440 COMPLEMENTARY COLOURS. DIRECTION OF MOVEMENTS. 



570. Upon these properties of the eye are founded the laws 

 of harmonious colouring ; a full knowledge of which should 

 be possessed by artists of every kind who are concerned with 

 contrasts of colour, whether in pictures, architectural decora- 

 tions, or even in dress. All complementary colours have an 

 agreeable effect when judiciously disposed in combination ; 

 and all bright colours which are not complementary have 

 a disagreeable effect, if they are predominant : this is espe- 

 cially the case in regard to the simple colours (red, blue, and 

 yellow), strong combinations of any two of which, without 

 any colour that is complementary to either of them, are ex- 

 tremely offensive. Painters who are ignorant of these laws, 

 introduce a large quantity of dull grey into their pictures, in 

 order to diminish the glaring effects which they would other- 

 wise produce ; but this benefit is obtained by a sacrifice of the 

 vividness and force which may be secured in combination 

 with the richest harmony, by proper attention to physiological 

 principles. 



571. The Eye is endowed with common sensibility ( 487) 

 .by the fifth pair of nerves ; and when this is paralysed, all 

 parts of it are completely insensible to the touch, although 

 the power of vision may remain unimpaired. It seldom pre- 



. serves its healthy condition in this state, however ; for the 

 . lachrymal and mucous secretions which protect its surface, are 

 no longer formed as they should be ; and inflammation, often 

 , terminating in the destruction of the eye, is the result. 



572. The visual sensations obtained through the Eye have 

 numerous and varied purposes among the lower animals. 

 That they chiefly serve to direct their movements, is evident 

 jrom observation of these movements ; and from the fact, 

 .that, when the eyes are covered or destroyed, most animals 

 make little attempt at determinate motions, though they fre- 

 quently exhibit a great deal of restlessness. There are a few 

 Vertebrata, however, which do not possess perfectly-formed 

 eyes, and which are consequently guided in their movements 

 by other senses. This is the case with the Mole, which 

 spends its whole life in burrowing beneath the ground ; and 

 also with the Proteus, and some others of the lower Am- 

 phibia, which inhabit the dark recesses of subterranean lakes 

 and channels. 



73. In the Articulated series of animals, we meet with 



