Noble, Thomas; Clark, John Heaviside [Ill.]: Practical Perspective, Exemplified On Landscapes (London, 1809)

14

PRACTICAL PERSPECTIVE;

OBSERVATIONS.

SeC. 2. I. It is apparent to every one that distance lessens the appearance of every/
object, and that every object is lost, in the boundary of our sight, which is the horizon, and!
is here represented by the horizontal line.

H. As we can only direct our sight to one point at a time, so there can be only
one point of sight in a picture.

III. All walls, sides of buildings, roads, &c. and, in short, all lines, that are directed
straight forward from the spectator, must tend to the point of sight.

IV. All walls, sides of buildings, roads, &c. that are oblique to the spectator, that is,,
are not directly straight forwards, tend to some point in the horizontal line, but not
to the point of sight.

V. All sloping walls, roofs of houses, hills, &c. must tend to some point either above'
or below the horizontal line.

VI. In explaining the following plates, these points will be called vanishing points

VII. By looking at the first explanatory plate, the meaning of a cone or body of rays,,
cut by the plane of the picture (a thing particularly dwelt upon by all writers on
perspective) will be easily conceived.

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The eye of the spectator is the point or apex of the cone, and the rays (represented
on the plate by fine dotted lines) proceed to every point of the original objects.

VIII. These rays may be supposed to pierce through the plane of the picture, or
to be cut by it: each ray must necessarily, in either case, touch the surface of the
picture in a point. These points together make up the perspective representation of the
objects; and it is the business of perspective to find the positions of these points on

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the plane of the picture.