perspective as this, is to go and draw it from
nature, and even then to use our judgement, as he did, as to how much we
may emphasize or even exaggerate certain features.

[Illustration: Fig. 95. Turner's View from Richmond Hill.]

Note in this view the foreground on which the principal figures stand is
on a level with the perspective plane, while the river and surrounding
park and woods are hundreds of feet below us and stretch away for miles
into the distance. The contrasts obtained by this arrangement increase
the illusion of space, and the figures in the foreground give as it were
a standard of measurement, and by their contrast to the size of the
trees show us how far away those trees are.

XL

HOW TO ASCERTAIN THE RELATIVE HEIGHTS OF FIGURES ON AN INCLINED PLANE

[Illustration: Fig. 96.]

The three figures to the right marked _f_, _g_, _b_ (Fig. 96) are on
level ground, and we measure them by the vanishing scale _aS_, _bS_.
Those to the left, which are repetitions of them, are on an inclined
plane, the vanishing point of which is _S'_; by the side of this plane
we have placed another vanishing scale _a'S'_, _b'S'_, by which we
measure the figures on that incline in the same way as on the level
plane. It will be seen that if a horizontal line is drawn from the foot
of one of these figures, say _G_, to point _O_ on the edge of the
incline, then dropped vertically to _o'_, then again carried on to _o''_
where the other figure _g_ is, we find it is the same height and also
that the other vanishing scale is the same width at that distance, so
that we can work from either one or the other. In the event of the
rising ground being uneven we can make use of the scale on the level
plane.

XLI

HOW TO FIND THE DISTANCE OF A GIVEN FIGURE OR POINT FROM THE BASE LINE

[Illustration: Fig. 97.]

Let _P_ be the given figure. Form scale _ACS_, _S_ being the point of
sight and _D_ the distance. Draw horizontal _do_ through _P_. From _A_
draw diagonal _AD_ to distance point, cutting _do_ in _o_, through _o_
draw _SB_ to base, and we now have a square _AdoB_ on the perspective
plane; and as figure _P_ is standing on the far side of that square it
must be the distance _AB_, which is one side of it, from the base
line--or picture plane. For figures very far away it might be necessary
to make use of half-distance.

XLII

HOW TO MEASURE THE HEIGHT OF FIGURES ON UNEVEN GROUND

In previous prob