Of the Perspective of Colours
Inany place where the light diminishes in a gradual proportion till it terminates in total darkness, the colours also will lose themselves and be dissolved in proportion as they recede from the eye.
Theprincipal colours, or those nearest to the eye, should be pure and simple; and the degree of their diminution should be in proportion to their distance, viz. the nearer they are to the principal point, the more they will possess of the purity of those colours, and they will partake of the colour of the horizon in proportion as they approach to it.
Ofall the colours which are not blue, those that are nearest to black will, when distant, partake most of the azure; and, on the contrary, those will preserve their proper colour at the greatest distance, that are most dissimilar to black.
The green therefore of the fields will change sooner into blue than yellow, or white, which will preserve their natural colour at a greater distance than that, or even red.
Thecolour will not be subject to any alteration when the distance and the quality of air have a reciprocal proportion. What it loses by the distance it regains by the purity of the air, viz. if we suppose the first or lowest air to have four degrees of thickness, and the colour to be at one degree from the eye,and the second air above to have three degrees. The air having lost one degree of thickness, the colour will acquire one degree upon the distance. And when the air still higher shall have lost two degrees of thickness, the colour will acquire as many upon the distance; and in that case the colour will be the same at three degrees as at one. But to be brief, if the colour be raised so high as to enter that quality of air which has lost three degrees of thickness, and acquired three degrees of distance, then you may be certain that that colour which is high and remote, has lost no more than the colour which is below and nearer; because in rising it has acquired those three degrees which it was losing by the same distance from the eye; and this is what was meant to be proved.
No Apparent Change in Colours
Itmay happen that a colour does not alter, though placed at different distances, when the thickness of the air and the distance are in the same inverse proportion. It is proved thus: let A be theeye, and H any colour whatever, placed at one degree of distance from the eye, in a quality of air of four degrees of thickness; but because the second degree above, A M N L, contains a thinner air by one half, which air conveys this colour, it follows that this colour will appear as if removed double the distance it was at before, viz. at two degrees of distance, A F and F G, from the eye; and it will be placed in G. If that is raised to the second degree of air A M N L, and to the degree O M, P N, it will necessarily be placed at E, and will be removed from the eye the whole length of the line A E, which will be proved in this manner to be equal in thickness to the distance A G. If in the same quality of air the distance A G interposed between the eye and the colour occupies two degrees, and A E occupies two degrees and a half, it is sufficient to preserve the colour G, when raised to E, from any change, because the degree A C and the degree A F being the same in thickness, are equal and alike, and the degree C D, though equal in length to the degree F G, is not alike in point of thickness of air; because half of it is situated in a degree of air of double the thickness of the air above: this half degree of distance occupies as much of the colour as one whole degree of the air above would, which air above is twice as thin as the air below, with which it terminates; so that by calculating the thickness of the air, and the distances, you will find that the colours have changed places without undergoing any alteration in their beauty. And we shall prove it thus: reckoningfirst the thickness of air, the colour H is placed in four degrees of thickness, the colour G in two degrees, and E at one degree. Now let us see whether the distances are in an equal inverse proportion; the colour E is at two degrees and a half of distance, G at two degrees, and H at one degree. But as this distance has not an exact proportion with the thickness of air, it is necessary to make a third calculation in this manner: A C is perfectly like and equal to A F; the half degree, C B, is like but not equal to A F, because it is only half a degree in length, which is equal to a whole degree of the quality of the air above; so that by this calculation we shall solve the question. For A C is equal to two degrees of thickness of the air above, and the half degree C B is equal to a whole degree of the same air above; and one degree more is to be taken in, viz. B E, which makes the fourth. A H has four degrees of thickness of air, A G also four, viz. A F two in value, and F G also two, which taken together make four. A E has also four, because A C contains two, and C D one, which is the half of A C, and in the same quality of air; and there is a whole degree above in the thin air, which all together make four. So that if A E is not double the distance A G, nor four times the distance A H, it is made equivalent by the half degree C B of thick air, which is equal to a whole degree of thin air above. This proves the truth of the proposition, that the colour H G E does not undergo any alteration by these different distances.
Manypainters will represent the objects darker, in proportion as they are removed from the eye; but this cannot be true, unless the objects seen be white; as shall be examined in the next chapter.
