### Full text

the Point of Sight.

### 113.1.

Plate. 17

This is done in aſſuming C H equal to {1/3}, or

{1/4} Part, & c. of the Diſtance from the Point C,

to the Foot of the vertical Line; and in raiſing

the Perpendicular H E, in the Point H, equal

to {1/3} or {1/4} Part, & c. of the Height of the Eye. Now A is a given Point, whoſe Appearance is

ſought.

## 114. Operation .

Draw a Parallel A B, through the Point A,

to the Baſe Line, meeting the Line C D in the

Point B, and let a ſecond Eye be ſuppoſed at

the ſame Height and Diſtance as the firſt; then

find F G the Repreſentation of A B for this
ſecond Eye, which continue until it meets the

Line C E in b, and in this Continuation aſſume

b a equal to F G; then a will be the Perſpective

ſought.

### 114.1.

## 115. Demonstration .

Becauſe the Height and Diſtance of the ſecond

Eye, is equal to the Height and Diſtance of the

firſt; the ſaid two Eyes are both in one parallel

Line A B; and conſequently , the Perſpective
of A B muſt be a Part of F G continued, and

alſo equal to F G: And therefore becauſe the
Perſpective of B is in the Line C E, a b is the

Perſpective of A B; and a , that of A. Which
was to be demonſtrated.

### 115.1.

78. Note, as to Lines perpendicular, and inclined

to the Geometrical Plane, ſee n. 76. This is

ſcarcely uſeful, unleſs for the Decorations of a

Theatre.