4. This diagram below should end at _a n_ 4 8. [4]That portion of

the illuminated surface on which a shadow is cast will be brightest which lies contiguous to the cast shadow. Just as an object which is lighted up by a greater quantity of luminous rays becomes brighter, so one on which a greater quantity of shadow falls, will be darker. Let 4 be the side of an illuminated surface 4 8, surrounding the cast shadow _g e_ 4. And this spot 4 will be lighter than 8, because less shadow falls on it than on 8. Since 4 faces only the shadow _i n_; and 8 faces and receives the shadow _a e_ as well as _i n_ which makes it twice as dark. And the same thing happens when you put the atmosphere and the sun in the place of shade and light. [12] The distribution of shadow, originating in, and limited by, plane surfaces placed near to each other, equal in tone and directly opposite, will be darker at the ends than at the beginning, which will be determined by the incidence of the luminous rays. You will find the same proportion in the depth of the derived shadows _a n_ as in the nearness of the luminous bodies _m b_, which cause them; and if the luminous bodies were of equal size you would still farther find the same proportion in the light cast by the luminous circles and their shadows as in the distance of the said luminous bodies. [Footnote: The diagram originally placed between lines 3 and 4 is on Pl. VI, No. 3. In the diagram given above line 14 of the original, and here printed in the text, the words _corpo luminoso_ [luminous body] are written in the circle _m_, _luminoso_ in the circle _b_ and _ombroso_ [body in shadow] in the circle _o_.] 217. THAT PART OF THE REFLECTION WILL BE BRIGHTEST WHERE THE REFLECTED RAYS ARE SHORTEST. [2] The darkness occasioned by the casting of combined shadows will be in conformity with its cause, which will originate and terminate between two plane surfaces near together, alike in tone and directly opposite each other. [4] In proportion as the source of light is larger, the luminous and shadow rays will be more mixed together. This result is produced because wherever there is a larger quantity of luminous rays, there is most light, but where there are fewer there is least light, consequently the shadow rays come in and mingle with them. [Footnote: Diagrams are inserted before lines 2 and 4.] 218. In all the proportions I lay down it must be understood that the medium between the bodies is always the same. [2] The smaller the luminous body the more distinct will the transmission of the shadows be. [3] When of two opposite shadows, produced by the same body, one is twice as dark as the other though similar in form, one of the two lights causing them must have twice the diameter that the other has and be at twice the distance from the opaque body. If the object is lowly moved across the luminous body, and the shadow is intercepted at some distance from the object, there will be the same relative proportion between the motion of the derived shadow and the motion of the primary shadow, as between the distance from the object to the light, and that from the object to the spot where the shadow is intercepted; so that though the object is moved slowly the shadow moves fast. [Footnote: There are diagrams inserted before lines 2 and 3 but they are not reproduced here. The diagram above line 6 is written upon as follows: at _A lume_ (light), at _B obbietto_ (body), at _C ombra d'obbietto_ (shadow of the object).] 219. A luminous body will appear less brilliant when surrounded by a bright background. [2] I have found that the stars which are nearest to the horizon look larger than the others because light falls upon them from a larger proportion of the solar body than when they are above us; and having more light from the sun they give more light, and the bodies which are most luminous appear the largest. As may be seen by the sun through a mist, and overhead; it appears larger where there is no mist and diminished through mist. No portion of the luminous body is ever visible from any spot within the pyramid of pure derived shadow. [Footnote: Between lines 1 and 2 there is in the original a large diagram which does not refer to this text. ] 220. A body on which the solar rays fall between the thin branches of trees far apart will cast but a single shadow. [2] If an opaque body and a luminous one are (both) spherical the base of the pyramid of rays will bear the same proportion to the luminous body as the base of the pyramid of shade to the opaque body. [4] When the transmitted shadow is intercepted by a plane surface placed opposite to it and farther away from the luminous body than from the object [which casts it] it will appear proportionately darker and the edges more distinct. [Footnote: The diagram which, in the original, is placed above line 2, is similar to the one, here given on page 73 (section 120).--The diagram here given in the margin stands, in the original, between lines 3 and 4.] 221. A body illuminated by the solar rays passing between the thick branches of trees will produce as many shadows as there are branches between the sun and itself. Where the shadow-rays from an opaque pyramidal body are intercepted they will cast a shadow of bifurcate outline and various depth at the points. A light which is broader than the apex but narrower than the base of an opaque pyramidal body placed in front of it, will cause that pyramid to cast a shadow of bifurcate form and various degrees of depth. If an opaque body, smaller than the light, casts two shadows and if it is the same size or larger, casts but one, it follows that a pyramidal body, of which part is smaller, part equal to, and part larger than, the luminous body, will cast a bifurcate shadow. [Footnote: Between lines 2 and 3 there are in the original two large diagrams.] _IV._ _Perspective of Disappearance._ _The theory of the_ "Prospettiva de' perdimenti" _would, in many important details, be quite unintelligible if it had not been led up by the principles of light and shade on which it is based. The word_ "Prospettiva" _in the language of the time included the principles of optics; what Leonardo understood by_ "Perdimenti" _will be clearly seen in the early chapters, Nos._ 222--224. _It is in the very nature of the case that the farther explanations given in the subsequent chapters must be limited to general rules. The sections given as_ 227--231 _"On indistinctness at short distances" have, it is true, only an indirect bearing on the subject; but on the other hand, the following chapters,_ 232--234, _"On indistinctness at great distances," go fully into the matter, and in chapters_ 235--239, _which treat "Of the importance of light and shade in the Perspective of Disappearance", the practical issues are distinctly insisted on in their relation to the theory. This is naturally followed by the statements as to "the effect of light or dark backgrounds on the apparent size of bodies"_ (_Nos._ 240--250). _At the end I have placed, in the order of the original, those sections from the MS._ C _which treat of the "Perspective of Disappearance" and serve to some extent to complete the treatment of the subject_ (251--262). Definition (222. 223). 222. OF THE DIMINISHED DISTINCTNESS OF THE OUTLINES OF OPAQUE BODIES. If the real outlines of opaque bodies are indistinguishable at even a very short distance, they will be more so at long distances; and, since it is by its outlines that we are able to know the real form of any opaque body, when by its remoteness we fail to discern it as a whole, much more must we fail to discern its parts and outlines. 