Gravesande, Willem Jacob 's - An essay on perspective

Scan	Original
71	32
72	33
73	34
74	35
75	36
76
77
78
79
80
81
82
83
84
85	37
86	38
87	39
88	40
89	41
90	42
91
92
93
94	43
95	44
96	45
97	46
98
99
100

11454An ESSAY

Operation.

In ſome ſeparate Place, draw the Lines C E
and C P, making an Angle with each other
equal to the Angle of Inclination of the given
Line; and in one of theſe Lines, aſſume C E
equal to the given Line, and let fall the Perpen-
dicular E P, from the Point E upon the other
Line. Then aſſume A B, in the Direction of
the propos’d Line, equal to C P; and after ha-
ving found a, the Perſpective of A, and the
Point T , the Perſpective of a Point 1150. above B, the Height of P E; join the Points a
and T by a right Line; and the ſought Appear-
ance will be had.

Demonstration.

If from the Extremity of the inclin’d Line, a
Perpendicular be let fall upon the Geometrical
Plane, the ſaid Perpendicular will meet this
Plane in the Point B, and will be equal to P E;
as is evident by the Conſtruction of the Figure
C P E. But the Point T is the Repreſentation
of the Extremity of this Perpendicular; and
therefore it is alſo the Extremity of the inclin’d
Line. Which was to be demonſtrated.

Remarks.

There are ſome Caſes of this Propoſition, that
may be ſhorten’d. As, 1. When there are ſeve-
ral Lines of this Kind parallel between them-
ſelves, and whoſe accidental Point can be
found : And, 2. When an inclin’d Line is 2268. rallel to the perſpective Plane. The Manner

Page concordance

Text layer

Text normalization

Search

Scan	Original
71	32
72	33
73	34
74	35
75	36
76
77
78
79
80
81
82
83
84
85	37
86	38
87	39
88	40
89	41
90	42
91
92
93
94	43
95	44
96	45
97	46
98
99
100

Scan	Original
71	32
72	33
73	34
74	35
75	36
76
77
78
79
80
81
82
83
84
85	37
86	38
87	39
88	40
89	41
90	42
91
92
93
94	43
95	44
96	45
97	46
98
99
100

Scan	Original
71	32
72	33
73	34
74	35
75	36
76
77
78
79
80
81
82
83
84
85	37
86	38
87	39
88	40
89	41
90	42
91
92
93
94	43
95	44
96	45
97	46
98
99
100