180 FRAGMENTS OF SCIENCE 



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 nav- 

 igating 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, which 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 filled with 

 green water. Two bottles were secured, one on each side 

 of this remarkable boundary. In the distance the At- 

 lantic had the hue called ultramarine; but looked fairly 

 down upon, it was of almost inky blackness — black quali- 

 fied by a trace of indigo. 



What change does the home examination here reveal? 

 In passing to indigo, the water becomes suddenly aug- 

 mented in purity, the suspended matter becoming sud- 

 denly less. Off Tarifa, the deep indigo disappears, and 

 the sea is undecided in color. Accompanying this change, 

 we have a rise in the quantity of suspended matter. Be- 

 yond Tarifa, we change to cobalt-blue, the suspended 

 matter falling at the same time in quantity. This water 

 is distinctly purer than the green. We approach Cadiz, 

 and at twelve miles from the city get into yellow- green 

 water; this the London examination shows to be thick 

 with suspended matter. The same is true of Cadiz Har- 

 bor, and also of a point fourteen miles from Cadiz in the 