223. OF THE DIMINUTION IN PERSPECTIVE OF OPAQUE OBJECTS. Among opaque objects of equal size the apparent diminution of size will be in proportion to their distance from the eye of the spectator; but it is an inverse proportion, since, where the distance is greater, the opaque body will appear smaller, and the less the distance the larger will the object appear. And this is the fundamental principle of linear perspective and it follows:--[11]every object as it becomes more remote loses first those parts which are smallest. Thus of a horse, we should lose the legs before the head, because the legs are thinner than the head; and the neck before the body for the same reason. Hence it follows that the last part of the horse which would be discernible by the eye would be the mass of the body in an oval form, or rather in a cylindrical form and this would lose its apparent thickness before its length--according to the 2nd rule given above, &c. [Footnote 23: Compare line 11.]. If the eye remains stationary the perspective terminates in the distance in a point. But if the eye moves in a straight [horizontal] line the perspective terminates in a line and the reason is that this line is generated by the motion of the point and our sight; therefore it follows that as we move our sight [eye], the point moves, and as we move the point, the line is generated, &c. An illustration by experiment. 224. Every visible body, in so far as it affects the eye, includes three attributes; that is to say: mass, form and colour; and the mass is recognisable at a greater distance from the place of its actual existence than either colour or form. Again, colour is discernible at a greater distance than form, but this law does not apply to luminous bodies. The above proposition is plainly shown and proved by experiment; because: if you see a man close to you, you discern the exact appearance of the mass and of the form and also of the colouring; if he goes to some distance you will not recognise who he is, because the character of the details will disappear, if he goes still farther you will not be able to distinguish his colouring, but he will appear as a dark object, and still farther he will appear as a very small dark rounded object. It appears rounded because distance so greatly diminishes the various details that nothing remains visible but the larger mass. And the reason is this: We know very well that all the images of objects reach the senses by a small aperture in the eye; hence, if the whole horizon _a d_ is admitted through such an aperture, the object _b c_ being but a very small fraction of this horizon what space can it fill in that minute image of so vast a hemisphere? And because luminous bodies have more power in darkness than any others, it is evident that, as the chamber of the eye is very dark, as is the nature of all colored cavities, the images of distant objects are confused and lost in the great light of the sky; and if they are visible at all, appear dark and black, as every small body must when seen in the diffused light of the atmosphere. [Footnote: The diagram belonging to this passage is placed between lines 5 and 6; it is No. 4 on Pl. VI. ] A guiding rule. 225. OF THE ATMOSPHERE THAT INTERPOSES BETWEEN THE EYE AND VISIBLE OBJECTS. An object will appear more or less distinct at the same distance, in proportion as the atmosphere existing between the eye and that object is more or less clear. Hence, as I know that the greater or less quantity of the air that lies between the eye and the object makes the outlines of that object more or less indistinct, you must diminish the definiteness of outline of those objects in proportion to their increasing distance from the eye of the spectator. An experiment. 226. When I was once in a place on the sea, at an equal distance from the shore and the mountains, the distance from the shore looked much greater than that from the mountains. On indistinctness at short distances (227-231). 227. If you place an opaque object in front of your eye at a distance of four fingers' breadth, if it is smaller than the space between the two eyes it will not interfere with your seeing any thing that may be beyond it. No object situated beyond another object seen by the eye can be concealed by this [nearer] object if it is smaller than the space from eye to eye. 228. The eye cannot take in a luminous angle which is too close to it. 229. That part of a surface will be better lighted on which the light falls at the greater angle. And that part, on which the shadow falls at the greatest angle, will receive from those rays least of the benefit of the light. 230. OF THE EYE. The edges of an object placed in front of the pupil of the eye will be less distinct in proportion as they are closer to the eye. This is shown by the edge of the object _n_ placed in front of the pupil _d_; in looking at this edge the pupil also sees all the space _a c_ which is beyond the edge; and the images the eye receives from that space are mingled with the images of the edge, so that one image confuses the other, and this confusion hinders the pupil from distinguishing the edge. 231. The outlines of objects will be least clear when they are nearest to the eye, and therefore remoter outlines will be clearer. Among objects which are smaller than the pupil of the eye those will be less distinct which are nearer to the eye. On indistinctness at great distances (232-234). 232. Objects near to the eye will appear larger than those at a distance. Objects seen with two eyes will appear rounder than if they are seen with only one. Objects seen between light and shadow will show the most relief. 233. OF PAINTING. Our true perception of an object diminishes in proportion as its size is diminished by distance. 234. PERSPECTIVE. Why objects seen at a distance appear large to the eye and in the image on the vertical plane they appear small. PERSPECTIVE. I ask how far away the eye can discern a non-luminous body, as, for instance, a mountain. It will be very plainly visible if the sun is behind it; and could be seen at a greater or less distance according to the sun's place in the sky. [Footnote: The clue to the solution of this problem (lines 1-3) is given in lines 4-6, No. 232. Objects seen with both eyes appear solid since they are seen from two distinct points of sight separated by the distance between the eyes, but this solidity cannot be represented in a flat drawing. Compare No. 535.] The importance of light and shade in the perspective of disappearance (235-239). 235. An opaque body seen in a line in which the light falls will reveal no prominences to the eye. For instance, let _a_ be the solid body and _c_ the light; _c m_ and _c n_ will be the lines of incidence of the light, that is to say the lines which transmit the light to the object _a_. The eye being at the point _b_, I say that since the light _c_ falls on the whole part _m n_ the portions in relief on that side will all be illuminated. Hence the eye placed at _c_ cannot see any light and shade and, not seeing it, every portion will appear of the same tone, therefore the relief in the prominent or rounded parts will not be visible. 236. OF PAINTING. When you represent in your work shadows which you can only discern with difficulty, and of which you cannot distinguish the edges so that you apprehend them confusedly, you must not make them sharp or definite lest your work should have a wooden effect. 237. OF PAINTING. You will observe in drawing that among the shadows some are of undistinguishable gradation and form, as is shown in the 3rd [proposition] which says: Rounded surfaces display as many degrees of light and shade as there are varieties of brightness and darkness reflected from the surrounding objects. 238. OF LIGHT AND SHADE. You who draw from nature, look (carefully) at the extent, the degree, and the form of the lights and shadows on each muscle; and in their position lengthwise observe towards which muscle the axis of the central line is directed. 