356 LECTURE XXXVIII. 



intervening objects ; so that a distant church in a woody and hilly country 

 appears more remote than if it were situated in a plain ; and for a similarr 

 reason, the apparent distance of an object seen at sea, is smaller than its 

 true distance. The city of London is unquestionably larger than Paris ; 

 but the difference appears at first sight much greater than it really is ; and 

 the smoke, produced by the coal fires of London, is probably the principal 

 cause of the deception. 



The sun, moon, and stars, are much less luminous when they are near 

 the horizon, than when they are more elevated, on account of the greater 

 quantity of their light that is intercepted, in its longer passage through 

 the atmosphere : we also observe a much greater variety of nearer objects 

 almost in the same direction : we cannot, therefore, help imagining them 

 to be more distant, when they rise or set, than at other times ; and since 

 they subtend the same angle, they appear to be actually larger. For similar 

 reasons the apparent figure of the starry heavens, even when free from 

 clouds, is that of a flattened vault, its summit appearing to be much nearer 

 to us than its horizontal parts, and any of the constellations seems to be 

 considerably larger when it is near the horizon than when in the zenith. * 

 (Plate XXX. Fig. 438.) 



The faculty of judging of the actual distance of objects is an impedi- 

 ment to the deception, which it is partly the business of a painter to pro- 

 duce. Some of the effects of objects at different distances may, however, 

 be imitated in painting on a plane surface. Thus, supposing the eye to be 

 accommodated to a given distance, objects at all other distances may be 

 represented with a certain indistinctness of outline, which would accom- 

 pany the images of the objects themselves on the retina : and this indis- 

 tinctness is so generally necessary, that its absence has the disagreeable 

 effect called hardness. The apparent magnitude of the subjects of our 

 design, and the relative situations of the intervening objects, may be so 

 imitated by the rules of geometrical perspective as to agree perfectly with 

 nature, and we may still further improve the representation of distance by 

 attending to the art of aerial perspective, which consists in a due observa- 

 tion of the loss of light, and the bluish tinge, occasioned by the interposi- 

 tion of a greater or less depth of air between us and the different parts of 

 the scenery. 



We cannot indeed so arrange the picture, that either the focal length 

 of the eye, or the position of the optical axes, may be such as would be 

 required by the actual objects : but we may place the picture at such a 

 distance that neither of these criterions can have much power in detecting 

 the fallacy ; or, by the interposition of a large lens, we may produce nearly 

 the same effects in the rays of light, as if they proceeded from a picture at 

 any required distance. In the panorama, which has lately been exhibited 

 in many parts of Europe, the effects of natural scenery are very closely 

 imitated : the deception is favoured by the absence of all other visible 

 objects, and by the faintness of the light, which assists in concealing the 

 defects of the representation, and for which the eye is usually prepared, by 



* Hooke on the Horizontal Moon, Birch, iii. 503, 507. 



