Whittock, Nathaniel: The Oxford Drawing Book, Or The Art Of Drawing, And The Theory And Practice Of Perspective: In A Series Of Letters Containing Progressive Information On Sketching, Drawing, And Colouring Landscape Scenery, Animals, And The Human Figure: With A New Method Of Practical Perspective: Detailed In A Novel, Easy, And Perspicuous Style, For The Use Of Teachers, Or For Self-Instruction. Embellished With Upwards Of One Hundred And Fifty Lithographic Drawings, From Real Views, Taken Expressly For This Work (Oxford , London, 1825)

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No. 1. is a small square viewed directly from the front, put in perspective, cd,
shews one side of the square, and if we draw lines from c and d to the point of sight,
they will give the sides c a, and d b ; but we cannot obtain the remaining side without
having recourse to the points of distance, which are here placed on the horizon, at
equal distance from the point of sight. A line drawn from c or d to the point of dis-
tance, will intersect the lines drawn to the point of sight, and another line drawn
from the points of intersection, parallel to the base line, will complete the square :
this rule will answer for any square figure viewed from the front.
No. 2. shews the side or oblique view of the same object. In this position, it pre-
sents two sides to the view; and the point of sight, instead of appearing in the middle
of the horizon, as was the case in the front view, must be placed nearer the side of
the picture. The real point of sight, you must recollect, is still in the centre of the
horizontal line, but the position of the eye being greatly on one side of the object, the
horizon is so much extended, that the whole of it cannot be given on the paper, and for
the same reason, only one point of distance can be introduced. This figure is not
lettered, because the process of putting this square in perspective, is the same as in
the preceding example.