Gravesande, Willem Jacob 's - An essay on perspective

Scan	Original
31	10
32	11
33	12
34	13
35	14
36	15
37	16
38
39
40
41	17
42	18
43	19
44	20
45
46
47
48	21
49	22
50	23
51	24
52
53
54
55	25
56	26
57
58
59
60	27

5023on PERSPECTIVE. Perpendiculars f P, O H, muſt be let fall from
the Points f and O, on the Baſe Line, and the
Line P g drawn; then the Point V, wherein it
cuts the Perpendicular O H, is the Point of Sight
ſought, and the Parts O V, and V H determine
the Height and Diſtance of the Eye.

Method V.

35. When the Appearance of a Point is known,

Let A be a Point in the Geometrical Plane,
11Fig. 11. and a its Repreſentation in the perſpective Plane,
it is requir’d to find the Appearance of the
Point B.

Operation,
Without Compaſſes.

Draw a Line from the Point B to the Eye O,
and another from the Point E, wherein the
ſaid Line continued, cuts the Baſe Line, to the
Point A; then draw the Line E a, and where
it cuts B O, is the Point b ſought.

Demonstration.

The Point E is its own Repreſentation; and
becauſe the Point a is the Repreſentation of A,
the Line E a is that of E A. Now ſince the
Point B is in the Line E A, the Appearance of
this Point will be likewiſe in E a, as alſo 2227. B O; therefore it is in b the Interſection of the
Lines E a, and B O.

Remark.

37. If the Point A be in the Line B O, or
the Line B A be parallel, or a very little inclined
to the Baſe Line, we cannot then uſe this

Page concordance

Text layer

Text normalization

Search

Scan	Original
31	10
32	11
33	12
34	13
35	14
36	15
37	16
38
39
40
41	17
42	18
43	19
44	20
45
46
47
48	21
49	22
50	23
51	24
52
53
54
55	25
56	26
57
58
59
60	27

Scan	Original
31	10
32	11
33	12
34	13
35	14
36	15
37	16
38
39
40
41	17
42	18
43	19
44	20
45
46
47
48	21
49	22
50	23
51	24
52
53
54
55	25
56	26
57
58
59
60	27

Scan	Original
31	10
32	11
33	12
34	13
35	14
36	15
37	16
38
39
40
41	17
42	18
43	19
44	20
45
46
47
48	21
49	22
50	23
51	24
52
53
54
55	25
56	26
57
58
59
60	27