Gravesande, Willem Jacob 's - An essay on perspective

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17787on PERSPECTIVE.

Remarks.

What hath been obſerved on the Solar 11105. dows, hath no Regard to thoſe mentioned here:
For it matters not in this Problem, whether the
perſpective Plane be perpendicular, inclined, or
parallel; becauſe in theſe different Situations, the
two Points that are uſed may always be found.

Moreover, it muſt be obſerved, that the third
Problem takes in the Shadows of a ſmall 22106. as well as thoſe of the Sun; but not without this
Difference, that the Plane which in the third
Problem is ſuppoſed parallel to the Sun’s Rays,
ought here to be ſuppoſed to paſs through the
Light whoſe Shadows are ſought.

CHAP. VIII.

Of mechanically ſhortning the Operations of
Perſpective.

1. WHEN the perſpective Plane is ſup-
pos’d perpendicular or upright.

Problem I.

109. To find the Repreſentations of Figures in
the Geometrical Plane.

Let O be the Eye, R H the Baſe Line; F and
33Fig. 60 G the Points denoted with the ſame Letters in
Fig. 10.

4431.

Then take a Ruler and faſten to the Point G,
ſo that it may turn about the ſame in ſuch man.

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Scan	Original
81
82
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85	37
86	38
87	39
88	40
89	41
90	42
91
92
93
94	43
95	44
96	45
97	46
98
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100
101	47
102	48
103
104
105
106	49
107	50
108	51
109	52
110

Scan	Original
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
101	47
102	48
103
104
105
106	49
107	50
108	51
109	52
110