Gravesande, Willem Jacob 's - An essay on perspective

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14469on PERSPECTIVE. too obliquely, recourſe muſt be had to Problem I. 1181. to find the Appearance of a.

Method II.

85. A is the Foot of the Perpendicular: The
22Fig. 46. Triangle, E P M, is drawn as directed: 3382. T is the accidental Point of the Perpendiculars,
to the Geometrical Plane.

Operation.

Thro’ the Point a, the Appearance of A,
draw a Perpendicular to the Baſe Line; which
make equal in Repreſentation to the 4455. M E; in conſidering this laſt Line, as being
parallel to the Vertical Line. Then, from the
Extremity I of this Perſpective, to the Point of
Sight V, draw a Line cutting the Line T a, in
the Point X; which will be the Repreſentation
of the Extremity of the propos’d Line.

Demonstration.

Let us ſuppoſe a Line paſſing thro’ the Point
A, equal to M E, and parallel to the Verti-
cal Line. Suppoſe, moreover, that another Line
is drawn thro’ the Extremity of this Line, and
that of the propos’d Perpendicular; then this
laſt Line, by the Conſtruction of the Figure
M E P, will be parallel to the Station Line;
and conſequently, its Repreſentation will 5516. thro’ the Point of Sight; and its Interſection
with T a, will be the Extremity of the Repre-
ſentation ſought. But a I is the 6656. of the firſt Line, made equal to E M; and con-
ſequently, V I is that of the ſecond. Which was
to be demonſtrated.

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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

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