Gravesande, Willem Jacob 's - An essay on perspective

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18592An ESSAY

II. When the Perſpective Plane is inclined.

Prob. III.

115. To find the Repreſentation of Figures which
are in the Geometrical Plane.

The Operation laid down for the 11109,
110. Plane being perpendicular, may be uſed here,
becauſe the inclined perſpective Plane may be
changed into a perpendicular or upright one.

2281.

Prob. IV.

116. To find the Appearances of any Number of
Lines of the ſame Length, which are perpendicular
to the Geometrical Plane.

Raiſe a Perpendicular R C, in ſome Point on
33Fig. 62. the Baſe Line, in which aſſume R L equal in
Length to the given Lines; and draw the Line
L P, through the Point L, ſo that the Angle
L P R, be equal to the Angle of Inclination of
the perſpective Plane; then having made R S
equal to P L, and S C equal to P R, draw the
Lines S Q and C D, parallel to the Baſe Line.
This being done, raiſe up the Figures of the
Geometrical Plane, ſo that the Point R coincides
with c, and the Line R H, with C D; then
proceed as is directed for the 44112, 113. perſpective Plane, in uſing S Q for the Baſe
Line.

This is demonſtrated in n. 114.

Remarks.

The Point C muſt be aſſumed below the Point
S, when the perſpective Plane is inclined

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Scan	Original
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
151	73
152	74
153
154
155
156	75
157	76
158
159
160

Scan	Original
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
151	73
152	74
153
154
155
156	75
157	76
158
159
160

Scan	Original
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
151	73
152	74
153
154
155
156	75
157	76
158
159
160