Cox, David: A series of progressive lessons intended to elucidate the art of painting: with introductory illustrations on perspective and drawing with pencil (London, 1845)

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simplify the adaptation of the essential rules of Perspective required in
Sketching from Nature.
Whatever be the scene proposed to be delineated, (See Fig. 1.) it is proper,
first, to determine the base line., A A, of the drawing; upon which line the
perpendicular sides, B B, are to be raised. Then the horizontal line C must
be drawn parallel to the base line, which determines the height of the eye of
the spectator. There can be no precise rule for the situation of this line. If
it be placed high, the scene will represent what is denominated a bird s-eye
view, or map-like delineation. If the horizontal line be placed low, the view
will appear to have been taken with the eye too near to the ground, and be-
come uninteresting. Too much sky, or too much ground, are equally offensive ;
the horizontal line must therefore depend upon the nature of the subject, and
the taste of the delineator. The point of sight, D, is next to be placed upon
the horizontal line, and its situation is in front of the spectator. Lines
terminating in this point are denominated visual rays, EE; to it all lines of
objects seen obliquely tend, as the view down a long avenue of trees appears
to end in a point. Lines drawn from the base to points of distance, F F, are