239. An object which is [so brilliantly illuminated as to be] almost as bright as light will be visible at a greater distance, and of larger apparent size than is natural to objects so remote. The effect of light or dark backgrounds on the apparent size of objects (240-250). 240. A shadow will appear dark in proportion to the brilliancy of the light surrounding it and conversely it will be less conspicuous where it is seen against a darker background. 241. OF ORDINARY PERSPECTIVE. An object of equal breadth and colour throughout, seen against a background of various colours will appear unequal in breadth. And if an object of equal breadth throughout, but of various colours, is seen against a background of uniform colour, that object will appear of various breadth. And the more the colours of the background or of the object seen against the ground vary, the greater will the apparent variations in the breadth be though the objects seen against the ground be of equal breadth [throughout]. 242. A dark object seen against a bright background will appear smaller than it is. A light object will look larger when it is seen against a background darker than itself. 243. OF LIGHT. A luminous body when obscured by a dense atmosphere will appear smaller; as may be seen by the moon or sun veiled by mists. OF LIGHT. Of several luminous bodies of equal size and brilliancy and at an equal distance, that will look the largest which is surrounded by the darkest background. OF LIGHT. I find that any luminous body when seen through a dense and thick mist diminishes in proportion to its distance from the eye. Thus it is with the sun by day, as well as the moon and the other eternal lights by night. And when the air is clear, these luminaries appear larger in proportion as they are farther from the eye. 244. That portion of a body of uniform breadth which is against a lighter background will look narrower [than the rest]. [4] _e_ is a given object, itself dark and of uniform breadth; _a b_ and _c d_ are two backgrounds one darker than the other; _b c_ is a bright background, as it might be a spot lighted by the sun through an aperture in a dark room. Then I say that the object _e g_ will appear larger at _e f_ than at _g h_; because _e f_ has a darker background than _g h_; and again at _f g_ it will look narrower from being seen by the eye _o_, on the light background _b c_. [Footnote 12: The diagram to which the text, lines 1-11, refers, is placed in the original between lines 3 and 4, and is given on Pl. XLI, No. 3. Lines 12 to 14 are explained by the lower of the two diagrams on Pl. XLI, No. 4. In the original these are placed after line 14.] That part of a luminous body, of equal breadth and brilliancy throughout, will look largest which is seen against the darkest background; and the luminous body will seem on fire. 245. WHY BODIES IN LIGHT AND SHADE HAVE THEIR OUTLINES ALTERED BY THE COLOUR AND BRIGHTNESS OF THE OBJECTS SERVING AS A BACKGROUND TO THEM. If you look at a body of which the illuminated portion lies and ends against a dark background, that part of the light which will look brightest will be that which lies against the dark [background] at _d_. But if this brighter part lies against a light background, the edge of the object, which is itself light, will be less distinct than before, and the highest light will appear to be between the limit of the background _m f_ and the shadow. The same thing is seen with regard to the dark [side], inasmuch as that edge of the shaded portion of the object which lies against a light background, as at _l_, it looks much darker than the rest. But if this shadow lies against a dark background, the edge of the shaded part will appear lighter than before, and the deepest shade will appear between the edge and the light at the point _o_. [Footnote: In the original diagram _o_ is inside the shaded surface at the level of _d_.] 246. An opaque body will appear smaller when it is surrounded by a highly luminous background, and a light body will appear larger when it is seen against a darker background. This may be seen in the height of buildings at night, when lightning flashes behind them; it suddenly seems, when it lightens, as though the height of the building were diminished. For the same reason such buildings look larger in a mist, or by night than when the atmosphere is clear and light. 247. ON LIGHT BETWEEN SHADOWS When you are drawing any object, remember, in comparing the grades of light in the illuminated portions, that the eye is often deceived by seeing things lighter than they are. And the reason lies in our comparing those parts with the contiguous parts. Since if two [separate] parts are in different grades of light and if the less bright is conterminous with a dark portion and the brighter is conterminous with a light background--as the sky or something equally bright--, then that which is less light, or I should say less radiant, will look the brighter and the brighter will seem the darker. 248. Of objects equally dark in themselves and situated at a considerable and equal distance, that will look the darkest which is farthest above the earth. 249. TO PROVE HOW IT IS THAT LUMINOUS BODIES APPEAR LARGER, AT A DISTANCE, THAN THEY ARE. If you place two lighted candles side by side half a braccio apart, and go from them to a distance 200 braccia you will see that by the increased size of each they will appear as a single luminous body with the light of the two flames, one braccio wide. TO PROVE HOW YOU MAY SEE THE REAL SIZE OF LUMINOUS BODIES. If you wish to see the real size of these luminous bodies, take a very thin board and make in it a hole no bigger than the tag of a lace and place it as close to your eye as possible, so that when you look through this hole, at the said light, you can see a large space of air round it. Then by rapidly moving this board backwards and forwards before your eye you will see the light increase [and diminish]. Propositions on perspective of disappearance from MS. C. (250-262). 250. Of several bodies of equal size and equally distant from the eye, those will look the smallest which are against the lightest background. Every visible object must be surrounded by light and shade. A perfectly spherical body surrounded by light and shade will appear to have one side larger than the other in proportion as one is more highly lighted than the other. 251. PERSPECTIVE. No visible object can be well understood and comprehended by the human eye excepting from the difference of the background against which the edges of the object terminate and by which they are bounded, and no object will appear [to stand out] separate from that background so far as the outlines of its borders are concerned. The moon, though it is at a great distance from the sun, when, in an eclipse, it comes between our eyes and the sun, appears to the eyes of men to be close to the sun and affixed to it, because the sun is then the background to the moon. 252. A luminous body will appear more brilliant in proportion as it is surrounded by deeper shadow. [Footnote: The diagram which, in the original, is placed after this text, has no connection with it.] 253. The straight edges of a body will appear broken when they are conterminous with a dark space streaked with rays of light. [Footnote: Here again the diagrams in the original have no connection with the text.] 254. Of several bodies, all equally large and equally distant, that which is most brightly illuminated will appear to the eye nearest and largest. [Footnote: Here again the diagrams in the original have no connection with the text.] 255. If several luminous bodies are seen from a great distance although they are really separate they will appear united as one body. 256. If several objects in shadow, standing very close together, are seen against a bright background they will appear separated by wide intervals. 