Gravesande, Willem Jacob 's - An essay on perspective

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11555on PERSPECTIVE. making theſe Abbreviations, will be laid down
in the following Methods.

Method II.
70. By the accidental Point of inclin’d Lines.

Thro’ F, the accidental Point of the inclin’d
11Fig. 36. parallel Lines, draw F H, parallel to the Baſe
Line, and equal to F G. And let A be the
Point, wherein one of the inclin’d Lines meets
the Geometrical Plane.

Operation.

Aſſume R Q in the Baſe Line, equal to the
inclin’d Line; and draw Lines from the Points
R and Q, to the Point Z, taken at pleaſure in
the Horizontal Plane.

Thro’ a, the Perſpective of A, draw a N pa-
rallel to the Baſe Line; in which aſſume a L,
equal to M N; and draw a Line from the Point
a, to the Point F; and from the Point L, draw
another to the Point H. Then a T will be the
Perſpective ſought.

Demonstration.

By the Nature of the accidental Point, 2214. Perſpective ſought is a Part of the Line a F;
and therefore, we are only to demonſtrate,
that the Extremity of the faid Perpendicular is in
the Line L H. Which may be thus done.

Let us ſuppoſe a Line, A I, to paſs thro’ the
Point A, parallel to the Baſe Line, and equal to
the inclin’d Line. It is then manifeſt , 3356. L is the Perſpective of I; and conſequently,
L H is the Appearance of a Line 44@@

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Scan	Original
111
112
113	53
114	54
115	55
116	56
117
118
119
120	57
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

Scan	Original
111
112
113	53
114	54
115	55
116	56
117
118
119
120	57
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

Scan	Original
111
112
113	53
114	54
115	55
116	56
117
118
119
120	57
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