Theair tinges objects with its own colour more or less in proportion to the quantity of intervening air between it and the eye, so that a dark object at the distance of two miles (or a density of air equal to such distance), will be more tinged with its colour than if only one mile distant.
It is said, that, in a landscape, trees of the same species appear darker in the distance than near; this cannot be true, if they be of equal size, and divided by equal spaces. But it will be so if the first trees are scattered, and the light of the fields is seen through and between them, while the others which are farther off, are thick together, as is often the case near some river or other piece of water: in this case no space of light fields can be perceived, but the trees appear thick together, accumulating the shadow on each other. It also happens, that as the shady parts of plants are much broader than the light ones, the colour of the plants becoming darker by the multiplied shadows, is preserved, andconveyed to the eye more strongly than that of the other parts; these masses, therefore, will carry the strongest parts of their colour to a greater distance.
Thedarker the mountain is in itself, the bluer it will appear at a great distance. The highest part will be the darkest, as being more woody; because woods cover a great many shrubs, and other plants, which never receive any light. The wild plants of those woods are also naturally of a darker hue than cultivated plants; for oak, beech, fir, cypress, and pine trees are much darker than olive and other domestic plants. Near the top of these mountains, where the air is thinner and purer, the darkness of the woods will make it appear of a deeper azure, than at the bottom, where the air is thicker. A plant will detach very little from the ground it stands upon, if that ground be of a colour something similar to its own; and,vice versâ, that part of any white object which is nearest to a dark one, will appear the whitest, and the less so as it is removed from it; and any dark object will appear darker, the nearer it is to a white one; and less so, if removed from it.
Thereare some situations which, though light, appear dark, and in which objects are deprived bothof form and colour. This is caused by the great light which pervades the intervening air; as is observable by looking in through a window at some distance from the eye, when nothing is seen but an uniform darkish shade; but if we enter the house, we shall find that room to be full of light, and soon distinguish every small object contained within that window. This difference of effect is produced by the great brightness of the air, which contracts considerably the pupil of the eye, and by so doing diminishes its power. But in dark places the pupil is enlarged, and acquires as much in strength, as it increases in size. This is proved in my second proposition of perspective[73].
Thetermination and shape of the parts in general are very little seen, either in great masses of light, or of shadows; but those which are situated between the extremes of light and shade are the most distinct.
Perspective, as far as it extends in regard to painting, is divided into three principal parts; the first consists in the diminution of size, according to distance; the second concerns the diminution of colours in such objects; and the third treats of the diminution of the perception altogether of those objects, and of the degree of precision they ought to exhibit at various distances.
The azure of the sky is produced by a mixture composed of light and darkness[74]; I say of light, because of the moist particles floating in the air, which reflect the light. By darkness, I mean the pure air, which has none of these extraneous particles to stop and reflect the rays. Of this we see an example in the air interposed between the eye and some dark mountains, rendered so by the shadows of an innumerable quantity of trees; or else shaded on one side by the natural privation of the rays of the sun; this air becomes azure, but not so on the side of the mountain which is light, particularly when it is covered with snow.
Among objects of equal darkness and equal distance, those will appear darker that terminate upon a lighter ground, andvice versâ[75].
That object which is painted with the most white and the most black, will shew greater relief than any other; for that reason I would recommend to painters to colour and dress their figures with the brightest and most lively colours; for if they are painted of a dull or obscure colour, they will detach but little, and not be much seen, when the picture is placed at some distance; because the colour of every object is obscured in the shades; and if it be represented as originally so all over, there will be but little difference between the lights and the shades, while lively colours will shew a striking difference.
Thereis another kind of perspective called aerial, because by the difference of the air it is easy to determine the distance of different objects, though seen on the same line; such, for instance, as buildings behind a wall, and appearing all of the same height above it. If in your picture you want to have one appear more distant than another, you must first suppose the air somewhat thick, because, as we have said before, in such a kind of air the objects seen at a great distance, as mountains are, appear blueish like the air, by means of the great quantity of air that interposes between the eye and such mountains. You will then paint the first building behind that wall of its proper colour; the next in point of distance, less distinct in the outline, and participating, in a greater degree, of the blueish colour of the air; another which you wish to send off as much farther, should be painted as much bluer; and if you wish one of them to appear five times farther removed beyond the wall, it must have five times more of the azure. By this rule these buildings which appeared all of the same size, and upon the same line, will be distinctly perceived to be of different dimensions, and at different distances.