257. Of several bodies of equal size and tone, that which is farthest will appear the lightest and smallest. 258. Of several objects equal in size, brightness of background and length that which has the flattest surface will look the largest. A bar of iron equally thick throughout and of which half is red hot, affords an example, for the red hot part looks thicker than the rest. 259. Of several bodies of equal size and length, and alike in form and in depth of shade, that will appear smallest which is surrounded by the most luminous background. 260. DIFFERENT PORTIONS OF A WALL SURFACE WILL BE DARKER OR BRIGHTER IN PROPORTION AS THE LIGHT OR SHADOW FALLS ON THEM AT A LARGER ANGLE. The foregoing proposition can be clearly proved in this way. Let us say that _m q_ is the luminous body, then _f g_ will be the opaque body; and let _a e_ be the above-mentioned plane on which the said angles fall, showing [plainly] the nature and character of their bases. Then: _a_ will be more luminous than _b_; the base of the angle _a_ is larger than that of _b_ and it therefore makes a greater angle which will be _a m q_; and the pyramid _b p m_ will be narrower and _m o c_ will be still finer, and so on by degrees, in proportion as they are nearer to _e_, the pyramids will become narrower and darker. That portion of the wall will be the darkest where the breadth of the pyramid of shadow is greater than the breadth of the pyramid of light. At the point _a_ the pyramid of light is equal in strength to the pyramid of shadow, because the base _f g_ is equal to the base _r f_. At the point _d_ the pyramid of light is narrower than the pyramid of shadow by so much as the base _s f_ is less than the base _f g_. Divide the foregoing proposition into two diagrams, one with the pyramids of light and shadow, the other with the pyramids of light [only]. 261. Among shadows of equal depth those which are nearest to the eye will look least deep. 262. The more brilliant the light given by a luminous body, the deeper will the shadows be cast by the objects it illuminates. _V._ _Theory of colours._ _Leonardo's theory of colours is even more intimately connected with his principles of light and shade than his Perspective of Disappearance and is in fact merely an appendix or supplement to those principles, as we gather from the titles to sections_ 264, 267_, and _276_, while others again_ (_Nos._ 281, 282_) are headed_ Prospettiva. _A very few of these chapters are to be found in the oldest copies and editions of the Treatise on Painting, and although the material they afford is but meager and the connection between them but slight, we must still attribute to them a special theoretical value as well as practical utility--all the more so because our knowledge of the theory and use of colours at the time of the Renaissance is still extremely limited._ The reciprocal effects of colours on objects placed opposite each other (263-272). 263. OF PAINTING. The hue of an illuminated object is affected by that of the luminous body. 264. OF SHADOW. The surface of any opaque body is affected by the colour of surrounding objects. 265. A shadow is always affected by the colour of the surface on which it is cast. 266. An image produced in a mirror is affected by the colour of the mirror. 267. OF LIGHT AND SHADE. Every portion of the surface of a body is varied [in hue] by the [reflected] colour of the object that may be opposite to it. EXAMPLE. If you place a spherical body between various objects that is to say with [direct] sunlight on one side of it, and on the other a wall illuminated by the sun, which wall may be green or of any other colour, while the surface on which it is placed may be red, and the two lateral sides are in shadow, you will see that the natural colour of that body will assume something of the hue reflected from those objects. The strongest will be [given by] the luminous body; the second by the illuminated wall, the third by the shadows. There will still be a portion which will take a tint from the colour of the edges. 268. The surface of every opaque body is affected by the colour of the objects surrounding it. But this effect will be strong or weak in proportion as those objects are more or less remote and more or less strongly [coloured]. 269. OF PAINTING. The surface of every opaque body assumes the hues reflected from surrounding objects. The surface of an opaque body assumes the hues of surrounding objects more strongly in proportion as the rays that form the images of those objects strike the surface at more equal angles. And the surface of an opaque body assumes a stronger hue from the surrounding objects in proportion as that surface is whiter and the colour of the object brighter or more highly illuminated. 270. OF THE RAYS WHICH CONVEY THROUGH THE AIR THE IMAGES OF OBJECTS. All the minutest parts of the image intersect each other without interfering with each other. To prove this let _r_ be one of the sides of the hole, opposite to which let _s_ be the eye which sees the lower end _o_ of the line _n o_. The other extremity cannot transmit its image to the eye _s_ as it has to strike the end _r_ and it is the same with regard to _m_ at the middle of the line. The case is the same with the upper extremity _n_ and the eye _u_. And if the end _n_ is red the eye _u_ on that side of the holes will not see the green colour of _o_, but only the red of _n_ according to the 7th of this where it is said: Every form projects images from itself by the shortest line, which necessarily is a straight line, &c. [Footnote: 13. This probably refers to the diagram given under No. 66.] 271. OF PAINTING. The surface of a body assumes in some degree the hue of those around it. The colours of illuminated objects are reflected from the surfaces of one to the other in various spots, according to the various positions of those objects. Let _o_ be a blue object in full light, facing all by itself the space _b c_ on the white sphere _a b e d e f_, and it will give it a blue tinge, _m_ is a yellow body reflected onto the space _a b_ at the same time as _o_ the blue body, and they give it a green colour (by the 2nd [proposition] of this which shows that blue and yellow make a beautiful green &c.) And the rest will be set forth in the Book on Painting. In that Book it will be shown, that, by transmitting the images of objects and the colours of bodies illuminated by sunlight through a small round perforation and into a dark chamber onto a plane surface, which itself is quite white, &c. But every thing will be upside down. Combination of different colours in cast shadows. 272. That which casts the shadow does not face it, because the shadows are produced by the light which causes and surrounds the shadows. The shadow caused by the light _e_, which is yellow, has a blue tinge, because the shadow of the body _a_ is cast upon the pavement at _b_, where the blue light falls; and the shadow produced by the light _d_, which is blue, will be yellow at _c_, because the yellow light falls there and the surrounding background to these shadows _b c_ will, besides its natural colour, assume a hue compounded of yellow and blue, because it is lighted by the yellow light and by the blue light both at once. Shadows of various colours, as affected by the lights falling on them. That light which causes the shadow does not face it. [Footnote: In the original diagram we find in the circle _e_ "_giallo_" (yellow) and the cirle _d_ "_azurro"_ (blue) and also under the circle of shadow to the left "_giallo_" is written and under that to the right "_azurro_". In the second diagram where four circles are placed in a row we find written, beginning at the left hand, "_giallo_" (yellow), "_azurro_" (blue), "_verde_" (green), "_rosso_" (red).] The effect of colours in the camera obscura (273-274). 