PERSrECTIVE. 
parallel to any original lines, and produced 
until they touch the picture. 
Ground plane is the surface of the earth, 
or plane of the horizon, on which the pic- 
ture is supposed to stand. 
The ground line is that formed by the 
intersection of the picture in the ground 
plane. 
The horizontal line is the vanishing point 
of the horizontal plane, and is produced in 
the same manner as any other vanishing 
line, viz, by passing a plane through the eye 
parallel to the horizontal plane. 
The point of sight is the fixed point from 
which the spectator views the perspective 
plane. 
Vanishing points are the points which are 
marked down in the picture, by supposing 
lines to be drawn from the spectator’s eye, 
parallel to any original lines, and produced 
until they touch the picture. 
The centre of a picture is that point 
on the perspective plane where a line, 
drawn from the eye pei-pendicular to the 
picture, would cut it ; consequently it is 
that part of the picture which is nearest to 
the eye of the spectator. 
The distance of the picture is the dis- 
tance from the eye to the centre of the 
picture. If what has been already said 
and repeated, regarding the angle of 60 
degrees, is understood, the spectator will 
never bring the picture so near to himselt 
as to occasion the eyes to expand, indeed 
to strain, so as to embrace more than that 
angle. 
The distance of a vanishing point is the 
distance from the eye of the spectator to 
that point where the converging lines meet, 
and after gradually diminishing all the ob- 
jects which corae within their direction and 
proportion, are reduced so as in fact to 
terminate in nothing. All parallel lines have 
the same vanishing point ; that is to say, all 
such as are in a building, parallel to each 
other, when not represented exactly oppo- 
site to, and parallel with the eye, will appear 
to converge towards some remote point, i. e. 
their vanishing point. Circles, when retir- 
ing in such manner, are represented by 
ellipses, proportioned to their distances : 
their dimensions in perspective are ascer- 
tained by enclosing them, or the nearest of 
them, where a regular succession is to be 
pourtrayed within a square, which being 
divided into any number of equal parts or 
chequers, will show all the proportions of 
those more remote. We trust it scarcely 
requires to be repeated that the further any 
object is from the eye or fore-ground of a 
picture, the less it will appear in nature, 
and the more it must be reduced in exhi- 
biting its perspective. 
A bird’s-eye view is supposed to be taken 
from some elevated spot which commands 
such a prospect as nearly resembles the 
plane or ichnography of the places seen. 
Thus the view from a high tower, or from 
a mountain, whence the altitudes of the 
several objects on the plane below appear 
much diminished, gives nearly the same 
representation as is offered to a bird flying 
over them ; whence the term. Some idea 
may be formed of- this by standing on any 
height, and observing how low those ob- 
jects, which are near thereto, will appear 
when compared with those more distant, 
taking, however, the perspective diminu- 
tion of the latter into consideration. , 
We shall now explain the five figures in- 
cluded in the Plate of Perspective. The 
first figure shews a base line, A B, divided 
into eight equal parts, whose perspective 
proportions on the lines A C and B C, are 
shewn by drawing, from the several divi- 
sions, 1, 2, 3, 4, &c. on A B, rays to the 
vanishing points, D and E, situated on the 
horizon. If A C and B C were of equal 
length, the several squares- thus made in the 
area, A C B, would shew trapezia regularly 
diminishing towards C, having their oppo- 
site angles intersectable by perpendiculars 
from the base line, A B, and the other op- 
posite angles intersectable by horizontal 
lines parallel to A B. But A C being longer 
than B C, gives the whole of the trapezia 
a cast towards E. This shews that the 
two vanishing points, while, (in this in- 
stance) they serve to intersect each other, 
contain distances, considered perspectively, 
in proportion to their brevity ; they are un- 
der the same parallels, but the angle, 
BAG, being smaller than the angle, C B A, 
causes the divisions on A C to be more ex- 
tensive than those on B C, as may be seen 
by referring to the lesser spaces occupied 
by the standard on the latter. The figures 
1, 2, 3, &c. correspond with those on the 
base line, exhibiting their due perspestive 
distances on the lines A C and B C. It 
will also be observed, that as the trapezia 
become more distant, they become smaller, 
while their angles pointing towards C, and 
towards the base line, that is, their per- 
pendicular angles become more obtuse, and 
their horizontal angles, i. e. those on the 
right and left, become more acute : were 
it otherwise, they could not produce a 