Ofobjects receding from the eye the smallest will be the first lost to the sight; from which it follows, that the largest will be the last to disappear. The painter, therefore, ought not to finish the parts of those objects which are very far off, but follow the rule given in the sixth book[76].
How many, in the representation of towns, and other objects remote from the eye, express every part of the buildings in the same manner as if they were very near. It is not so in nature, because there is no sight so powerful as to perceive distinctly at any great distance the precise form of parts or extremities of objects. The painter therefore who pronounces the outlines, and the minute distinction of parts, as several have done, will not give the representation of distant objects, but by this error will make them appear exceedingly near. Again, the angles of buildings in distant towns are not to be expressed (for they cannot be seen), considering that angles are formed by the concurrence of two lines into one point, and that a point has no parts; it is therefore invisible.
Objectsappear smaller than they really are when they are distant from the eye, and because there is a great deal of air interposed, which weakens the appearance of forms, and, by a natural consequence, prevents our seeing distinctly the minute parts of such objects. It behoves the painter therefore to touch those parts slightly, in an unfinished manner; otherwise it would be against the effect of Nature, whom he has chosen for his guide. For, as we said before, objects appear small on account of their great distance from the eye; that distance includes a great quantity of air, which, forming a dense body, obstructs the light, and prevents our seeing the minute parts of the objects.
Asthe air is thicker nearer the earth, and becomes thinner as it rises, look, when the sun is in the east, towards the west, between the north and south, and you will perceive that the thickest and lowest air will receive more light from the sun than the thinner air, because its beams meet with more resistance.
If the sky terminate low, at the end of a plain, that part of it nearest to the horizon, being seen only through the thick air, will alter and break its naturalcolour, and will appear whiter than over your head, where the visual ray does not pass through so much of that gross air, corrupted by earthy vapours. But if you turn towards the east, the air will be darker the nearer it approaches the earth; for the air being thicker, does not admit the light of the sun to pass so freely.
Itis evident that the air is in some parts thicker and grosser than in others, particularly that nearest to the earth; and as it rises higher, it becomes thinner and more transparent. The objects which are high and large, from which you are at some distance, will be less apparent in the lower parts; because the visual ray which perceives them, passes through a long space of dense air; and it is easy to prove that the upper parts are seen by a line, which, though on the side of the eye it originates in a thick air, nevertheless, as it ascends to the highest summit of its object, terminates in an air much thinner than that of the lower parts; and for that reason the more that line or visual ray advances from the eye, it becomes, in its progress from one point to another, thinner and thinner, passing from a pure air into another which is purer; so that a painter who has mountains to represent in a landscape, ought to observe, that from one hill to another, the tops will appear always clearer than the bases. In proportion as the distance from one to another is greater, the top will beclearer; and the higher they are, the more they will shew their variety of form and colour.
Theparts that are near in the fore-ground should be finished in a bold determined manner; but those in the distance must be unfinished, and confused in their outlines.
Thatpart of any object which is nearest to the luminary from which it receives the light, will be the lightest.
The representation of an object in every degree of distance, loses degrees of its strength; that is, in proportion as the object is more remote from the eye it will be less perceivable through the air in its representation.
Buildings in Thick Air
Thatpart of a building seen through a thick air, will appear less distinct than another part seen through a thinner air. Therefore the eye, N, looking at thetower A D, will see it more confusedly in the lower degrees, but at the same time lighter; and as it ascends to the other degrees it will appear more distinct, but somewhat darker.
Towns in Thick Air
Buildingsor towns seen through a fog, or the air made thick by smoke or other vapours, will appear less distinct the lower they are; and,vice versâ, they will be sharper and more visible in proportion as they are higher. We have said, in Chapter cccxxi. that the air is thicker the lower it is, and thinner as it is higher. It is demonstrated also by the cut, where the tower, A F, is seen by the eye N, in a thick air, from B to F, which is divided into four degrees, growing thicker as they are nearer the bottom. The less the quantity of air interposed between the eye and its object is, the less also will the colour of the object participate of the colour of that air. Itfollows, that the greater the quantity of the air interposed between the eye and the object seen, is, the more this object will participate of the colour of the air. It is demonstrated thus: N being the eye looking at the five parts of the tower A F, viz. A B C D E, I say, that if the air were of the same thickness, there would be the same proportion between the colour of the air at the bottom of the tower and the colour of the air that the same tower has at the place B, as there is in length between the line M and F. As, however, we have supposed that the air is not of equal thickness, but, on the contrary, thicker as it is lower, it follows, that the proportion by which the air tinges the different elevations of the tower B C F, exceeds the proportion of the lines; because the line M F, besides its being longer than the line S B, passes by unequal degrees through a quality of air which is unequal in thickness.
