THE VOYAGE OF THE BEAGLE 177 



After the elaborate paper, 8 by Ehrenberg, on the phos- 

 phorescence of the sea, it is almost superfluous on my part 

 to 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 after 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 reflec- 

 tion of the moon, or some luminous body ; for the edges were 

 sinuous from the undulations of the surface. The ship, 

 which drew thirteen feet of water, passed over, without dis- 

 turbing 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. 



8 An abstract is given in No. IV. of the Magazine of Zoology and Botany. 



