18 PHYSICAL GEOGKAPHY OP THE SEA. 



sea-water, must be set vertically on a white plate, and then, 

 looking through the open end, you will see the white of the 

 porcelain changed into a light blue tint. 



In the Grulf of Naples, we find the inherent colour of the 

 water exhibited to us by Nature on a most magnificent scale. 

 The splendid " Azure cave," at Capri, might almost be said tc- 

 have been created for the purpose. For many centuries its 

 beauties had been veiled from man, as the narrow entrance is 

 only a few feet above the level of the sea, and it was only 

 discovered in the year 1826, by two Prussian artists accidentally 

 swimming in the neighbourhood. Having passed the portal, 

 the cave widens to grand proportions, 125 feet long, and 145 

 feet broad, and except a small landing place on a projecting rock 

 at the farther end, its precipitous walls are on all sides bathed 

 by the influx of the waters, which in that sea are most remarkably 

 clear, so that the smallest objects may be distinctly seen on the 

 light bottom at a depth of several hundred feet. All the light 

 that enters the grotto must penetrate the whole depth of the 

 waters, probably several hundred feet, before it can be re- 

 flected into the cave from the clear bottom, and it thus 

 acquires so deep a tinge from the vast body of water through 

 which it has passed, that the dark walls of the cavern are 

 illumined by a radiance of the purest azure, and the most 

 differently coloured objects below the surface of the water are 

 made to appear bright blue. Had Byron known of the exist- 

 ence of this magic cave, Childe Harold would surely have sung 

 its beauties in some of his most brilliant stanzas. 



All profound and clear seas are more or less of a deep blue 

 colour, while, according to seamen, a green colour indicates 

 soundings. The bright blue of the Mediterranean, so often 

 vaunted by poets, is found all over the deep pure ocean, not 

 only in the tropical and temperate zones, but also in the regions 

 of eternal frost. Scoresby speaks with enthusiasm of the splendid 

 blue of the Greenland seas, and all along the great ice-barrier 

 which under 77° S. lat. obstructed the progress of Sir James 

 Boss towards the pole, that illustrious navigator found the waters 

 of as deep a blue as in the classical Mediterranean. The North 

 Sea is green, partly from its water not being so clear, and partly 

 from the reflection of its sandy bottom mixing with the essen- 

 tially blue tint of the water. In the Bay of Loanga the sea has 



