It is easy to understand that if 2 objects equal to each other are placed side by side the one at 3 braccia distance looks smaller than that placed at 2 braccia. This however is rather theoretical than for practice, because you stand close by [Footnote 11: Instead of '_se preso_' (=_sie presso_) M. RAVAISSON reads '_sempre se_' which gives rise to the unmeaning rendering: '_parceque toujours_ ...'].
All the objects in the foreground, whether large or small, are to be drawn of their proper size, and if you see them from a distance they will appear just as they ought, and if you see them close they will diminish of themselves.
[Footnote 15: Compare No. 526 line 18.] Take care that the vertical plan on which you work out the perspective of the objects seen is of the same form as the wall on which the work is to be executed.
The size of the figures represented ought to show you the distance they are seen from. If you see a figure as large as nature you know it appears to be close to the eye.
WHERE A SPECTATOR SHOULD STAND TO LOOK AT A PICTURE.
Supposing _a b_ to be the picture and _d_ to be the light, I say that if you place yourself between _c_ and _e_ you will not understand the picture well and particularly if it is done in oils, or still more if it is varnished, because it will be lustrous and somewhat of the nature of a mirror. And for this reason the nearer you go towards the point _c_, the less you will see, because the rays of light falling from the window on the picture are reflected to that point. But if you place yourself between _e_ and _d_ you will get a good view of it, and the more so as you approach the point _d_, because that spot is least exposed to these reflected rays of light.
THE PRACTICAL METHODS OF LIGHT AND SHADE AND AERIAL PERSPECTIVE.
OF PAINTING: OF THE DARKNESS OF THE SHADOWS, OR I MAY SAY, THE BRIGHTNESS OF THE LIGHTS.
Although practical painters attribute to all shaded objects--trees, fields, hair, beards and skin--four degrees of darkness in each colour they use: that is to say first a dark foundation, secondly a spot of colour somewhat resembling the form of the details, thirdly a somewhat brighter and more defined portion, fourthly the lights which are more conspicuous than other parts of the figure; still to me it appears that these gradations are infinite upon a continuous surface which is in itself infinitely divisible, and I prove it thus:--[Footnote 7: See Pl. XXXI, No. 1; the two upper sketches.] Let _a g_ be a continuous surface and let _d_ be the light which illuminates it; I say--by the 4th [proposition] which says that that side of an illuminated body is most highly lighted which is nearest to the source of light--that therefore _g_ must be darker than _c_ in proportion as the line _d g_ is longer than the line _d c_, and consequently that these gradations of light--or rather of shadow, are not 4 only, but may be conceived of as infinite, because _c d_ is a continuous surface and every continuous surface is infinitely divisible; hence the varieties in the length of lines extending between the light and the illuminated object are infinite, and the proportion of the light will be the same as that of the length of the lines between them; extending from the centre of the luminous body to the surface of the illuminated object.