Theinferior or lower extremities of distant objects are not so apparent as the upper extremities. This is observable in mountains and hills, the tops of which detach from the sides of other mountains behind. We see the tops of these more determined and distinctly than their bases; because the upper extremities are darker, being less encompassed by thick air, which always remains in the lower regions, and makes them appear dim and confused. It is thesame with trees, buildings, and other objects high up. From this effect it often happens that a high tower, seen at a great distance, will appear broad at top, and narrow at bottom; because the thin air towards the top does not prevent the angles on the sides and other different parts of the tower from being seen, as the thick air does at bottom. This is demonstrated by the seventh proposition[77], which says, that the thick air interposed between the eye and the sun, is lighter below than above, and where the air is whiteish, it confuses the dark objects more than if such air were blueish or thinner, as it is higher up. The battlements of a fortress have the spaces between equal to the breadth of the battlement, and yet the space will appear wider; at a great distance the battlements will appear very much diminished, and being removed still farther, will disappear entirely, and the fort shew only the straight wall, as if there were no battlements.
Thesmallest parts are those which, by being removed, lose their appearance first; this may be observed in the gloss upon spherical bodies, or columns, and the slender parts of animals; as in a stag, the first sight of which does not discover its legs and horns so soon as its body, which, beingbroader, will be perceived from a greater distance. But the parts which disappear the very first, are the lines which describe the members, and terminate the surface and shape of bodies.
Thishappens because the smallest parts are lost first; the second, in point of size, are also lost at a somewhat greater distance, and so on successively; the parts by degrees melting away, the perception of the object is diminished; and at last all the parts, and the whole, are entirely lost to the sight[78]. Colours also disappear on account of the density of the air interposed between the eye and the object.
Itis evident that the similitude of all objects placed before us, large as well as small, is perceptible to our senses through the iris of the eye. If through so small an entrance the immensity of the sky and of the earth is admitted, the faces of men (which are scarcely any thing in comparison of such large objects), being still diminished by the distance, will occupy so little of the eye, that they become almost imperceptible. Besides, having to pass through a dark medium from the surface to theRetinain theinside, where the impression is made, the colour of faces (not being very strong, and rendered still more obscure by the darkness of the tube) when arrived at the focus appears dark. No other reason can be given on that point, except that the speck in the middle of the apple of the eye is black, and, being full of a transparent fluid like air, performs the same office as a hole in a board, which on looking into it appears black; and that those things which are seen through both a light and dark air, become confused and obscure.
Buildingsseen afar off in the morning or in the evening, when there is a fog, or thick air, shew only those parts distinctly which are enlightened by the sun towards the horizon; and the parts of those buildings which are not turned towards the sun remain confused and almost of the colour of the fog.
Ofa building near the eye the top parts will appear more confused than the bottom, because there is more fog between the eye and the top than at the base. And a square tower, seen at a great distance through a fog, will appear narrower at the base than at the summit. This is accounted for in Chapter cccxiii. which says, that the fog will appear whiter and thicker as it approaches the ground;and as it is said before[79], that a dark object will appear smaller in proportion as it is placed on a whiter ground. Therefore the fog being whiter at bottom than at top, it follows that the tower (being darkish) will appear narrower at the base than at the summit.
Amongstobjects situated in a fog, thick air, vapour, smoke, or at a distance, the highest will be the most distinctly seen: and amongst objects equal in height, that placed in the darkest fog, will be most confused and dark. As it happens to the eye H, looking at A B C, three towers of equal height; it sees the top C as low as R, in two degrees of thickness; and the top B, in one degree only; therefore the top C will appear darker than the top of the tower B.
High Objects Darker
Objectsseen through a fog will appear larger than they are in reality, because the aerial perspective does not agree with the linear, viz. the colour does not agree with the magnitude of the object[80]; such a fog being similar to the thickness of air interposed between the eye and the horizon in fine weather. But in this case the fog is near the eye, and though the object be also near, it makes it appear as if it were as far off as the horizon; where a great tower would appear no bigger than a man placed near the eye.
Thenearer the air is to water, or to the ground, the thicker it becomes. It is proved by the nineteenth proposition of the second book[81], that bodies rise in proportion to their weight; and it follows, that a light body will rise higher than another which is heavy.
Ofdifferent objects equal in magnitude, form, shade, and distance from the eye, those will appear the smaller that are placed on the lighter ground. This is exemplified by observing the sun when seen behind a tree without leaves; all the ramifications seen against that great light are so diminished that they remain almost invisible. The same may be observed of a pole placed between the sun and the eye.
Parallel bodies placed upright, and seen through a fog, will appear larger at top than at bottom. This is proved by the ninth proposition[82], which says, that a fog, or thick air, penetrated by the rays of the sun, will appear whiter the lower they are.
Things seen afar off will appear out of proportion, because the parts which are the lightest will send their image with stronger rays than the parts which are darkest. I have seen a woman dressed in black, with a white veil over her head, which appeared twice as large as her shoulders covered with black.
Anydark object will appear lighter when removed to some distance from the eye. It follows, by the contrary reason, that a dark object will appear still darker when brought nearer to the eye. Therefore the inferior parts of any object whatever, placed in thick air, will appear farther from the eye at the bottom than at the top; for that reason the lower parts of a mountain appear farther off than its top, which is in reality the farthest.
Theeye which, looking downwards, sees a town immersed in very thick air, will perceive the top of the buildings darker, but more distinct than the bottom. The tops detach against a light ground, because they are seen against the low and thick air which is beyond them. This is a consequence of what has been explained in the preceding chapter.
Contrivethat the trees in your landscape be half in shadow and half in the light. It is better to represent them as when the sun is veiled with thin clouds, because in that case the trees receive a general light from the sky, and are darkest in those parts which are nearest to the earth.
Ofthe greens seen in the country, that of trees and other plants will appear darker than that of fields and meadows, though they may happen to be of the same quality.
Thosegreens will appear to approach nearest to blue which are of the darkest shade when remote. This is proved by the seventh proposition[83], which says, that blue is composed of black and white seen at a great distance.
Whenthe sea is a little ruffled it has no sameness of colour; for whoever looks at it from the shore, will see it of a dark colour, in a greater degree as itapproaches towards the horizon, and will perceive also certain lights moving slowly on the surface like a flock of sheep. Whoever looks at the sea from on board a ship, at a distance from the land, sees it blue. Near the shore it appears darkish, on account of the colour of the earth reflected by the water, as in a looking-glass; but at sea the azure of the air is reflected to the eye by the waves in the same manner.
Objectsin the country appear sometimes larger and sometimes smaller than they actually are, from the circumstance of the air interposed between the eye and the horizon, happening to be either thicker or thinner than usual.
Of two horizons equally distant from the eye, that which is seen through the thicker air will appear farther removed; and the other will seem nearer, being seen through a thinner air.
Objects of unequal size, but equally distant, will appear equal if the air which is between them and the eye be of proportionable inequality of thickness, viz. if the thickest air be interposed between the eye and the smallest of the objects. This is proved by the perspective of colours[84], which is so deceitful that a mountain which would appear small by the compasses, will seem larger than a small hill nearthe eye; as a finger placed near the eye will cover a large mountain far off.
Smokeis more transparent, though darker towards the extremities of its waves than in the middle.
It moves in a more oblique direction in proportion to the force of the wind which impels it.
Different kinds of smoke vary in colour, as the causes that produce them are various.
Smoke never produces determined shadows, and the extremities are lost as they recede from their primary cause. Objects behind it are less apparent in proportion to the thickness of the smoke. It is whiter nearer its origin, and bluer towards its termination.
Fire appears darker, the more smoke there is interposed between it and the eye.
Where smoke is farther distant, the objects are less confused by it.
It encumbers and dims all the landscape like a fog. Smoke is seen to issue from different places, with flames at the origin, and the most dense part of it. The tops of mountains will be more seen than the lower parts, as in a fog.
Smokewhich is seen between the sun and the eye will be lighter and more transparent than any otherin the landscape. The same is observed of dust, and of fog; while, if you place yourself between the sun and those objects, they will appear dark.
