XLV

FURTHER ILLUSTRATION OF THE DESCENDING PLANE

In the centre of this picture (Fig. 102) we suppose the road to be
descending till it reaches a tunnel which goes under a road or leads to
a river (like one leading out of the Strand near Somerset House). It is
drawn on the same principle as the foregoing figure. Of course to see
the road the spectator must get pretty near to it, otherwise it will be
out of sight. Also a level plane must be shown, as by its contrast to
the other we perceive that the latter is going down hill.

XLVI

FURTHER ILLUSTRATION OF UNEVEN GROUND

An extended view drawn from a height of about 30 feet from a road that
descends about 45 feet.

[Illustration: Fig. 103. Farningham.]

In drawing a landscape such as Fig. 103 we have to bear in mind the
height of the horizon, which being exactly opposite the eye, shows us at
once which objects are below and which are above us, and to draw them
accordingly, especially roofs, buildings, walls, hedges, &c.; also it is
well to sketch in the different fields figures of men and cattle, as
from the size of these we can judge of the rest.

XLVII

THE PICTURE STANDING ON THE GROUND

Let _K_ represent a frame placed vertically and at a given distance in
front of us. If stood on the ground our foreground will touch the base
line of the picture, and we can fix up a standard of measurement both on
the base and on the side as in this sketch, taking 6 feet as about the
height of the figures.

[Illustration: Fig. 104. Toledo.]

XLVIII

THE PICTURE ON A HEIGHT

If we are looking at a scene from a height, that is from a terrace, or a
window, or a cliff, then the near foreground, unless it be the terrace,
window-sill, &c., would not come into the picture, and we could not see
the near figures at _A_, and the nearest to come into view would be
those at _B_, so that a view from a window, &c., would be as it were
without a foreground. Note that the figures at _B_ would be (according
to this sketch) 30 feet from the picture plane and about 18 feet below
the base line.

[Illustration: Fig. 105.]

BOOK THIRD

XLIX

ANGULAR PERSPECTIVE

Hitherto we have spoken only of parallel perspective, which is
comparatively easy, and in our first figure we placed the cube with one
of its sides either touching or parallel to the transparent plane. We
now place it so that one angle only (_ab_), touches the picture.

[Illu