282 RECEXT PEOGRESS OF THE THEORY OF YISIOX. 



standing at diiSferent distances from the spectator. It is 

 part of a painter's merit for his figures to stand out 

 boldly. Now how does he produce the illusion? We 

 shall find, in the first place, that in painting a landscape 

 he likes to have the sun near the horizon, which gives 

 him strong shadows ; for these throw objects in the 

 foreground into bold relief. Next he prefers an atmo- 

 sphere which is not quite clear, because slight obscurity 

 makes the distance appear far off. Then he is fond of 

 bringing in figures of men and cattle, because, by help of 

 these objects of known size, we can easily measure the 

 size and distance of other parts of the scene. Lastly, 

 houses and other regular productions of art are also 

 useful for giving a clue to the meaning of the picture, 

 since they enable us easily to recognise the position of 

 horizontal surfaces. The representation of solid forms 

 by drawings in correct perspective is most successful in 

 the case of objects of regular and symmetrical shape, 

 such as buildings, machines, and implements of various 

 kinds. For we know that all of these are chiefly bounded 

 either by planes which meet at a right angle or by 

 spherical and cylindrical surfaces ; and this is sufficient 

 to supply what the drawing does not directly show. 

 Moreover, in the case of figures of men or animals, our 

 knowledge that the two sides are symmetrical further 

 assists the impression conveyed. 



But objects of unknown and irregular shape, as rocks 

 or masses of ice, baffle the skill of the most consummate 

 artist ; and even their representation in the most com- 

 plete and perfect manner possible, by means of photo- 

 graphy, often shows nothing but a confused mass of 

 black and white. Yet, when we have these objects in 

 reality before our eyes, a single glance is enough for 

 us to recognise their form. 



The first who clearly showed in what points it is 



