Gravesande, Willem Jacob 's - An essay on perspective

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11656An ESSAY through I, and the Extremity of the propoſed
Line; and therefore the Perſpective of this Ex-
tremity is in the Line L H; which was to be
demonſtrated.

Note, if F H had been aſſumed, the one half,
or one third, & c. of what it is; then it is mani-
feſt that R Q muſt alfo have been taken 1119. to the one half, or third Part, & c. of C E.

Method. III.

71. Forinclined Lines not meeting the Geometrical
Plane.

Let A and B be the Seats of the Extremities of
22Fig. 37. the given Line. Let X repreſent a Plane paſſing
through the given Line perpendicular to the
Geometrical Plane. Likewiſe let M N in this
Plane, repreſent the Line whoſe Perſpective is re-
quir’d; and let C N and P M be perpendicular to
the Geometrical Plane: Whence P C repreſents
A B, and conſequently is equal thereto.

Operation.

Find the Point I , the Perſpective of a 3350. above the Point A, the Height of C N; and
draw the Line B S, from the Point B, to the
Station Point I, cutting the Baſe Line in E; and
from the Point I, draw a Line to the accidental
Point F; which cut by a Perpendicular to the
Baſe Line, raiſed at the Point E; and then I T
will be the Appearance ſought.

Method IV.

72. For inclined Lines parallel to the perſpective
Plane.

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Scan	Original
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94	43
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96	45
97	46
98
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103
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105
106	49
107	50
108	51
109	52
110
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113	53
114	54
115	55
116	56
117
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120	57

Scan	Original
91
92
93
94	43
95	44
96	45
97	46
98
99
100
101	47
102	48
103
104
105
106	49
107	50
108	51
109	52
110
111
112
113	53
114	54
115	55
116	56
117
118
119
120	57

Scan	Original
91
92
93
94	43
95	44
96	45
97	46
98
99
100
101	47
102	48
103
104
105
106	49
107	50
108	51
109	52
110
111
112
113	53
114	54
115	55
116	56
117
118
119
120	57