273. The edges of a colour(ed object) transmitted through a small hole are more conspicuous than the central portions. The edges of the images, of whatever colour, which are transmitted through a small aperture into a dark chamber will always be stronger than the middle portions. 274. OF THE INTERSECTIONS OF THE IMAGES IN THE PUPIL OF THE EYE. The intersections of the images as they enter the pupil do not mingle in confusion in the space where that intersection unites them; as is evident, since, if the rays of the sun pass through two panes of glass in close contact, of which one is blue and the other yellow, the rays, in penetrating them, do not become blue or yellow but a beautiful green. And the same thing would happen in the eye, if the images which were yellow or green should mingle where they [meet and] intersect as they enter the pupil. As this does not happen such a mingling does not exist. OF THE NATURE OF THE RAYS COMPOSED OF THE IMAGES OF OBJECTS, AND OF THEIR INTERSECTIONS. The directness of the rays which transmit the forms and colours of the bodies whence they proceed does not tinge the air nor can they affect each other by contact where they intersect. They affect only the spot where they vanish and cease to exist, because that spot faces and is faced by the original source of these rays, and no other object, which surrounds that original source can be seen by the eye where these rays are cut off and destroyed, leaving there the spoil they have conveyed to it. And this is proved by the 4th [proposition], on the colour of bodies, which says: The surface of every opaque body is affected by the colour of surrounding objects; hence we may conclude that the spot which, by means of the rays which convey the image, faces--and is faced by the cause of the image, assumes the colour of that object. On the colours of derived shadows (275. 276). 275. ANY SHADOW CAST BY AN OPAQUE BODY SMALLER THAN THE LIGHT CAUSING THE SHADOW WILL THROW A DERIVED SHADOW WHICH IS TINGED BY THE COLOUR OF THE LIGHT. Let _n_ be the source of the shadow _e f_; it will assume its hue. Let _o_ be the source of _h e_ which will in the same way be tinged by its hue and so also the colour of _v h_ will be affected by _p_ which causes it; and the shadow of the triangle _z k y_ will be affected by the colour of _q_, because it is produced by it. [7] In proportion as _c d_ goes into _a d_, will _n r s_ be darker than _m_; and the rest of the space will be shadowless [11]. _f g_ is the highest light, because here the whole light of the window _a d_ falls; and thus on the opaque body _m e_ is in equally high light; _z k y_ is a triangle which includes the deepest shadow, because the light _a d_ cannot reach any part of it. _x h_ is the 2nd grade of shadow, because it receives only 1/3 of the light from the window, that is _c d_. The third grade of shadow is _h e_, where two thirds of the light from the window is visible. The last grade of shadow is _b d e f_, because the highest grade of light from the window falls at _f_. [Footnote: The diagram Pl. III, No. 1 belongs to this chapter as well as the text given in No. 148. Lines 7-11 (compare lines 8-12 of No. 148) which are written within the diagram, evidently apply to both sections and have therefore been inserted in both.] 276. OF THE COLOURS OF SIMPLE DERIVED SHADOWS. The colour of derived shadows is always affected by that of the body towards which they are cast. To prove this: let an opaque body be placed between the plane _s c t d_ and the blue light _d e_ and the red light _a b_, then I say that _d e_, the blue light, will fall on the whole surface _s c t d_ excepting at _o p_ which is covered by the shadow of the body _q r_, as is shown by the straight lines _d q o e r p_. And the same occurs with the light _a b_ which falls on the whole surface _s c t d_ excepting at the spot obscured by the shadow _q r_; as is shown by the lines _d q o_, and _e r p_. Hence we may conclude that the shadow _n m_ is exposed to the blue light _d e_; but, as the red light _a b_ cannot fall there, _n m_ will appear as a blue shadow on a red background tinted with blue, because on the surface _s c t d_ both lights can fall. But in the shadows only one single light falls; for this reason these shadows are of medium depth, since, if no light whatever mingled with the shadow, it would be of the first degree of darkness &c. But in the shadow at _o p_ the blue light does not fall, because the body _q r_ interposes and intercepts it there. Only the red light _a b_ falls there and tinges the shadow of a red hue and so a ruddy shadow appears on the background of mingled red and blue. The shadow of _q r_ at _o p_ is red, being caused by the blue light _d e_; and the shadow of _q r_ at _o' p'_ is blue being caused by the red light _a b_. Hence we say that the blue light in this instance causes a red derived shadow from the opaque body _q' r'_, while the red light causes the same body to cast a blue derived shadow; but the primary shadow [on the dark side of the body itself] is not of either of those hues, but a mixture of red and blue. The derived shadows will be equal in depth if they are produced by lights of equal strength and at an equal distance; this is proved. [Footnote 53: The text is unfinished in the original.] [Footnote: In the original diagram Leonardo has written within the circle _q r corpo obroso_ (body in shadow); at the spot marked _A, luminoso azzurro_ (blue luminous body); at _B, luminoso rosso_ (red luminous body). At _E_ we read _ombra azzurra_ (blue tinted shadow) and at _D ombra rossa_ (red tinted shadow).] On the nature of colours (277. 278). 277. No white or black is transparent. 278. OF PAINTING. [Footnote 2: See Footnote 3] Since white is not a colour but the neutral recipient of every colour [Footnote 3: _il bianco non e colore ma e inpotentia ricettiva d'ogni colore_ (white is not a colour, but the neutral recipient of every colour). LEON BATT. ALBERTI "_Della pittura_" libro I, asserts on the contrary: "_Il bianco e'l nero non sono veri colori, ma sono alteratione delli altri colori_" (ed. JANITSCHEK, p. 67; Vienna 1877).], when it is seen in the open air and high up, all its shadows are bluish; and this is caused, according to the 4th [prop.], which says: the surface of every opaque body assumes the hue of the surrounding objects. Now this white [body] being deprived of the light of the sun by the interposition of some body between the sun and itself, all that portion of it which is exposed to the sun and atmosphere assumes the colour of the sun and atmosphere; the side on which the sun does not fall remains in shadow and assumes the hue of the atmosphere. And if this white object did not reflect the green of the fields all the way to the horizon nor get the brightness of the horizon itself, it would certainly appear simply of the same hue as the atmosphere. On gradations in the depth of colours (279. 280). 279. Since black, when painted next to white, looks no blacker than when next to black; and white when next to black looks no whiter than white, as is seen by the images transmitted through a small hole or by the edges of any opaque screen ... 280. OF COLOURS. Of several colours, all equally white, that will look whitest which is against the darkest background. And black will look intensest against the whitest background. And red will look most vivid against the yellowest background; and the same is the case with all colours when surrounded by their strongest contrasts. On the reflection of colours (281-283). 