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)

21

LETTER III.

In the present letter, it is not intended to enter into the geometrical problems by
which all that is advanced on the art of Perspective could be proved, but profiting
by the exertions of those mathematicians who have clearly demonstrated the truth of the
various propositions, we shall endeavour to render their labours practically useful.
Yet there are certain terms and definitions of points, lines, and figures, with the mean-
ing of which it is absolutely necessary to be acquainted, before we can apply
them, or understand the terms used by writers, either on drawing or any other
scientific subject.
We shall begin with figures. This term is net confined to the Arabic numerals
which are used in arithmetic, but is in this case applied to circles, squares, parallelo-
grams, right angles, equilateral triangles, &c.; and we will now describe how' several
of those used in geometry or perspective are formed.