M. Arago on the Colour of the Ocean. 333 



server a reflected atmospheric pencil, a great part of which, it 

 is true, will pass above his head. This portion would require 

 to be bent in its course, to be inflected, to be refracted from 

 above downwards to reach the eye. A second prism, placed 

 like the former, but nearer to the observer, would precisely 

 produce this effect. 



After these few words, every one, without doubt, has already 

 made the assimilation which must lead to the conclusion towards 

 which we are tending. The waves of the ocean are a kind of 

 prism ; no wave is ever solitary ; the continuous waves advance 

 nearly in parallel directions. Well, then, when two waves ap- 

 proach a vessel, a portion of the light which the anterior face of 

 the second wave reflects, traverses the first, is there refracted 

 from above downwards, and thus arrives at the observer placed 

 upon the deck. Again, then, we see transmitted light, light 

 which is consequently made greeuy reach the eye at the same 

 time with the common blue tints ; but these are the phenomena 

 of great depths over white sand produced without deep water, 

 and the green colour of the sea arises from the predominance 

 of the transmitted colour over the reflected colour. 



We have now thus hastily traced the imperfect lineaments of 

 a theory of the colours of the ocean, that thereby voyagers may 

 be directed in the studies they may have occasion to make on 

 the subject. The investigation of circumstances which may 

 oppose this theory will suggest to them experiments, or at least 

 observations, which without it they probably would not have 

 thought of. For example, every one will understand that the 

 prism waves should not produce identical effects, whatever may 

 be the direction of their propagation, and they will be led to 

 expect some variation in the hue of the sea upon a change of 

 the wind. Upon the lakes of Switzerland this phenomena is 

 apparent ; is it so also on the wide ocean ? 



Some persons persist in assigning an important influence to 

 the blue of the atmosphere in the production of the blue of the 

 ocean. It appears to us that this idea may be subjected to a 

 decisive proof; and in the following manner. The blue rays of 

 the atmosphere do not return from the water to the eye till after 

 they have been regularly reflected. If the angle of reflectiou 



VOL. XXV. NO. L. — OCTOBEK 1838. 2 



