ABSORPTION OF LIGHT. 127 



it, and this globe would roll on in darkness and silence, 

 without a vestige of vegetable form or of animal life. In 

 the Hebrew version of the Mosaic History, the reading 

 is, " Let light appear :" may not this really mean that 

 the earth's atmosphere was so cleared of obstructing 

 vapours, that the solar rays were enabled to reach the 

 earth? The same calculation supposes that sea- water 

 loses all its transparency at the depth of 730 feet ; but 

 a dim twilight must prevail much deeper in the ocean. 



The researches of Professor Edward Forbes have 

 proved, that at the depth of 230 fathoms in the ^Egeaii 

 sea, the few shelled animals that exist are colourless : no 

 plants are found within that zone ; and that industrious 

 naturalist fixes the zero of animal life of those waters at 

 about 300 fathoms.* Since these zones mark the rapidly 

 diminishing light, it is evident that where life ceases to be 

 must be beyond the limits to which life can penetrate. 



* Report an the Mollusca and Radiata of the jEgean Sea, and 

 on their distribution, considered as bearing on Geology. By Edward 

 Forbes, F.R.S.,&c. Reports of the British Association, vol. xii. Pro- 

 fessor Forbes remarks : " A comparison of the testacea, and other 

 animals of the lowest zones, with those of the higher, exhibits a 

 very .great distinction in the hues of the species, those of the 

 depths being, for the most part, white or colourless, while those of 

 the higher regions, in a great number of instances, exhibit brilliant 

 combinations of colour. 'The results of an enquiry into this sub- 

 ject are as follows : 



"The majority of shells of the lowest -zone are white or trans- 

 parent; if tinted rose is the hue, a very few exhibit markings of 

 another colour. Tii the seventh region, white species are also 

 very abundant, though by no means forming a proportion so great 

 as the eighth. Brownish red, the prevalent hue of the brachio- 

 poda, also givBS a character of colour to the fauna of this zone; 

 the Crustacea found in it are red. In the sixth zone the colours 

 become brighter, reds and yellows prevailing, generality, how- 

 ever, uniformly colouring tlie shell. In the fifth region many 

 species are bamled or clouded with various combinations of -colours, 

 and the number of white species has greatly diminished, lu the 

 fourth, purple hues are frequent, and 'Contrasts of colour common. 

 In the second and third, green and blue tints are met with, some- 



