Turn to page 192,—blazing rays again, but all beginning where the clouds do, not one can you trace to the sun; and observe how carefully the long shadow on [§ 18. The total absence of any evidence of such perception in the works of the old masters.]the mountain is accounted for by the dim dark promontory projecting out near the sun. I need not multiply examples; you will find various modifications and uses of these effects throughout his works. But you will not find a single trace of them in the old masters. They give you the rays issuing from behind black clouds, and because they are a coarse and common effect which could not possibly escape their observation, and because they are easily imitated. They give you the spiky shafts issuing from the orb itself, because these are partially symbolical of light, and assist a tardy imagination, as two or three rays scratched round the sun with a pen would, though they would be rays of darkness instead of light.[[30]] But of the most beautiful phenomenon of all, the appearance of the delicate ray far in the sky, threading its way among the thin, transparent clouds, while all around the sun is unshadowed fire, there is no record nor example whatsoever in their works. It was too delicate and spiritual for them; probably their blunt and feelingless eyes never perceived it in nature, and their untaught imaginations were not likely to originate it in the study.
Little is to be said of the skies of our other landscape artists. In paintings, they are commonly toneless, crude, and wanting in depth and transparency; but in drawings, some very [§ 19. Truth of the skies of modern drawings.]perfect and delicate examples have been produced by various members of the old water color Society, and one or two others; but with respect to the qualities of which we are at present speaking, it is not right to compare drawings with paintings, as the wash or spunging, or other artifices peculiar to water color, are capable of producing an appearance of quality which it needs much higher art to produce in oils.
Taken generally, the open skies of the moderns are inferior in quality to picked and untouched skies of the greatest of the ancients, but far superior to the average class of pictures which [§ 20. Recapitulation. The best skies of the ancients are, in quality, inimitable, but in rendering of various truth, childish.]we have every day fathered upon their reputation. Nine or ten skies of Claude might be named which are not to be contended with, in their way, and as many of Cuyp. Teniers has given some very wonderful passages, and the clearness of the early Italian and Dutch schools is beyond all imitation. But the common blue daubing which we hear every day in our best galleries attributed to Claude and Cuyp, and the genuine skies of Salvator, and of both the Poussins, are not to be compared for an instant with the best works of modern times, even in quality and transparency; while in all matters requiring delicate observation or accurate science,—in all which was not attainable by technicalities of art, and which depended upon the artist's knowledge and understanding of nature, all the works of the ancients are alike the productions of mere children, sometimes manifesting great sensibility, but proving at the same time, feebly developed intelligence and ill-regulated observation.