PERSPECTIVE. 



parts, they have the same effect, *nd 

 compel us to have recourse to various 

 vanishing points, in which we seek the 

 termination of those lines that converge, 

 and in fact divide the building, though 

 full fronted and uniform, into several 

 parts ; each of which seems to assume a 

 distinct character, and to demand sepa- 

 rate consideration This will be more 

 fully understood when we treat of the 

 general rules which govern perspective. 

 The reader must recollect, that, as it 

 would be impossible to represent more 

 than one view of the object, in one 

 plane, or picture, so there can be but 

 one point of sight ; that is, but one par- 

 ticular spot, where the eye of the spec- 

 tator is supposed to be fixed; from 

 which, as from a very minute point, all 

 the figures represented must appear as 

 under one general system. The same 

 attention must of course be paid to 

 shadows ; for we cannot suppose the dark 

 side of a house to result from any thing 

 but the light being in such a quarter as 

 does not allow it to strike on that side ; 

 consequently we attribute the bright 

 side of ihe same object to its being illu- 

 minated by the rays which act peremp- 

 torily upon it. Speaking of common ef- 

 fects, we consider the light to be solita- 

 ry ; such as the Sun, or the Moon, or one 

 candle, &c. ; hence we perceive both 

 the necessity, and the reason, for ex- 

 hibiting all objects as bright, which are 

 within the range of, or shew themselves 

 openly to, the light, and all parts to which 

 its rays cannot reach direct, as being in 

 the shade and more or less dark accord- 

 ing as they may be more retired and con- 

 fined. When two lights are found in the 

 same picture, such as two candles on a 

 table, there will be to every object un- 

 der their mutual influence a half shade, 

 and a whole shade ; the former called the 

 penumbra, shewing tljat extent which re- 

 sults 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 the 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 \vili increase with the remote- 

 ness of the plane, or wall, on which it is 

 represented. 



The following definitions of the prin- 

 cipal features in the science and applica- 

 tion of perspective will prove useful to 

 iiz. projection delineates 



objects in piano, by means of right Tines 

 called rays, supposed to be drawn from 

 every angle of the object to particular 

 points. When the objects are angular, 

 these rays necessarily form pyramids, 

 having the plane or superficies, whence 

 they proceed, for their basis ; but when 

 drawn from, or to, circular objects, they 

 form a cone. 



Ichnography, or ichnographic projec- 

 tion, is described by right lines parallel 

 among themselves, and perpendicular to 

 the horizon, from every angle of every 

 object, on a plane parallel to the hori- 

 zon. The points where the perpendicu- 

 lar lines or rays cut that plane being 

 joined by right lines. The figure pro- 

 jected on the horizontal plane is likewise 

 called the plan or seat of that object on 

 the ground plane. The points are the 

 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 super- 

 structures stand, or are supported ; and 

 we are further enabled to judge of, in- 

 deed to measure, their several parts, and 

 their areas 



Orthography represents the vertical 

 position and appearance of an object ; 

 hence orthographic projection is called 

 the elevation. 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 divided 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 ob- 

 lique section. 



These give us the modes of laying 

 down plans, of shewing the parts, and 

 the manner in which the interiors of 

 edifices are arranged ; 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. scenography, 

 which shews us how to direct the visual 

 rays to every point, or part, of a pic- 

 ture ; and stereography, which enables 

 us to represent solids on a plane, from 

 geometrical projection ; whence their se- 

 veral dimensions, viz. length, breadth, 

 and thickness, may all be represented* 

 and be correctly understood at sight. 



