REFLECTION FROM THE SEA-BOTTOM. iJl 



sea," he says, " has very sensibly cliaiiged in colour 

 since our arrival upon the bank of Cape Agulhas this 

 morning. As we are sailing in the direction of 

 the current, which bears us rapidly along, this varia- 

 tion of tint cannot be ascribed to the colouring of the 

 water itself. We are compelled to conclude that it 

 is the eifect of the colour of the sea-bottom, the 

 yellowish tint of which, traversing the water, and 

 mingling with its normal blue, produces the greenish 

 hue that we have observed." As the depth is 

 between 600 and 700 feet at this point, the solar 

 light reflected from the bottom ha 1 traversed about 

 1300 feet of water without being extinguished ; since, 

 on being reflected back to the surface, it was still so 

 intense as to influence the colour of the water. 



The contradiction between this fact and the theory, 

 is only in appearance. Let two surfaces — the one 

 bright, but small in extent; the other less bright, 

 but of much larger size — be viewed through an im- 

 perfectly diaphanous body. Then let them be re- 

 moved to a distance simultaneously, and it will be 

 found that for a considerable time after the small 

 bright surface has disappeared, the larger an<l duller 

 will be visible. It is easy to perceive that the 

 colouring of the sea, as witnessed at Cape Agulhas, 

 is a phenomenon of the same kind. The bank is a 

 surface of very considerable extent, feebly illuminated, 



