VOYAGE TO ALGKUIA. 127 



opinion, scatter no light at all. The track of a luminous 

 beam could not be seen in such water. But "an amount 

 of impurity so infinitesimal as to be scarcely expressible in 

 numbers, and the individual particles of which are so small 

 as wholly to elude the microscope, may, when examined by 

 the method alluded to, produce not only sensible, but strik- 

 ing effects upon the eye." 



The result of the examination of nineteen bottles filled 

 at various places between Gibraltar and Spithead, are 

 here tabulated: 



NO. LOCALITY COLOR OF SEA 



APPEARANCE IN LUMINOUS 

 BEAM 



1 Gibraltar Harbor* Green Thick with fine particles 



2 Two miles from Gibraltar Clearer green. . . . Thick with very fine particles 



" Off Cabreta Point Bright green. 



4 Off Cabreta Point Black-indigo . . 



5 Off Tarifa Undecided 



(5 Bey oud Tarifa Cobalt-blue 



7 Twelve miles from Cadiz. ... . .Yellow-green. . 



8 Cadiz Harbor Yellow-green . . 



9 Fourteen mi les from Cadiz . . . Yellow-green . . 



10 Fourteen miles from Cadiz. . Bright green.. 



11 Between Capes St. Mary and 



Vincent Deep indigo . . . 



12 Off the Burlings Strong green . . 



13 Beyond the Burlings Indigo 



14 Off Cape Finisterre Undecided 



..Still thick, but 



..Much less thick, very pure 



. .Thicker than No. 4 



. . Much purer than No. 5 



..Very thick 



. . Exceedingly thick 



..Thick, but less so 



. . Much less thick 



. . Very little matter, very pure 

 . .Thick, with fine matter 

 . .Very little matter, pure 

 ..Less pure 



15 Bay of Biscay Black-indigo . . . .Very little matter, very pure 



16 Bay of Biscay Indigo Very fine matter. Iridescent 



17 Off Ushant Dark green A good deal of matter 



18 Off St. Catherine's Yellow-green Exceedingly thick 



19 Spithead Green Exceedingly thick 



Here we have three specimens of water, described as 

 green, a clearer green, and bright green, taken in Gibraltar 

 harbor, at a point two miles from the harbor, and off 

 Cabreta Point. The home examination showed the first 

 to be thick with suspended matter, the second less thick, 

 and the third still less thick. Thus the green brightened 

 as the suspended matter diminished in amount. 



Previous to the fourth observation our excellent navigat- 

 ing lieutenant, Mr. Brown, steered along the coast, thus 

 avoiding the adverse current which sets in, through the 

 strait, from the Atlantic to the Mediterranean. He was at 

 length forced to cross the boundary of the Atlantic current, 

 whicii was defined with extraordinary sharpness. On the 

 one side of it the water was a vivid green, on the other a 

 deep blue. Standing at the bow of the ship, a bottle could 

 be filled with blue water, while at the same moment a 

 bottle cast from the stern could be iiiied with green water. 



