Note Return to text — THE ELEMENTS OF PERSPECTIVE.

Evidently, the farther from the point T we place the glass, making S T longer, the larger will be the image; and the nearer we place it to T, the smaller the image, and that in a fixed ratio. Let the distance D T be the direct distance from the Station-point to the foot of the object. Then, if we place the glass A B at one-third of that whole distance, P′ Q′ will be one-third of the real height of the object; if we place the glass at two-thirds of the distance, as at E F, P″ Q″ (the height of the image at that point) will be two-thirds the height[Footnote 5] of the object, and so on. Therefore the mathematical law is that P′ Q′ will be to P Q as S T to D T. I put this ratio clearly by itself that you may remember it: