58 COLOUR OF THE OCEAN. 



pilots transmit to each other, several evince great 

 sagacity. Prognostics are also in general less un- 

 certain on the ocean, and especially in the equinoc- 

 tial parts of it, than on land, where the inequalities 

 of the ground interrupt the regularity of their mani- 

 festation. 



Humboldt also applied the cyanometer to measure 

 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 aper- 

 ture, 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 changes 

 which the colour of the sea undergoes under a clear 

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

 when it maybe seen passing from irn c ^o-blue to the 

 deepest green, and from .j&is 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. 



