198 JURA. LUMINOUS ANIMALS. 



appearance is the result of atmospherical changes, and 

 that an universal brilliancy of the sea is the common 

 forerunner of a storm. Such changes may indeed cause 

 the animals to change their places with respect to the 

 surface ; but agitation of the water, whether by the motion 

 of a boat, of a net, of a fishing line, or of the waves them- 

 selves, will excite the light at any time, and thus alone 

 it appears connected with boisterous weather; not as a 

 forerunner, but as a necessary attendant on the disturbed 

 state of the ocean ; affording, in gales of wind and in other 

 favourable circumstances, the splendid, and, to landsmen, 

 the terrific appearance of a sea of fire. If any further 

 observation were requisite to confirm the opinion that 

 this appearance was not connected, either with future 

 changes of weather, or with any property inherent in the 

 sea itself, it would be sufficient to remark that it is most 

 conspicuous at those seasons of the year when the Medusae 

 are in greatest abundance. This is in the autumnal 

 season, when our bays and shores abound with the ani- 

 mals of this tribe, provided apparently by the arrange- 

 ments of Nature, for food to the migratory fishes which 

 then visit them; but which, like the migratory birds, 

 retire on the approach of winter to other seas or milder 

 climates. The luminous appearance of the sea diminishes 

 with the disappearance of the Medusae, and seems to 

 keep pace exactly, with the decay, or with the migration 

 or sinking to the bottom, of these prolific animals. 



With respect to the causes by which this light is excited, 

 or the circumstances under which it is elicited, it has 

 appeared to be invariably the result of the agitation or 

 disturbance of the animal, as it is of that of the sea when 

 the luminous matter exists in a detached state in the 

 water. But it seems also to be the effect of a volition 

 on its part ; whether this be the consequence of fear, 

 or of some other motive. When the sea contains Me- 

 dusae, although perfectly still, a frequent twinkling of 

 the lights is always to be seen; appearing and disap- 