281. PERSPECTIVE. Every object devoid of colour in itself is more or less tinged by the colour [of the object] placed opposite. This may be seen by experience, inasmuch as any object which mirrors another assumes the colour of the object mirrored in it. And if the surface thus partially coloured is white the portion which has a red reflection will appear red, or any other colour, whether bright or dark. PERSPECTIVE. Every opaque and colourless body assumes the hue of the colour reflected on it; as happens with a white wall. 282. PERSPECTIVE. That side of an object in light and shade which is towards the light transmits the images of its details more distinctly and immediately to the eye than the side which is in shadow. PERSPECTIVE. The solar rays reflected on a square mirror will be thrown back to distant objects in a circular form. PERSPECTIVE. Any white and opaque surface will be partially coloured by reflections from surrounding objects. [Footnote 281. 282: The title line of these chapters is in the original simply _"pro"_, which may be an abbreviation for either _Propositione_ or _Prospettiva_--taking Prospettiva of course in its widest sense, as we often find it used in Leonardo's writings. The title _"pro"_ has here been understood to mean _Prospettiva_, in accordance with the suggestion afforded by page 10b of this same MS., where the first section is headed _Prospettiva_ in full (see No. 94), while the four following sections are headed merely _"pro"_ (see No. 85).] 283. WHAT PORTION OF A COLOURED SURFACE OUGHT IN REASON TO BE THE MOST INTENSE. If _a_ is the light, and _b_ illuminated by it in a direct line, _c_, on which the light cannot fall, is lighted only by reflection from _b_ which, let us say, is red. Hence the light reflected from it, will be affected by the hue of the surface causing it and will tinge the surface _c_ with red. And if _c_ is also red you will see it much more intense than _b_; and if it were yellow you would see there a colour between yellow and red. On the use of dark and light colours in painting (284--286). 284. WHY BEAUTIFUL COLOURS MUST BE IN THE [HIGHEST] LIGHT. Since we see that the quality of colour is known [only] by means of light, it is to be supposed that where there is most light the true character of a colour in light will be best seen; and where there is most shadow the colour will be affected by the tone of that. Hence, O Painter! remember to show the true quality of colours in bright lights. 285. An object represented in white and black will display stronger relief than in any other way; hence I would remind you O Painter! to dress your figures in the lightest colours you can, since, if you put them in dark colours, they will be in too slight relief and inconspicuous from a distance. And the reason is that the shadows of all objects are dark. And if you make a dress dark there is little variety in the lights and shadows, while in light colours there are many grades. 286. OF PAINTING. Colours seen in shadow will display more or less of their natural brilliancy in proportion as they are in fainter or deeper shadow. But if these same colours are situated in a well-lighted place, they will appear brighter in proportion as the light is more brilliant. THE ADVERSARY. The variety of colours in shadow must be as great as that of the colours in the objects in that shadow. THE ANSWER. Colours seen in shadow will display less variety in proportion as the shadows in which they lie are deeper. And evidence of this is to be had by looking from an open space into the doorways of dark and shadowy churches, where the pictures which are painted in various colours all look of uniform darkness. Hence at a considerable distance all the shadows of different colours will appear of the same darkness. It is the light side of an object in light and shade which shows the true colour. On the colours of the rainbow (287. 288). 287. Treat of the rainbow in the last book on Painting, but first write the book on colours produced by the mixture of other colours, so as to be able to prove by those painters' colours how the colours of the rainbow are produced. 288. WHETHER THE COLOURS OF THE RAINBOW ARE PRODUCED BY THE SUN. The colours of the rainbow are not produced by the sun, for they occur in many ways without the sunshine; as may be seen by holding a glass of water up to the eye; when, in the glass--where there are those minute bubbles always seen in coarse glass--each bubble, even though the sun does not fall on it, will produce on one side all the colours of the rainbow; as you may see by placing the glass between the day light and your eye in such a way as that it is close to the eye, while on one side the glass admits the [diffused] light of the atmosphere, and on the other side the shadow of the wall on one side of the window; either left or right, it matters not which. Then, by turning the glass round you will see these colours all round the bubbles in the glass &c. And the rest shall be said in its place. THAT THE EYE HAS NO PART IN PRODUCING THE COLOURS OF THE RAINBOW. In the experiment just described, the eye would seem to have some share in the colours of the rainbow, since these bubbles in the glass do not display the colours except through the medium of the eye. But, if you place the glass full of water on the window sill, in such a position as that the outer side is exposed to the sun's rays, you will see the same colours produced in the spot of light thrown through the glass and upon the floor, in a dark place, below the window; and as the eye is not here concerned in it, we may evidently, and with certainty pronounce that the eye has no share in producing them. OF THE COLOURS IN THE FEATHERS OF CERTAIN BIRDS. There are many birds in various regions of the world on whose feathers we see the most splendid colours produced as they move, as we see in our own country in the feathers of peacocks or on the necks of ducks or pigeons, &c. Again, on the surface of antique glass found underground and on the roots of turnips kept for some time at the bottom of wells or other stagnant waters [we see] that each root displays colours similar to those of the real rainbow. They may also be seen when oil has been placed on the top of water and in the solar rays reflected from the surface of a diamond or beryl; again, through the angular facet of a beryl every dark object against a background of the atmosphere or any thing else equally pale-coloured is surrounded by these rainbow colours between the atmosphere and the dark body; and in many other circumstances which I will not mention, as these suffice for my purpose. _VI._ _'Prospettiva de' colri' (Perspective of Colour)_ _and_ _'Prospettiva aerea' (Aerial Perspective)._ _Leonardo distinctly separates these branches of his subject, as may be seen in the beginning of No._ 295. _Attempts have been made to cast doubts on the results which Leonardo arrived at by experiment on the perspective of colour, but not with justice, as may be seen from the original text of section_ 294. _The question as to the composition of the atmosphere, which is inseparable from a discussion on Aerial Perspective, forms a separate theory which is treated at considerable length. Indeed the author enters into it so fully that we cannot escape the conviction that he must have dwelt with particular pleasure on this part of his subject, and that he attached great importance to giving it a character of general applicability._ General rules (289--291). 289. The variety of colour in objects cannot be discerned at a great distance, excepting in those parts which are directly lighted up by the solar rays. 290. As to the colours of objects: at long distances no difference is perceptible in the parts in shadow. 291. OF THE VISIBILITY OF COLOURS. Which colour strikes most? An object at a distance is most conspicuous, when it is lightest, and the darkest is least visible. An exceptional case. 292. Of the edges [outlines] of shadows. Some have misty and ill defined edges, others distinct ones. No opaque body can be devoid of light and shade, except it is in a mist, on ground covered with snow, or when snow is falling on the open country which has no light on it and is surrounded with darkness. And this occurs [only] in spherical bodies, because in other bodies which have limbs and parts, those sides of limbs which face each other reflect on each other the accidental [hue and tone] of their surface. An experiment. 