NINTH DAY.] COLOUR OF THE OCEAN. 277 



ORN. On what then does the tint of the ocean 

 depend, which has itself given name to a colour ?* 



HAL. I think probably on vegetable matter, and, 

 perhaps, partially on two elementary principles, iodine 

 and brome, which it certainly contains, though these 

 are possibly the results of decayed marine vegetables. 

 These give a yellow tint, when dissolved in minute 

 portions in water, and this, mixed with the blue of 

 pure water, would occasion sea green. I made, many 

 years ago, being on the Her de Glace, an experiment 

 on this subject. I threw a small quantity of iodine, 

 a substance then recently discovered, into one of those 

 deep blue basins of water, which are so frequent on 



[* The colour of the ocean out of soundiags is blue, indeed blue 

 water in the sailor's vocabulary is equivalent to being out of soundings. 

 In shallow seas, in which light is reflected from the bottom, the 

 various tints of the surface may be considered as depending chiefly on 

 the modifying influence of the rays so reflected, being greenish, when 

 the bottom is yellow, &c. At one time the blue colour of the ocean 

 \vas supposed to be owing to the reflected hue of the atmosphere. 

 That it is a property of the water itself, I have had proof, and often, 

 in ocean voyages. The following is from a sea journal kept in 1820, 

 when returning from Ceylon, and may be adduced in proof: referring 

 to a gale, when no blue sky was to be seen, it is observed, " during 

 this gale the sky was overcast, so as to be of the dark grey or light 

 sooty hue, but the sea retained its usual colour. Its blue colour 

 appeared very distinct, when one looked immediately down from the 

 ship into the sea ; and it was equally evident in the waves as they 

 rose, their heads being between the light and eye of the observer. 

 Even in the colour of the surface of the sea in general, a tint of blue 

 might be distinguished, but it was not bright on account of the dark- 

 ness of the surface." J. D.] 



