166. The eye has an undoubted pleasure in seeing colours, independently of the design and every other quality of the object which displays them. A suitable example to demonstrate this, is the wainscoting of an apartment in one or more flat tints which only attract the eyes and affect them more or less agreeably, as the colours are well or badly chosen. 167. First Case. _Agreeable Colour._—Every one, whose eyes are well organized, derives pleasure from looking at the coloured rays transmitted through a coloured glass, whether it be red, orange, yellow, green, blue, or violet. 168. Second Case. _Different Tones of the same Scale of Colour._—The simultaneous view of the series of tones of the same scale, which commences with white and ends with dark brown, gives undoubtedly an agreeable sensation, especially if the tones have equal and sufficiently numerous intervals; for example, from eighteen to thirty. 169. Third Case. _View of Different Colours, belonging to adjacent Scales, assorted conformably to Contrast._—The simultaneous view of different colours, belonging to scales more or less allied to each other, may be agreeable; but the assortment of scales producing this effect is very difficult to obtain, because the more nearly the scales approach, the more frequently it happens that one of the colours injures that which is adjacent to it, and even both are reciprocally injurious. The painter may, however, take advantage of this harmony, by sacrificing one of the colours, which he subdues, to make the other more brilliant. 170. Fourth Case. _View of very different Colours, belonging to very distant Scales, arranged conformably to Contrast._—The simultaneous view of complementary colours, or of binary assemblages of colours, which, without being complementary, are yet very different, is also an undoubtedly agreeable sensation. 171. Fifth Case. _View of various Colours, assorted more or less according to the Law of Contrast_, being seen through a glass of a colour not deep enough to allow all the colours peculiar to the glass to be visible, afford a spectacle which is not without its charm, and which is placed between that produced by the tones of the same scale, and that which is produced by various colours; for it is evident, that if the glass were of a deeper colour, it would cause objects to be seen of the colour peculiar to it. 172. Hence we infer that there are six distinct harmonies of colour, comprised in two species.