Part 14

/The/ air will participate less of the azure of the sky, in proportion as it comes nearer to the horizon, as it is proved by the third and ninth proposition[70], that pure and subtile bodies (such as compose the air) will be less illuminated by the sun than those of thicker and grosser substance: and as it is certain that the air which is remote from the earth, is thinner than that which is near it, it will follow, that the latter will be more impregnated with the rays of the sun, which giving light at the same time to an infinity of atoms floating in this air, renders it more sensible to the eye. So that the air will appear lighter towards the horizon, and darker as well as bluer in looking up to the sky; because there is more of the thick air between our eyes and the horizon, than between our eyes and that part of the sky above our heads.

For instance: if the eye placed in P, looks through the air along the line P R, and then lowers itself a little along P S, the air will begin to appear a little whiter, because there is more of the thick air in this space than in the first. And if it be still removed lower, so as to look straight at the horizon, no more of that blue sky will be perceived which was observable along the first line P R, because there is a much greater quantity of thick air along the horizontal line P D, than along the oblique P S, or the perpendicular P R.

/Chap. CCLXXXV./--_The Cause of the Diminution of Colours._

/The/ natural colour of any visible object will be diminished in proportion to the density of any other substance which interposes between that object and the eye.

/Chap. CCLXXXVI./--_Of the Diminution of Colours and Objects._

/Let/ the colours vanish in proportion as the objects diminish in size, according to the distance.

/Chap. CCLXXXVII./--_Of the Variety observable in Colours, according to their Distance, or Proximity._

/The/ local colour of such objects as are darker than the air, will appear less dark as they are more remote; and, on the contrary, objects lighter than the air will lose their brightness in proportion to their distance from the eye. In general, all objects that are darker or lighter than the air, are discoloured by distance, which changes their quality, so that the lighter appears darker, and the darker lighter.

/Chap. CCLXXXVIII./--_At what Distance Colours are entirely lost._

/Local/ colours are entirely lost at a greater or less distance, according as the eye and the object are more or less elevated from the earth. This is proved by the seventh proposition[71], which says, the air is more or less pure, as it is near to, or remote from the earth. If the eye then, and the object are near the earth, the thickness of the air which interposes, will in a great measure confuse the colour of that object to the eye. But if the eye and the object are placed high above the earth, the air will disturb the natural colour of that object very little. In short, the various gradations of colour depend not only on the various distances, in which they may be lost; but also on the variety of lights, which change according to the different hours of the day, and the thickness or purity of the air, through which the colour of the object is conveyed to the eye.

/Chap. CCLXXXIX./--_Of the Change observable in the same Colour, according to its Distance from the Eye._

/Among/ several colours of the same nature, that which is the nearest to the eye will alter the least; because the air which interposes between the eye and the object seen, envelopes, in some measure, that object. If the air, which interposes, be in great quantity, the object seen will be strongly tinged with the colour of that air; but if the air be thin, then the view of that object, and its colour, will be very little obstructed.

/Chap. CCXC./--_Of the blueish Appearance of remote Objects in a Landscape._

/Whatever/ be the colour of distant objects, the darkest, whether natural or accidental, will appear the most tinged with azure. By the natural darkness is meant the proper colour of the object; the accidental one is produced by the shadow of some other body.

/Chap. CCXCI./--_Of the Qualities in the Surface which first lose themselves by Distance._

/The/ first part of any colour which is lost by the distance, is the gloss, being the smallest part of it, as a light within a light. The second that diminishes by being farther removed, is the light, because it is less in quantity than the shadow. The third is the principal shadows, nothing remaining at last but a kind of middling obscurity.

/Chap. CCXCII./--_From what Cause the Azure of the Air proceeds._

/The/ azure of the sky is produced by the transparent body of the air, illumined by the sun, and interposed between the darkness of the expanse above, and the earth below. The air in itself has no quality of smell, taste, or colour, but is easily impregnated with the quality of other matter surrounding it; and will appear bluer in proportion to the darkness of the space behind it, as may be observed against the shady sides of mountains, which are darker than any other object. In this instance the air appears of the most beautiful azure, while on the other side that receives the light, it shews through that more of the natural colour of the mountain.

/Chap. CCXCIII./--_Of the Perspective of Colours._

/The/ same colour being placed at various distances and equal elevation, the force and effect of its colouring will be according to the proportion of the distance which there is from each of these colours to the eye. It is proved thus: let C B E D be one and the same colour. The first, E, is placed at two degrees of distance from the eye A; the second, B, shall be four degrees, the third, C, six degrees, and the fourth, D, eight degrees; as appears by the circles which terminate upon and intersect the line A R. Let us suppose that the space A R, S P, is one degree of thin air, and S P E T another degree of thicker air. It will follow, that the first colour, E, will pass to the eye through one degree of thick air, E S, and through another degree, S A, of thinner air. And B will send its colour to the eye in A, through two degrees of thick air, and through two others of the thinner sort. C will send it through three degrees of the thin, and three of the thick sort, while D goes through four degrees of the one, and four of the other. This demonstrates, that the gradation of colours is in proportion to their distance from the eye[72]. But this happens only to those colours which are on a level with the eye; as for those which happen to be at unequal elevations, we cannot observe the same rule, because they are in that case situated in different qualities of air, which alter and diminish these colours in various manners.

/Chap. CCXCIV./--_Of the Perspective of Colours in dark Places._

/In/ any 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.

/Chap. CCXCV./--_Of the Perspective of Colours._

/The/ principal 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.

/Chap. CCXCVI./--_Of Colours._

/Of/ all 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.

/Chap. CCXCVII./--_How it happens that Colours do not change, though placed in different Qualities of Air._

/The/ colour 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.

/Chap. CCXCVIII./--_Why Colours experience no apparent Change, though placed in different Qualities of Air._

/It/ may 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 the eye, 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: reckoning first 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.

/Chap. CCXCIX./--_Contrary Opinions in regard to Objects seen afar off._

/Many/ painters 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.

/Chap. CCC./--_Of the Colour of Objects remote from the Eye._

/The/ air 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, and conveyed 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.

/Chap. CCCI./--_Of the Colour of Mountains._

/The/ darker 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.

/Chap. CCCII./--_Why the Colour and Shape of Objects are lost in some Situations apparently dark, though not so in Reality._

/There/ are some situations which, though light, appear dark, and in which objects are deprived both of 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].

/Chap. CCCIII./--_Various Precepts in Painting._

/The/ termination 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, and _vice 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.

AERIAL PERSPECTIVE.

/Chap. CCCIV./--_Aerial Perspective._

/There/ is 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.

/Chap. CCCV./--_The Parts of the Smallest Objects will first disappear in Painting._

/Of/ objects 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.

/Chap. CCCVI./--_Small Figures ought not to be too much finished._

/Objects/ appear 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.

/Chap. CCCVII./--_Why the Air is to appear whiter as it approaches nearer to the Earth._

/As/ the 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 natural colour, 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.

/Chap. CCCVIII./--_How to paint the distant Part of a Landscape._

/It/ is 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 be clearer; and the higher they are, the more they will shew their variety of form and colour.

/Chap. CCCIX./--_Of precise and confused Objects._

/The/ parts 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.

/Chap. CCCX./--_Of distant Objects._

/That/ part of any object which is nearest to the luminary from which it receives the light, will be the lightest.