ii& PORT DESIRE, [CHAP. viii. 



make any observations on the subject. I may however add, that the 

 same torn and irregular particles of gelatinous matter, described by 

 Ehrenberg, seem in the southern as well as in the northern hemisphere, 

 to be the common cause of this phenomenon. The particles were so 

 minute as easily to pass through fine gauze ; yet many were distinctly 

 visible by the naked eye. The water when placed in a tumbler and 

 agitated, gave out sparks, but a small portion in a watch-glass scarcely 

 ever was luminous. Ehrenberg states that these particles all retain 

 a certain degree of irritability. My observations, some of which were 

 made directly alter taking up the water, gave a different result. I may 

 also mention, that having used the net during one night, I allowed it 

 to become partially dry, and having occasion twelve hours afterwards 

 to employ it again, I found 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 luminous 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 only 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 already 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 favoura?-** v. *^s production. Certainly I think the sea is most 

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

 whiC^i time it h a s swarmed with various animals. Observing that the 

 water charged with gelatinous particles is in an impure state, and that 

 the luminous Cppearance 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 r/f 

 the organic particles, by which process (one is tempted almost to call 

 it a kind of resoiration) the ocean becomes purified. 



December 23*^ We arrived at Port Desire, situated in lat. 47, or 