293. ALL COLOURS ARE AT A DISTANCE UNDISTINGUISHABLE AND UNDISCERNIBLE. All colours at a distance are undistinguishable in shadow, because an object which is not in the highest light is incapable of transmitting its image to the eye through an atmosphere more luminous than itself; since the lesser brightness must be absorbed by the greater. For instance: We, in a house, can see that all the colours on the surface of the walls are clearly and instantly visible when the windows of the house are open; but if we were to go out of the house and look in at the windows from a little distance to see the paintings on those walls, instead of the paintings we should see an uniform deep and colourless shadow. The practice of the prospettiva de colori. 294. HOW A PAINTER SHOULD CARRY OUT THE PERSPECTIVE OF COLOUR IN PRACTICE. In order to put into practice this perspective of the variation and loss or diminution of the essential character of colours, observe at every hundred braccia some objects standing in the landscape, such as trees, houses, men and particular places. Then in front of the first tree have a very steady plate of glass and keep your eye very steady, and then, on this plate of glass, draw a tree, tracing it over the form of that tree. Then move it on one side so far as that the real tree is close by the side of the tree you have drawn; then colour your drawing in such a way as that in colour and form the two may be alike, and that both, if you close one eye, seem to be painted on the glass and at the same distance. Then, by the same method, represent a second tree, and a third, with a distance of a hundred braccia between each. And these will serve as a standard and guide whenever you work on your own pictures, wherever they may apply, and will enable you to give due distance in those works. [14] But I have found that as a rule the second is 4/5 of the first when it is 20 braccia beyond it. [Footnote: This chapter is one of those copied in the Manuscript of the Vatican library Urbinas 1270, and the original text is rendered here with no other alterations, but in the orthography. H. LUDWIG, in his edition of this copy translates lines 14 and 15 thus: "_Ich finde aber als Regel, dass der zweite um vier Funftel des ersten abnimmt, wenn er namlich zwanzig Ellen vom ersten entfernt ist (?)"_. He adds in his commentary: "_Das Ende der Nummer ist wohl jedenfalls verstummelt_". However the translation given above shows that it admits of a different rendering.] The rules of aerial perspective (295--297). 295. OF AERIAL PERSPECTIVE. There is another kind of perspective which I call Aerial Perspective, because by the atmosphere we are able to distinguish the variations in distance of different buildings, which appear placed on a single line; as, for instance, when we see several buildings beyond a wall, all of which, as they appear above the top of the wall, look of the same size, while you wish to represent them in a picture as more remote one than another and to give the effect of a somewhat dense atmosphere. You know that in an atmosphere of equal density the remotest objects seen through it, as mountains, in consequence of the great quantity of atmosphere between your eye and them--appear blue and almost of the same hue as the atmosphere itself [Footnote 10: _quado il sole e per leuante_ (when the sun is in the East). Apparently the author refers here to morning light in general. H. LUDWIG however translates this passage from the Vatican copy "_wenn namlich die Sonne (dahinter) im Osten steht_".] when the sun is in the East [Footnote 11: See Footnote 10]. Hence you must make the nearest building above the wall of its real colour, but the more distant ones make less defined and bluer. Those you wish should look farthest away you must make proportionately bluer; thus, if one is to be five times as distant, make it five times bluer. And by this rule the buildings which above a [given] line appear of the same size, will plainly be distinguished as to which are the more remote and which larger than the others. 296. The medium lying between the eye and the object seen, tinges that object with its colour, as the blueness of the atmosphere makes the distant mountains appear blue and red glass makes objects seen beyond it, look red. The light shed round them by the stars is obscured by the darkness of the night which lies between the eye and the radiant light of the stars. 297. Take care that the perspective of colour does not disagree with the size of your objects, hat is to say: that the colours diminish from their natural [vividness] in proportion as the objects at various distances dimmish from their natural size. On the relative density of the atmosphere (298--290). 298. WHY THE ATMOSPHERE MUST BE REPRESENTED AS PALER TOWARDS THE LOWER PORTION. Because the atmosphere is dense near the earth, and the higher it is the rarer it becomes. When the sun is in the East if you look towards the West and a little way to the South and North, you will see that this dense atmosphere receives more light from the sun than the rarer; because the rays meet with greater resistance. And if the sky, as you see it, ends on a low plain, that lowest portion of the sky will be seen through a denser and whiter atmosphere, which will weaken its true colour as seen through that medium, and there the sky will look whiter than it is above you, where the line of sight travels through a smaller space of air charged with heavy vapour. And if you turn to the East, the atmosphere will appear darker as you look lower down because the luminous rays pass less freely through the lower atmosphere. 299. OF THE MODE OF TREATING REMOTE OBJECTS IN PAINTING. It is easy to perceive that the atmosphere which lies closest to the level ground is denser than the rest, and that where it is higher up, it is rarer and more transparent. The lower portions of large and lofty objects which are at a distance are not much seen, because you see them along a line which passes through a denser and thicker section of the atmosphere. The summits of such heights are seen along a line which, though it starts from your eye in a dense atmosphere, still, as it ends at the top of those lofty objects, ceases in a much rarer atmosphere than exists at their base; for this reason the farther this line extends from your eye, from point to point the atmosphere becomes more and more rare. Hence, O Painter! when you represent mountains, see that from hill to hill the bases are paler than the summits, and in proportion as they recede beyond each other make the bases paler than the summits; while, the higher they are the more you must show of their true form and colour. On the colour of the atmosphere (300-307). 