Form scale bS, cS; mark off distances 20 feet, 40 feet, &c. Suppose figure K to be 60 feet off. From point at his feet draw horizontal to meet vertical On, which is 60 feet distant. At the point m where this line meets the vertical, measure height mn equal to width of scale at that distance, transfer this to K, and you have the required height of the figure in black.
For the figures under the cliff 20 feet below the perspective plane, form scale FS, GS, making it the same width as the other, namely 5 feet, and proceed in the usual way to find the height of the figures on the sands, which are here supposed to be nearly on a level with the sea, of course making allowance for different heights and various other things.
[ XLIII]
Further Illustration of the Size of Figures at Different Distances and on Uneven Ground
Let ab be the height of a figure, say 6 feet. First form scale aS, bS, the lower line of which, aS, is on a level with the base or on the perspective plane. The figure marked C is close to base, the group of three is farther off (24 feet), and 6 feet higher up, so we measure the height on the vanishing scale and also above it. The two girls carrying fish are still farther off, and about 12 feet below. To tell how far a figure is away, refer its measurements to the vanishing scale (see [Fig. 96]).
Fig. 99.