If a house be painted on the pannel B C, at the apparent distance of one mile, and by the side of it a real one be perceived at the true distance of one mile also; which objects are so disposed, that the pannel, or picture, A C, intersects the pyramidical rays with the same opening of angles; yet these two objects will never appear of the same size, nor at the same distance, if seen with both eyes[91].
Chap. CCCXLV.—How to draw a Figure standing upon its Feet, to appear forty Braccia [92] high, in a Space of twenty Braccia, with proportionate Members.
In this, as in any other case, the painter is not to mind what kind of surface he has to work upon; particularly if his painting is to be seen from a determined point, such as a window, or any other opening. Because the eye is not to attend to the evenness or roughness of the wall, but only to what is to be represented as beyond that wall; such as a landscape, or any thing else. Nevertheless a curved surface, such as F R G, would be the best, because it has no angles.
Chap. CCCXLVI.—How to draw a Figure twenty-four Braccia high, upon a Wall twelve Braccia high. Plate XXII.
Draw upon part of the wall M N, half the figure you mean to represent; and the other half upon the cove above, M R. But before that, it will be necessary to draw upon a flat board, or a paper, the profile of the wall and cove, of the same shape and dimension, as that upon which you are to paint. Then draw also the profile of your figure, of whatever size you please, by the side of it; draw all the lines to the point F, and where they intersect the profile M R, you will have the dimensions of your figure as they ought to be drawn upon the real spot. You will find, that on the straight part of the wall M N, it will come of its proper form, because the going off perpendicularly will diminish it naturally; but that part which comes upon the curve will be diminished upon your drawing. The whole must be traced afterwards upon the real spot, which is similar to M N. This is a good and safe method.