COLOUR OF THE OCEAN. 59 



conpectcd with those atmospherical changes that take chap, iv 

 place after eight or ten hours. 



Mariners, are accustomed to observe the appearances Ji;>riners 

 of the sky more carefully tlian landsmen, and among cat^is! '' 

 the numerous meteorological rules which pilots transmit 

 to each other, several evince great sagacity. Prognostics 

 are also in general less uncertain on the ocean, and 

 especially in the equinoctial parts of it, than on land, 

 where the inequalities of the ground interrupt the re- 

 gularity of their manifestation. 



Humboldt also applied the cyanometer to measure Colo-ar of 

 the colour of the sea. In fine calm weather, the tint ^^^ 

 was found to be equal to 33°, 38°, sometimes even 44° 

 of the instrument, although the sky was very pale, and 

 scarcely attained 14^ or 15°. When, instead of directing 

 the apparatus to a great extent of open sea, the observer 

 fixes his eyes on a small part of its surface viewed 

 through a narrow aperture, the water appears of a rich 

 ultramarine colour. Towards evening again, when the 

 edge of the waves, as the sun shines upon them, is of an 

 emerald-green, the surface of the shaded side reflects a 

 purple hue. Nothing is more striking than the rapid Rapid 

 changes which the colour of the sea undergoes under a -^'^^'ises- 

 clear sky, in the midst of the ocean and in deep water, 

 when it may be seen passing from indigo-blue to the 

 deepest green, and from this to slate-gray. The blue is 

 almost independent of the reflection of the atmosphere. 

 The intertropical seas are in general of a deeper and 

 purer tint than in high latitudes, and the ocean often 

 remains blue, when, in fine weather, more than four- 

 fifths of the sky are covered with light and scattered 

 clouds of a white colour. 