300. OF THE COLOUR OF THE ATMOSPHERE. I say that the blueness we see in the atmosphere is not intrinsic colour, but is caused by warm vapour evaporated in minute and insensible atoms on which the solar rays fall, rendering them luminous against the infinite darkness of the fiery sphere which lies beyond and includes it. And this may be seen, as I saw it by any one going up [Footnote 5: With regard to the place spoken of as _M'oboso_ (compare No. 301 line 20) its identity will be discussed under Leonardo's Topographical notes in Vol. II.] Monboso, a peak of the Alps which divide France from Italy. The base of this mountain gives birth to the four rivers which flow in four different directions through the whole of Europe. And no mountain has its base at so great a height as this, which lifts itself almost above the clouds; and snow seldom falls there, but only hail in the summer, when the clouds are highest. And this hail lies [unmelted] there, so that if it were not for the absorption of the rising and falling clouds, which does not happen twice in an age, an enormous mass of ice would be piled up there by the hail, and in the middle of July I found it very considerable. There I saw above me the dark sky, and the sun as it fell on the mountain was far brighter here than in the plains below, because a smaller extent of atmosphere lay between the summit of the mountain and the sun. Again as an illustration of the colour of the atmosphere I will mention the smoke of old and dry wood, which, as it comes out of a chimney, appears to turn very blue, when seen between the eye and the dark distance. But as it rises, and comes between the eye and the bright atmosphere, it at once shows of an ashy grey colour; and this happens because it no longer has darkness beyond it, but this bright and luminous space. If the smoke is from young, green wood, it will not appear blue, because, not being transparent and being full of superabundant moisture, it has the effect of condensed clouds which take distinct lights and shadows like a solid body. The same occurs with the atmosphere, which, when overcharged with moisture appears white, and the small amount of heated moisture makes it dark, of a dark blue colour; and this will suffice us so far as concerns the colour of the atmosphere; though it might be added that, if this transparent blue were the natural colour of the atmosphere, it would follow that wherever a larger mass air intervened between the eye and the element of fire, the azure colour would be more intense; as we see in blue glass and in sapphires, which are darker in proportion as they are larger. But the atmosphere in such circumstances behaves in an opposite manner, inasmuch as where a greater quantity of it lies between the eye and the sphere of fire, it is seen much whiter. This occurs towards the horizon. And the less the extent of atmosphere between the eye and the sphere of fire, the deeper is the blue colour, as may be seen even on low plains. Hence it follows, as I say, that the atmosphere assumes this azure hue by reason of the particles of moisture which catch the rays of the sun. Again, we may note the difference in particles of dust, or particles of smoke, in the sun beams admitted through holes into a dark chamber, when the former will look ash grey and the thin smoke will appear of a most beautiful blue; and it may be seen again in in the dark shadows of distant mountains when the air between the eye and those shadows will look very blue, though the brightest parts of those mountains will not differ much from their true colour. But if any one wishes for a final proof let him paint a board with various colours, among them an intense black; and over all let him lay a very thin and transparent [coating of] white. He will then see that this transparent white will nowhere show a more beautiful blue than over the black--but it must be very thin and finely ground. [Footnote 7: _reta_ here has the sense of _malanno_.] 301. Experience shows us that the air must have darkness beyond it and yet it appears blue. If you produce a small quantity of smoke from dry wood and the rays of the sun fall on this smoke, and if you then place behind the smoke a piece of black velvet on which the sun does not shine, you will see that all the smoke which is between the eye and the black stuff will appear of a beautiful blue colour. And if instead of the velvet you place a white cloth smoke, that is too thick smoke, hinders, and too thin smoke does not produce, the perfection of this blue colour. Hence a moderate amount of smoke produces the finest blue. Water violently ejected in a fine spray and in a dark chamber where the sun beams are admitted produces these blue rays and the more vividly if it is distilled water, and thin smoke looks blue. This I mention in order to show that the blueness of the atmosphere is caused by the darkness beyond it, and these instances are given for those who cannot confirm my experience on Monboso. 302. When the smoke from dry wood is seen between the eye of the spectator and some dark space [or object], it will look blue. Thus the sky looks blue by reason of the darkness beyond it. And if you look towards the horizon of the sky, you will see the atmosphere is not blue, and this is caused by its density. And thus at each degree, as you raise your eyes above the horizon up to the sky over your head, you will see the atmosphere look darker [blue] and this is because a smaller density of air lies between your eye and the [outer] darkness. And if you go to the top of a high mountain the sky will look proportionately darker above you as the atmosphere becomes rarer between you and the [outer] darkness; and this will be more visible at each degree of increasing height till at last we should find darkness. That smoke will look bluest which rises from the driest wood and which is nearest to the fire and is seen against the darkest background, and with the sunlight upon it. 303. A dark object will appear bluest in proportion as it has a greater mass of luminous atmosphere between it and the eye. As may be seen in the colour of the sky. 304. The atmosphere is blue by reason of the darkness above it because black and white make blue. 305. In the morning the mist is denser above than below, because the sun draws it upwards; hence tall buildings, even if the summit is at the same distance as the base have the summit invisible. Therefore, also, the sky looks darkest [in colour] overhead, and towards the horizon it is not blue but rather between smoke and dust colour. The atmosphere, when full of mist, is quite devoid of blueness, and only appears of the colour of clouds, which shine white when the weather is fine. And the more you turn to the west the darker it will be, and the brighter as you look to the east. And the verdure of the fields is bluish in a thin mist, but grows grey in a dense one. The buildings in the west will only show their illuminated side, where the sun shines, and the mist hides the rest. When the sun rises and chases away the haze, the hills on the side where it lifts begin to grow clearer, and look blue, and seem to smoke with the vanishing mists; and the buildings reveal their lights and shadows; through the thinner vapour they show only their lights and through the thicker air nothing at all. This is when the movement of the mist makes it part horizontally, and then the edges of the mist will be indistinct against the blue of the sky, and towards the earth it will look almost like dust blown up. In proportion as the atmosphere is dense the buildings of a city and the trees in a landscape will look fewer, because only the tallest and largest will be seen. Darkness affects every thing with its hue, and the more an object differs from darkness, the more we see its real and natural colour. The mountains will look few, because only those will be seen which are farthest apart; since, at such a distance, the density increases to such a degree that it causes a brightness by which the darkness of the hills becomes divided and vanishes indeed towards the top. There is less [mist] between lower and nearer hills and yet little is to be distinguished, and least towards the bottom. 306. The surface of an object partakes of the colour of the light which illuminates it; and of the colour of the atmosphere which lies between the eye and that object, that is of the colour of the transparent medium lying between the object and the eye; and among colours of a similar character the second will be of the same tone as the first, and this is caused by the increased thickness of the colour of the medium lying between the object and the eye.