Gravesande, Willem Jacob 's - An essay on perspective

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13765on PERSPECTIVE. being produced, will meet each other in the
Horizontal Line.

CHAP. V.

Of throwing Figures into Perſpective, when
the Perſpective Plane is conſider’d as being
inclined.

Problem I.

81. TO find the Perſpective of a Figure in the
11Fig. 44. Geometrical Plane.

Let X be the Vertical Plane; S I the Station
Line, S the Station Point, and H the Interſecti-
on of the Station Line and Baſe Line. Now
draw the Vertical Line H V through the Point H,
making an Angle with S I, equal to the Angle
of Inclination of the perſpective Plane; then
raiſe the Perpendicular I O to S I, in the Sta-
tion Point S, equal to the Height of the Eye;
and through the Extremity of the ſaid Perpen-
dicular, draw the principal Ray O V, paral-
lel to S I, and cutting H V in the Point of
Sight V.

Now it is evident, that O V determines the
Length of the principal Ray, and H V the Di-
ſtance from the Baſe Line to the Horizontal
Line; and ſince the Demonſtration of the
Problems in the aforegoing Chapters regarding
the Geometrical Plane, have alſo Relation to
the perſpective Plane being inclined, the ſaid
Problems may be here uſed; and conſequently,
this inclined perſpective Plane is reduced to a
Perpendicular one, view’d by an Eye, whoſe
Height is H V, and Diſtance O V.

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Scan	Original
31	10
32	11
33	12
34	13
35	14
36	15
37	16
38
39
40
41	17
42	18
43	19
44	20
45
46
47
48	21
49	22
50	23
51	24
52
53
54
55	25
56	26
57
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60	27