Chap. CXXV.—How to give the proper Dimension to Objects in Painting.
In order to give the appearance of the natural size, if the piece be small (as miniatures), the figures on the fore-ground are to be finished with as much precision as those of any large painting, because being small they are to be brought up close to the eye. But large paintings are seen at some distance; whence it happens, that though the figures in each are so different in size, in appearance they will be the same. This proceeds from the eye receiving those objects under the same angle; and it is proved thus. Let the large painting be B C, the
eye A, and D E a pane of glass, through which are seen the figures situated at B C. I say that the eye being fixed, the figures in the copy of the paintings B C are to be smaller, in proportion as the glass D E is nearer the eye A, and are to be as precise and finished. But if you will execute the picture B C upon the glass D E, this ought to be less finished than the picture B C, and more so than the figure M N transferred upon the glass F G; because, supposing the figure P O to be as much finished as the natural one in B C, the perspective of O P would be false, since, though in regard to the diminution of the figure it would be right, B C being diminished in P O, the finishing would not agree with the distance, because in giving it the perfection of the natural B C, B C would appear as near as O P; but, if you search for the diminution of O P, O P will be found at the distance B C, and the diminution of the finishing as at F G.