Gravesande, Willem Jacob 's - An essay on perspective

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9443on PERSPECTIVE. Priſm is greater than the Height of the Eye, the
precedent Method is the ſhorteſt.

Problem IX.

62. To throw a Concave Body into Perſpective.

11Fig. 28.

Having firſt ſound the Perſpective of the ſaid
Body, afterwards find the Appearance of its
Cavity, in conſidering the Cavity as a new
Body.

Problem X.

63. To throw a Sphere into Perſpective.

22Fig. 29.

Let A be the Seat of the Centre of the Sphere;
then the Point I the Perſpective of the Centre
muſt be found, and the Line IV drawn to 3350. Point of Sight V. This being done, raiſe V F per-
pendicular to V I, which make equal to the
Diſtance from the Eye to the perſpective Plane;
and in this Perpendicular continued, take V P
equal to the Diſtance from the Centre of the
Sphere to the perſpective Plane. Through the
Point P draw P Q parallel to V I cutting a Line
drawn from F through I, in Q; and about Q as
a Centre, with the Semidiameter of the Sphere,
draw the Circle C B, to which from the Point F,
draw the Tangents F C and F B, cutting the
Line I V in the Points G and E. On the Line
G E deſcribe the ſemicircle E D T G, wherein
draw the Line G D perpendicular to F I, which
biſect in H, and about H, as a Centre with the Ra-
dius H D, deſcribe the Arc of a Circle, L D R, cut-
ting the Line F I in the Points L and R. Take
the Chord G T in the Semicircle E D T G equal
to R L, and deſcribe a Semicircle T m G upon
G T; in which Semicircle draw ſeveral Lines,
as m n Perpendicular to G T; and cutting

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Scan	Original
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96	45
97	46
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106	49
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109	52
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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