108 



fourteenth or fifteenth degree. It would be 

 useless* to repeat these experiments when the at- 

 mosphere is loaded with clouds, or in the shadow 

 of a vessel. When, instead of directing the cya- 

 nometer toward a great extent of open sea, we 

 fix our eyes on a small part of it's surface through 

 a narrow aperture, the water appears of a beau- 

 tiful ultramarine color. Toward evening, on the 

 contrary, when the edges of the waves, illumined 

 by the Sun, are of an emerald green, their sur- 

 face, on the shady side, has a purple reflection. 



Nothing is more striking than the rapid 

 changes, which the ocean undergoes beneath a 

 serene sky, where no variations whatever are to 

 be perceived in the atmosphere. I do not here 

 speak of the whitish and milky tint, that marks 

 the waters of shoals, and in soundings, which is 

 owing only to the sand suspended in the liquid, 

 since it is perceived in places, where the bottom, 

 in twenty or thirty fathoms water, is no way vi- 

 sible ; I speak of those extraordinary changes, 

 by which, in the midst of the vast basin of the 

 equinoctial ocean, the water passes from an in- 

 digo blue to the deepest green, and from this to 

 a slate gray, without any apparent influence 

 from the azure of the sky, or the color of the 

 clouds. 



The blue tint of the ocean is almost independ- 

 ent of the reflection of the sky. In general the 

 sea between the tropics is of a more intense and 



