PERSPECTIVE. 
as being in tlie shade, and more or less dark 
according as tliey may be more retired and 
confined. When two lights are found in the 
same picture, such as two candles on a 
table, there will be to every object nnder 
their mutual influence a half shade, and a 
whole shade; the former called the pe- 
numbra, shewing that extent which results 
from one light being obscured, or cut off ; 
and the latter or the umbra, shewing those 
parts which are not acted upon by either of 
tlie lights. This will be obvious to any 
person who may place two candles behind 
him, as he sits with his back to a table ; they 
being about two feet asunder. He will 
then see, on the wall, the influence of each 
candle ; and his shadow will increase with 
the remoteness of the plane, or wall, on 
which it is represented. 
The following definitions of the principle 
features in the science and application of 
perspective will prove useful to the student, 
ciz. projection delineates objects in piano, 
by means of right lines called rays, supposed 
to be drawn from every angle of the object, 
to particular points. When the objects are 
angular, these rays necessarily form pyra- 
mids, having the plane or superfices, whence 
they proceed for tlieir basis ; but when 
drawn from, or to, circular objects, they 
form a cone. 
Ichnography, or ichnographic projection, 
is described by right lines parallel among 
themselves, and perpendicTiuar to the ho- 
rizon, from every angle of every object, on 
a plane parallel to the horizon. The points 
where the perpendicular lines or rays cut 
that plane being joined by right lines. The 
figure projected on the horizontal plane is 
likewise called the plan, or seat of that ob- 
ject on the ground plane. The points are 
tbe scites, or seats, of the angles of the ob- 
ject. The lines are the seats of the sides. 
By this we are to understand how the basis 
of figures represented' as superstructures 
stand, or are supported ; and we are further 
enabled to judge of, indeed to measure, 
their several parts, and their areas. 
Orthography represents the vertical posi- 
tion and appearance of an object; hence 
orthographic projection is called the eleva- 
tion. When we thus see the front of a house, 
we give it that term ; but when the side is 
displayed, we call it the profile. If we 
suppose a house, or other object to be di- 
vided by a plane passing perpendicularly 
through it in a line at right angles with the 
point, we call it the lateral section ; but if 
the plane pass in a direction parallel with 
the front, it is termed a longitudinal section. 
If the plane passes in neither of the former 
directions (not however deviating from 
the vertical) it is said to be an oblique 
section. 
These give us the modes of laying down 
plans, of shewing the parts, and the manner 
in which the interiors of edifices are ar- 
ranged ; consequently are indispensable to 
the architect, surveyor, and indeed should 
be understood by every person in any way 
connected with building, or designing. Nor 
should the following be neglected, viz. sce- 
nography, which shews us how to direct the 
visual rays to every point, or part, of a 
picture ; and stereography, which enables 
ns to represent solids on a plane, from geo- 
metrical projection ; whence their several 
dimensions, viz. length, breadth, and thick- 
ness may all be represented, and be cor- 
rectly understood at sight. We suppose 
our readers to have some knowledge of 
geometry before they commence upon this, 
or any other of the abstract sciences which 
are founded thereon. Should such, how- 
ever, not be the case, we beg leave to refer 
them to that head, where they will find suf- 
ficient instruction to enable them to prose- 
cute their enquiries on the subject now be- 
fore us. 
An original object, is that which becomes 
the subject of the picture, and which is the 
parent of the design. Any plane figure 
may become an object, as may any of its 
parts, as a broken pillar, the ruins of a 
house, the stump ov the branch of a tree ; 
but we generally speak of objects as relat- 
ing to entire figures represented as solids, 
or to as much rural or other scenery as 
may be embraced under an angle of 60 de- 
grees formed by two lines meeting at the 
eye. This will explain why we are enabled 
to represent so great a number of distant 
objects, while the front, or fore-ground, 
will contain, comparatively, but a very few : 
it being obvious that as the lines forming 
the angle become more distant, the more 
may be included between them. 
Original planes, or lines, are the surfaces 
of the objects to be drawn ; or they are 
any lines of those surfaces ; or it means the 
surfaces on which these objects stand. 
Perspective plane is the picture itself, 
which is supposed to be a transparent plane, 
through which we view the objects repre- 
sented thereon. 
Vanishing planes are those points which 
are marked upon the picture, by supposing 
lines to be drawn from the spectator’s eye 
