Robson, William: Grammigraphia; or the Grammar of Drawing. (London, 1799)

8i
SECTION IV.

Rules governing the Seven Situations.

1. ,

2.—Parallel trntf) tlje peusoecttoe Plane*

RULE.—The Parallels of this Situation remain always re-
spectively Parallel, and do not converge in any
point. ________

4. parallel totto tlje Statical plane, ano lotto toe 0rouno Plane,

IN ALL ITS FIVE VARIATIONS.

RULE.—They vaniih in the point of sight.

5. Oblique ta toe Vertical plane, out parallel iottt} tlje ®touno

Plane,

IN ITS FOUR VARIATIONS.

RULE.—They vanish in the intersecting point of their
own Obliquity, on the Horizontal Line.

EXPLANATION.

fbe Obliquity of this Situation, being produced, in any degree
of Obliquity, to the Horizontal Line, all its Parallels will
converge in the same point of intersection.

6. ©bltque to toe ©rotmo plane, out parallel uritlj toe Vertical

Plane,

IN ITS TWO VARIATIONS.

RULE.—They vanish in the Perpendicular, at the point
of their intersection, either above or below the
Horizontal.

7. ©faltque to tlje <55rouno plane, ano ©bltque to toe Vertical

Plane.

RULE.—They vanish agreeably to the intersection of their
own Obliquity, above or below the Horizontal
Plane.