Gravesande, Willem Jacob 's - An essay on perspective

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12660An ESSAY tal Plane, or one of the Points of Diſtance on the
Horizontal Line.

The Repreſentation of two Points of theſe
Figures muſt be firſt found ; and then by 1124. of theſe two Points the Appearances of others
may be had .

2238.

Example.

Let A B C D E, be a Pentagon, whoſe Ap-
33Fig. 40. pearance is requir’d; V the Point of Sight; and
V F the ſixth Part of the Eye’s Diſtance from
the perſpective Plane. Now find b and e 4424. Appearance of B and E, by means of which,
the Appearance of the Point A will be had . 5538. In like Manner, by means of the Repreſenta-
tion of A and E, will that of D be had; and
by uſing B and A, the Perſpective of C may be
found.

76. Note, the Perſpective of Lines perpendicu-
lar to the Geometrical Plane ; as alſo of 6655. inclined thereto , may be found by the 7769. of the precedent Chapter.

Problem II.

77. To throw Figures, which are in the Geometri-
cal Plane into Perſpective, when the Eye is ſo oblique
that it cannot be marked in the Horizontal Plane,
or the Point of Sight in the Horizontal Line.

We muſt proceed here according to the Di-
rections of the precedent Problem, after having
found the Perſpective of ſeveral Points of the
given Figures.

At any Point C, taken at Pleaſure in the Baſe
Line, draw the Perpendicular C D to the ſaid
88Fig. 41. Line, and likewiſe draw the Line C E from the
ſame Point in ſuch manner, that if it could

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Scan	Original
121	58
122
123
124
125	59
126	60
127
128
129
130	61
131	62
132	63
133	64
134
135
136
137	65
138	66
139	67
140	68
141
142
143
144	69
145	70
146	71
147	72
148
149
150

Scan	Original
121	58
122
123
124
125	59
126	60
127
128
129
130	61
131	62
132	63
133	64
134
135
136
137	65
138	66
139	67
140	68
141
142
143
144	69
145	70
146	71
147	72
148
149
150

Scan	Original
121	58
122
123
124
125	59
126	60
127
128
129
130	61
131	62
132	63
133	64
134
135
136
137	65
138	66
139	67
140	68
141
142
143
144	69
145	70
146	71
147	72
148
149
150