Sheraton, Thomas; Bensley, Thomas; Mathews, James; Bensley, Thomas [Bearb.]; Mathews, James [Bearb.]; Terry, George [Bearb.]; Jordan, Jeremiah Samuel [Bearb.]; Wayland, L. [Bearb.]: The Cabinet-Maker And Upholsterer's Drawing-Book: In Three Parts (London: Printed For The Author, By T. Bensley; And Sold By J. Mathews ... C. Terry ... J.S. Jordan ... L. Wayland ... And By The Author, 1793)

( 206 )
Thus: let GR, Fig. 4, be the ground line, and HL the ho-
rizontal or vanifhing line, whofe height above the ground line
is equal to that of the eye of the fpediator; s is the center of the
pidture, and s D the diifance of the fpedfator’s eye from the ob-
ject b d. Draw db perpendicular and equal to BD, Fig. 1, and
as much to the right hand of j as D, in Fig. 1, is to e. Then, in
Fig. 4, draw the vifual lines d s and b s; which lines are to deter-
mine the heights of the two original objects, EC, FG, in Fig. 1.
Then take the fpaces DC, CG, from Fig. 1, and transfer them
to Fig. 4, from cfto and from a to on the ground line GR.
Draw the lines zz, D, n D, cutting the vifual line d s in g c; and
laftly, from g and e on the vifual j d, raife perpendiculars to j b;
then will g\f^ c, e be the perfpedtive representations of GF and
C B in Fig. 1.
The analogy between the two figures will appear as fol-
lows.—In optics, P, in Fig. 1, is the pupil, and Pe the diredt ra-
dial or axis of the eye, and equal to the diitance of the firlt
objedt D B from the eye. In perfpedtive, D, in Fig. 4, is the fame
as P in optics, Fig. 1; and, in Fig. 4, t, the center of the pidture
in perfpedtive, is the fame as e in Fig. 1. Therefore as P e in
optics is the diredl ray, and the diifance of the firfl objedt D B
from the pupil P, fo J D, Fig. 4, in perfpedtive, is the diftance
of the fpedfator’s eye from the pidture. In optics, if the fecond
objedt C E is removed twice as far from the eye P as the firft
8 objedt