Thesun-beams which penetrate the openings interposed between clouds of various density and form, illuminate all the places over which they pass, and tinge with their own colour all the dark places that are behind: which dark places are only seen in the intervals between the rays.
Whenthe rain begins to fall, it tarnishes and darkens the air, giving it a dull colour, but receives still on one side a faint light from the sun, and is shaded on the other side, as we observe in clouds; till at last it darkens also the earth, depriving it entirely of the light of the sun. Objects seen through the rain appear confused and of undetermined shape, but those which are near will be more distinct. It is observable, that on the side where the rain is shaded, objects will be more clearly distinguished than where it receives the light; because on the shady side they lose only their principal lights, whilst on the other they lose both their lights and shadows, the lights mixing with the light part of the rain, and the shadows are also considerably weakened by it.
InAutumn you will represent the objects according as it is more or less advanced. At the beginning of it the leaves of the oldest branches only begin to fade, more or less, however, according as the plant is situated in a fertile or barren country; and do not imitate those who represent trees of every kind (though at equal distance) with the same quality of green. Endeavour to vary the colour of meadows, stones, trunks of trees, and all other objects, as much as possible, for Nature abounds in varietyad infinitum.
Nearthe sea-shore, and in southern parts, you will be careful not to represent the Winter season by the appearance of trees and fields, as you would do in places more inland, and in northern countries, except when these are covered with ever-greens, which shoot afresh all the year round.
Dustbecomes lighter the higher it rises, and appears darker the less it is raised, when it is seen between the eye and the sun.
Inrepresenting the effect of the wind, besides the bending of trees, and leaves twisting the wrong side upwards, you will also express the small dust whirling upwards till it mixes in a confused manner with the air.
Thosetrees and shrubs which are by their nature more loaded with small branches, ought to be touched smartly in the shadows, but those which have larger foliage, will cause broader shadows.
Bythe sixth proposition[85], the horizon will be seen in the water as in a looking-glass, on that side which is opposite the eye. And if the painter has to represent a spot covered with water, let him remember that the colour of it cannot be either lighter or darker than that of the neighbouring objects.
Theshadows of bridges can never be seen on the surface of the water, unless it should have lost its transparent and reflecting quality, and become troubledand muddy; because clear water being polished and smooth on its surface, the image of the bridge is formed in it as in a looking-glass, and reflected in all the points situated between the eye and the bridge at equal angles; and even the air is seen under the arches. These circumstances cannot happen when the water is muddy, because it does not reflect the objects any longer, but receives the shadow of the bridge in the same manner as a dusty road would receive it.
Toput in practice that perspective which teaches the alteration, the lessening, and even the entire loss of the very essence of colours, you must take some points in the country at the distance of about sixty-five yards[86]from each other; as trees, men, or some other remarkable objects. In regard to the first tree, you will take a glass, and having fixed that well, and also your eye, draw upon it, with the greatest accuracy, the tree you see through it; then put it a little on one side, and compare it closely with the natural one, and colour it, so that in shape and colour it may resemble the original, and that by shutting one eye they may both appear painted, and at the same distance. The same rule may be applied to the second and third tree at the distance you have fixed. Thesestudies will be very useful if managed with judgment, where they may be wanted in the offscape of a picture. I have observed that the second tree is less by four fifths than the first, at the distance of thirteen yards.
Thesuperficies of any opake body participates of the colour of the transparent medium interposed between the eye and such body, in a greater or less degree, in proportion to the density of such medium and the space it occupies.
The outlines of opake bodies will be less apparent in proportion as those bodies are farther distant from the eye.
That part of the opake body will be the most shaded, or lightest, which is nearest to the body that shades it, or gives it light.
The surface of any opake body participates more or less of the colour of that body which gives it light, in proportion as the latter is more or less remote, or more or less strong.
Objects seen between lights and shadows will appear to have greater relievo than those which are placed wholly in the light, or wholly in shadow.
When you give strength and precision to objects seen at a great distance, they will appear as if they were very near. Endeavour that your imitation be such as to give a just idea of distances. If the objectin nature appear confused in the outlines, let the same be observed in your picture.
The outlines of distant objects appear undetermined and confused, for two reasons: the first is, that they come to the eye by so small an angle, and are therefore so much diminished, that they strike the sight no more than small objects do, which though near can hardly be distinguished, such as the nails of the fingers, insects, and other similar things: the second is, that between the eye and the distant objects there is so much air interposed, that it becomes thick; and, like a veil, tinges the shadows with its own whiteness, and turns them from a dark colour to another between black and white, such as azure.
