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 slso applied the cyanometer to measure 

 the colonr 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°. Wlien, 

 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 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. 



