330 



COLOUR. 



brated statue of the Nile ; the four statues that sur- 

 round the splendid fountain and obelisk of the Piazza 

 Navona, the admired work of Bernini. They are 

 personifications of four of the principal rivers in the 

 world ; namely, the Ganges, which was sculptured 

 by Fran. Baratta ; the Nile, by Antonio Fancelli ; 

 the Danube, by Claude Franc; and the Rio de la 

 Plata, by Antonio Raggi. Other colossal statues of 

 less consequence are also found among the beautiful 

 works of art in this city. The pride and ambition of 

 the Roman emperors led them to encourage sculp- 

 tured representations of their persons. Nero was the 

 first who ventured on a colossus of himself by Zenodo- 

 rus ; but, after his death, it was dedicated to A polio 

 or the sun. Commodus afterwards took oft' the head, 

 and replaced it with a portrait of himself. Domitian, 

 actuated by a similar ambition, prepared a colossus 

 of himself as the deity of the sun. 



Among more modern works of this nature is the 

 enormous colossus of San Carlo Borromeo, at 

 Arona, in the Milanese territory. It is of bronze, (50 

 feet in height, and has a staircase, in its interior, for 

 the purpose of occasional repairs and restorations. 

 The bronze colossus, copied from one of the Monte 

 Cavallo statues, in Hyde park, London, and a few 

 but little larger than life, of the size that may be 

 termed heroic rather than colossal, such as decorate 

 some public buildings and commemorative columns, 

 as those on St Paul's cathedral ; lord Hill's column 

 in Shrewsbury; the Britannia, on the Nelson co- 

 lumn, at Yarmouth ; the duke of Bedford, in Russel 

 square; Charles Fox, in Bloomsbury square, &c., are 

 nearly all that Britain can boast of in this noble 

 style of art. The four colossal statues at Paris, which 

 are in front of the fagade of the palace of the corps 

 legislatif, are in good taste, and show great boldness 

 and freedom in the execution. They represent the 

 four greatest legislators of France Sully, Colbert, 

 L'Hopital, and D'Aguesseau. They are in their pro- 

 per costume, and seated. Canova's Perseus is also 

 much larger than life, and a very fine work. It be- 

 longs rather to the heroic than the colossal. 



COLOUR ; a property of light, the knowledge 

 of which can be obtained fronrno description, but is 

 acquired by means of the organ of sight. To investi- 

 gate the properties of light, so far as colour is concern- 

 ed, let us institute the following simple experiment : 

 Let a beam of light from the sun, be admitted 

 through a hole of the window-shut of a dark chamber. 

 At a little distance behind this hole let there be 

 placed a triangular glass prism in such a way as to 

 receive the beam of light, and transmit it to a white 

 wall opposite the window-shut. This arrangement 

 being made, it will be found that the beam of light, 

 after passing through the hole, remains white, and 

 proceeds in a straight line until it enters the prism, 

 on passing through which, however, it immediately 

 begins to disperse, and will form upon the wall an 

 oblong image of seven different colours ; red, orange, 

 yellow, green, blue, indigo, and violet. These 

 colours are precisely the same as those seen in the 

 rainbow (q. v.), and are called prismatic or primary 

 colours. Thus we see that the white light has been 

 decomposed into seven different colours, by means 

 of the glass prism, but if we place a screen, having 

 a hole in it, behind the prism, so as to intercept all 

 the light excepting that of one colour (say indigo), it 

 will be found that a prism placed behind the screen 

 will have no effect in decomposing this light ; so that 

 the indigo, in passing through the second prism, will 

 remain unchanged, and the same with all the others, 

 which led Newton to denominate the seven colours 

 above mentioned, simple or homogeneous colours. 

 That these seven primary colours, when combined 

 together in proper proportions, constitute white, 



may be shown by a very simple experiment. Let 

 the seven colours be painted on the fact of a circular 

 piece of pasteboard, as near their proper tints as pos- 

 sible, and in the order and proportion exhibited in 

 the diagram p. 331, where the circle being divided 

 into 360 degrees, the following spaces are allowed to 

 the respective colours, bearing the same propor- 

 tions as in the prismatic spectrum, and rainbow ; i. e. 

 violet 80, indigo 40, blue 60, green 60, yellow 48, 

 orange 27, red 45. If this painted circle be made 

 to whirl rapidly round its centre, no single colour 

 will have sufficient time to make a strong impression 

 on the eye before all the others have passed in 

 succession, the rays coming from the several colours 

 being in a manner minglea together, and the impres- 

 sion of the spectator will be that the circle is white. 

 The same thing may be proved by mixing, in due pro- 

 portion, seven powders of the proper colours, the com- 

 pound powder being white. Various theories have 

 been advanced to account for the phenomena of 

 colour, which the reader will find discussed under 

 our articles Light and Optics. A simple and satisfac- 

 tory theory may be deduced from the facts elicited 

 during the course of a series of experiments con- 

 ducted about the close of the last century by Lord 

 Brougham. From the experiments above alluded to 

 it is inferred that the particles which compose white 

 light vary in magnitude, the particles of the red 

 being to those ot the violet, in the proportion of 

 1275 to 1253 ; those two colours being the extremes 

 of the prismatic spectrum. The particles of all the 

 other colours, are less than the red, diminishing as 

 they approach the violet, the particles of which are 

 least. We may now see the cause of the prism 

 separating a beam of white light into seven different 

 colours, since it must have more power in altering 

 the course of the smaller particles than the larger or 

 more dense ; and, accordingly, we find the red rays 

 least bent out of their original direction, and the 

 violet most, the intermediate colours being more 

 or less bent from their primary course according as 

 they approach the red or violet. The cause of the 

 differences of colours hi bodies may also be easily 

 accounted for on the same principle. The pores of 

 some bodies are of such a nature, that they either 

 reflect all the rays of light which they receive or in 

 the proportions in which they exist in the solar 

 beams, in which case these bodies will appear white ; 

 when, on the other hand, they reflect none of the 

 rays they appear black. A remarkable proof of this 

 was given some years ago in the examination of a 

 specimen of crystal of quartz, about 2 inches in 

 diameter, belonging to the cabinet of the duchess of 

 Gordon.* This crystal being broken in two, the 

 faces of the fracture appeared perfectly black, pre- 

 senting an appearance like black velvet. On ex- 

 amination, this singular phenomenon was found to 

 arise from the smallness of the diameter of the fibres 

 not exceeding one-third of the millionth part of an 

 inch, in consequence of which they were incapable 

 of reflecting the smallest particles of the rays of 

 light. Between white and black, innumerable 

 species of colours may arise from the differences in 

 the magnitude and arrangement of the fibres and 

 pores ot the bodies which either reflect or transmit 

 light. The peculiarity of the fibrous arrangement oi 

 the surface of mother of pearl, causes it to reflect light 

 of different colours very agreeable to the eye ; a cir- 

 cumstance of which art has recently taken advan- 

 tage in producing similar appearances, by running 

 small grooves very near to each other across the 

 surface of polished glass or metal. That it is not 

 the chemical composition, but the mechanical ar. 

 rangement of the surface of the mother of pearl which 

 produces these colours, may be proved by a very 