Although, by reason of the great distance, the appearance of many things is lost, yet those things which receive the light from the sun will be more discernible, while the rest remain enveloped in confused shadows. And because the air is thicker near the ground, the things which are lower will appear confused; andvice versâ.
When the sun tinges the clouds on the horizon with red, those objects which, on account of their distance, appear blueish, will participate of that redness, and will produce a mixture between the azure and red, which renders the prospect lively and pleasant; all the opake bodies which receive that light will appear distinct, and of a reddish colour, and the air, being transparent, will be impregnated with it, and appear of the colour of lilies[87].
The air which is between the earth and the sun when it rises or sets, will always dim the objects it surrounds, more than the air any where else, because it is whiter.
It is not necessary to mark strongly the outlines of any object which is placed upon another. It ought to detach of itself.
If the outline or extremity of a white and curved surface terminate upon another white body, it will have a shade at that extremity, darker than any part of the light; but if against a dark object, such outline, or extremity, will be lighter than any part of the light.
Those objects which are most different in colour, will appear the most detached from each other.
Those parts of objects which first disappear in the distance, are extremities similar in colour, and ending one upon the other, as the extremities of an oak tree upon another oak similar to it. The next to disappear at a greater distance are, objects of mixed colours, when they terminate one upon the other, as trees, ploughed fields, walls, heaps of rubbish, or of stones. The last extremities of bodies that vanish are those which, being light, terminate upon a dark ground; or being dark, upon a light ground.
Of objects situated above the eye, at equal heights, the farthest removed from the eye will appear the lowest; and if situated below the eye, the nearest to it will appear the lowest. The parallel lines situated sidewise will concur to one point[88].
Those objects which are near a river, or a lake, in the distant part of a landscape, are less apparent and distinct than those that are remote from them.
Of bodies of equal density, those that are nearest to the eye will appear thinnest, and the most remote thickest.
A large eye-ball will see objects larger than a small one. The experiment may be made by looking at any of the celestial bodies, through a pin-hole, which being capable of admitting but a portion of its light, it seems to diminish and lose of its size in the same proportion as the pin-hole is smaller than the usual apparent size of the object.
A thick air interposed between the eye and any object, will render the outlines of such object undetermined and confused, and make it appear of a larger size than it is in reality; because the linear perspective does not diminish the angle which conveys the object to the eye. The aerial perspective carries it farther off, so that the one removes it from the eye, while the other preserves its magnitude[89].
When the sun is in the West the vapours of the earth fall down again and thicken the air, so that objects not enlightened by the sun remain dark and confused, but those which receive its light will be tinged yellow and red, according to the sun’s appearance on the horizon. Again, those that receive its light are very distinct, particularly public buildingsand houses in towns and villages, because their shadows are dark, and it seems as if those parts which are plainly seen were coming out of confused and undetermined foundations, because at that time every thing is of one and the same colour, except what is enlightened by the sun[90].
Any object receiving the light from the sun, receives also the general light; so that two kinds of shadows are produced: the darkest of the two is that which happens to have its central line directed towards the centre of the sun. The central lines of the primitive and secondary lights are the same as the central lines of the primitive and secondary shadows.
The setting sun is a beautiful and magnificent object when it tinges with its colour all the great buildings of towns, villages, and the top of high trees in the country. All below is confused and almost lost in a tender and general mass; for, being only enlightened by the air, the difference between the shadows and the lights is small, and for that reason it is not much detached. But those that are high are touched by the rays of the sun, and, as was said before, are tinged with its colour; the painter therefore ought to take the same colour with which he has painted the sun, and employ it in all those parts of his work which receive its light.
It also happens very often, that a cloud will appeardark without receiving any shadow from a separate cloud, according to the situation of the eye; because it will see only the shady part of the one, while it sees both the enlightened and shady parts of the other.
Of two objects at equal height, that which is the farthest off will appear the lowest. Observe the first cloud in the cut, though it is lower than the second, it appears as if it were higher. This is demonstrated by the section of the pyramidical rays of the low cloud at M A, and the second (which is higher) at N M, below M A. This happens also when, on account of the rays of the setting or rising sun, a dark cloud appears higher than another which is light.