260 On Marine Luminous Animals. 



can find their food. It is remarked by the Shetland fishermen, 

 that the ling invariably inhabits the deep valleys of the sea ; 

 whereas the cod is always found on the hills, general known by 

 the name of banks. In one of the most productive spots for 

 the ling fishery, the valley which they inhabit is not only very 

 deep, but is bounded by abrupt land or submarine hills nearly 

 precipitous ; the water suddenly deepening from 20 and 30 to 

 200 fathoms. In this, as well as in other valleys in which this 

 fishery is carried on, always very far from the shore, it is found 

 that the best fishing exists at the greatest depths, and it is not 

 unusual to sink the long lines in water of 250 fathoms depth. 

 The time required in setting and in drawing up from this depth, 

 the length of line used, which amounts in some cases even to 

 seven miles, is such as to prevent the fishermen from making any 

 attempts in deeper water ; but they are all of opinion that this 

 fish abounds most in the deepest places, and might advan- 

 tageously be fished for at much greater depths. Now allowing 

 even 1000 feet instead of Mr. Bouguer's calculation of 723, it is 

 plain that no light canexist in these valleys, and that the ling, like 

 other fish which prey in the deep seas, must have some means 

 of seeing his food, as well as of pursuing his social avocations 

 of whatever nature these may be. This can only be effected by 

 the luminous property, either of his prey, or of the animals 

 which abound in the sea, or else by that elicited from his own 



body. 



J. MAC CULLOCH. 

 Shetland, August, 1820. 



ART. IV. A Translation of KEY'S Essays on the Calci- 

 nation of Metals, &c. 



[Communicated by JOHN GEORGE CHILDREN, Esq., F.R.S., ^c.] 

 Continued from Page 83. 



ESSAY IV. 



Air and Fire have weight, and naturally descend. 

 HAD we as free a commerce with the elements of fire, as we 

 have with the air, we should doubtless, be furnished with ex- 

 periments, to confirm our assertion. True it is, that those 



