viii PHOSPHORESCENCE OF THE SEA 173 



the whole surface sparkled as brightly as when first taken out 

 of the water. It does not appear probable in this case that 

 the particles could have remained so long alive. On one 

 occasion having kept a jelly-fish of the genus Dianaea till it 

 was dead, the water in which it was placed became luminous. 

 When the waves scintillate with bright green sparks, I believe 

 it is generally owing to minute Crustacea. But there can be 

 no doubt that very many other pelagic animals, when alive, are 

 phosphorescent. 



On two occasions I have observed the sea lum.inous at 

 considerable depths beneath the surface. Near the mouth of 

 the Plata some circular and oval patches, from two to four 

 yards in diameter, and with defined outlines, shone with a 

 steady but pale light ; while the surrounding water onl)- gave 

 out a few sparks. The appearance resembled the reflection of 

 the moon, or some luminous body ; for the edges were sinuous 

 from the undulations of the surface. The ship, which drew 

 thirteen feet water, passed over, without disturbing these 

 patches. Therefore we must suppose that some animals were 

 congregated together at a greater depth than the bottom of 

 the vessel. 



Near Fernando Noronha the sea gave out light in flashes. 

 The appearance was very similar to that which might be 

 expected from a large fish moving rapidly through a luminous 

 fluid. To this cause the sailors attributed it ; at the time, 

 however, I entertained some doubts, on account of the frequency 

 and rapidity of the flashes. I have ahead}' remarked that the 

 phenomenon is very much more common in warm than in cold 

 countries ; and I have sometimes imagined that a disturbed 

 electrical condition of the atmosphere was most favourable to 

 its production. Certainl)- I think the sea is most luminous 

 after a few days of more calm weather than ordinary, during 

 which time it has swarmed with various animals. Observing 

 that the water charged with gelatinous particles is in an impure 

 state, and that the luminous appearance in all common cases 

 is produced by the agitation of the fluid in contact with the 

 atmosphere, I am inclined to consider that the phosphorescence 

 is the result of the decomposition of the organic particles, by 

 which process (one is tempted almost to call it a kind of 

 respiration) the ocean becomes purified. 



