PERSPECTIVE. 



481 



proportion to the intervening air. The nearest ob- 

 jects only appear in their true colours and full light. 

 In the case of the more distant, the light and colour 

 become blended with the colours of the vapours 

 which fill the air, in proportion to their distance, 

 until, at last, the objects become lost in an indistinct 

 mass, of a blueish tinge, in the horizon, whilst their 

 colour and that of the air become one. The pro- 

 portion of this degradation, as it is called, is regu- 

 lated by the purity of the air, being greater accord- 

 ing as there is more vapour in the air. Hence dis- 

 tant objects in a clear southern air appear much 

 nearer than they really are, to an eye accustomed to 

 a thick northern atmosphere. As the air changes, 

 the aerial perspective must change. Morning, noon, 

 evening, moonshine, winter, summer, the sea, &c., 

 all have their different aerial perspective. In aerial 

 perspective, the weakening of the tints corresponds 

 to the foreshortening of the receding lines in linear 

 perspective. In the illuminated parts of objects, the 

 tints are represented more broken and fluctuating. 

 The shaded parts are often aided by reflection. If 

 the degree of the density of the air is given, the de- 

 grees of these gradations may also be determined ; 

 not by mathematical rules indeed, but by close ob- 

 servation of nature. By aerial perspective two re- 

 sults are obtained: 1. Each object in a picture 

 receives that degree of colour and light which be- 

 longs to its distance from the eye : 2. The various 

 local tones are made to unite in one chief tone, which 

 is nothing else than the common colour of the air, 

 and the light which penetrates it. The charm and 

 harmony of a picture, particularly of a landscape, 

 depend greatly upon a correct application of aerial 

 perspective. Aerial perspective is hardly found at 

 all in the productions of the ancient German and 

 Italian schools to the time of Perugino. 



The methods of perspective commonly practised 

 are extremely complex and difficult to follow. 

 We have pleasure in presenting to the reader an 

 account of a method lately invented by Mr James 

 Whitelaw, Glasgow, who has favoured us with the 

 description and illustrations. The account will be 

 found clear and complete, and when it is recollected 

 that large volumes are necessary to explain per- 

 spective drawing on the old plan, the brevity of the 

 following account is a sufficient proof of the supe- 

 rior simplicity of the method it describes. 



1. If a person behind a transparent plane kept his 

 eye exactly in the same position till he traced on the 

 plane the objects on the other side of it by means of 

 a pencil carried over the parts of the plane where 

 the rays of light reflected to the eye from all the lines 

 in the objects cut the plane, the delineation would 

 be a perspective drawing of the objects. See i'l.LXV.* 



2. Fig. 24 is a ground plan of a number of objects, 

 marked a, b, c, d, standing on a horizontal surface ; 

 the same letters in fig. 25 point out the same objects 

 in the elevation; and fig. 26 is a perspective view of 

 them. Before going farther, I may remark, that 

 when a line is spoken of in this paper it is a straight 

 line that is meant, unless the contrary be mentioned. 



3. In order to draw the perspective view, make 

 first the ground plan and elevation as in figs. 1 and 

 2, then draw a line / g, in fig. 24, to represent the 

 transparent plane which stands perpendicular to the 

 surface on which the objects a, b, &c., stand, and 

 after this fix upon the point e, in the same fig. for 

 the position of the eye. But before making a full 

 view it may be as well to illustrate the method by 

 finding the perspective of a line, and as the line A 

 i, in fig. 24, plate LXV., which stands perpendicular 

 to the transparent plane is as good as any other, we 

 shall commence with it. The point h, which marks 

 the position of h i, in the elevation, is on a level 



with the eye. From the ends of the line h i, draw 

 the lines A e and i e to c, the point of sight, and the 

 part I h of the transparent plane, or picture sheet, 

 contained between the lines h e and i e, will be the 

 perspective in the ground plan of the line A f, be- 

 cause the lines A e and e e represent the rays of light 

 reflected to the eye from the ends of the line A i. 

 From what is now said, it will be evident that / n 

 shows the perspective in the ground plan of the part 

 i m, of the line A '; and n h is the perspective in 

 the same plan of A m, the other part of A i. If a 

 line be drawn through e, parallel to A i, till it meets 

 the picture-sheet in p; p h will show, in fig. 24, the 

 perspective of the line A i, if it is indefinitely ex- 

 tended beyond the point i. For, by inspecting the 

 ground plan, it will be seen that the more distant 

 from the picture-sheet any point ', is taken, the line 

 drawn from the point to the eye becomes more nearly 

 parallel to e p; and in consequence of this, p I be- 

 comes smaller, the more distant the point is taken. 

 And although we cannot name a distance from the 

 picture-sheet for the position of the point , that will 

 make p and / exactly coincide, yet we can place i 

 so distant, that the space betwixt p and / will be 

 smaller than any quantity that we can form a notion 

 of, and for tins reason p A must be considered the 

 perspective in the ground plan of the line A i, when 

 it is indefinitely extended from the point h, in fig. 24, 

 or from the point A, in the elevation which is on a 

 level with e, the point of sight in the same view. 



4. We now know how to represent on an edge 

 view of the transparent plane, or picture-sheet, the 

 perspective of any line, or part of a line, running 

 perpendicular to the transparent plane, and on the 

 same level with the eye ; but in order to make a 

 picture, the perspectives of the lines in the objects 

 to be represented, must be shown not on an edge, 

 but on an elevation of the picture-sheet. Let fig. 26 

 be this elevation; then through the lowest points of 

 the objects shown in fig. 25, draw the level I'me/g, 

 in figs. 25 and 26. The part offg, which is under the 

 elevation, will represent a horizontal surface, passing 

 through the lowest point of the objects to be shown 

 in perspective, and if the bottom ends of the objects 

 are on the same level as in figs. 24 and 25, this line 

 shows the horizontal surface on which the objects 

 stand, while the part of the line, _/"#, which passes 

 under the perspective view, will represent the inter- 

 section of the transparent plane with this horizontal 

 surface. I may remark just now, that the ground 

 plan is drawn in such a position that the line/ g, in 

 figs. 25 and 26, is parallel to the line marked/^-, in 

 fig. 24; and I may further notice, that these lines are 

 drawn parallel to the top or bottom edges of the 

 drawing-board, so that if a line is wanted to be 

 drawn either parallel or perpendicular to these lines, 

 the thing is done at once by applying a T square to 

 the edge of the drawing-board. If a line be drawn 

 perpendicular to/^, in figs. 25 and 26, through p, or, 

 which comes to the same thing, through e, in the 

 ground plan, and if another line be drawn through 

 e, which marks the place of the eye, as also the place 

 of the point p, in fig. 25, parallel to the same \\nefg, 

 and cutting the perpendicular line e e, in e; e, in the 

 perspective view, is the position of the point;?, shown 

 in the ground plan. Now, if we let fall perpendicu- 

 lar lines from the points A n and I, in fig. 24, to the 

 line/g-, in figs. 25 and 26, and then produce the hori- 

 zontal line e e, till it cuts the perpendicular lines A 

 q, n t, and / u, in the points A, m, and /, in fig. 26, 

 these points will be the perspectives of the points 

 marked A, m, and i, respectively, in the ground plan. 

 If the points A and /, in fig. 26, are joined, this line A 

 /, will be the perspective of the line A i, the part A 

 m, of this perspective line, is the perspective of the 

 2n 



