gitudes towards the Brazilian coast perpetually, and it is not im- 

 probable that nearly at the termination of the north-east trade wind 

 a current joins with a similar current carried by the south-east trade 

 wind ; both uniting in forming the westerly current may thus cause 

 a greater assemblage of the various tropical molluscs and crustaceous 

 animals, a number of which possessing luminous properties may im- 

 part by their presence a higher degree of phosphorescence in that 

 particular portion of the ocean than is observed in other situations 

 except from similar causes. That the diffusion of the phosphoric 

 light possessed by these molluscs does not solely depend on the 

 creatures being disturbed (such as the passage of the ship through 

 the water, or other somewhat similar causes,) is evident, as a lumi- 

 nous mass may frequently be observed to gradually diffuse Its bril- 

 liant light, at some distance from the ship, without any apparent 

 disturbance ; and often during calm nights a similar glow of Ught is 

 diffused over the water, without there being any collision of the waves 

 to bring it forth ; and if a light breeze springs up during the same 

 night, the passage of the vessel leaves no brilliant trace in its wake, 

 although the same spontaneous diffusion of light is obser^'ed in the 

 water at some distance to be repeated as before ; the phosphoric 

 light being confined apparently solely to the occasional groups of 

 molluscs, which when we succeeded in capturing them in the towing 

 net, resembled for the most part pieces of crystal cut into various 

 fantastic forms, round, oval, hexagonal, heptagonal, &c. From the 

 bodies of these a faint or a bright light (according to the greater or 

 less duration of time the animal may have been removed from the 

 water, that is, we may say, by the intensity of its light we can 

 judge of its healthy or ^dgorous state,) would be seen to issue in mi- 

 nute dots from various parts ; and on the examination of both large 

 and small specimens, the large with the naked eye and the small 

 under a powerful lens, I could not detect any one peculiar secreting 

 organ for this luminous excretion. 



" It has often occurred during the voyage that the ocean became 

 suddenly brilliantly luminous, and at other times merely a constant 

 succession of scintillations were visible. Again, it was remarked 

 that no luminosity of the ocean was visible except what proceeded 

 from the wake of the ship, the other parts of the ocean exhibiting no 

 phosphorescence. 



" On the 15th of April, 1835, in lat. 8° 45' north, and longitude 

 21° 02' west, during the day large quantities of a beautiful pink 

 Medusa were taken in the towing net, which species I was pre- 

 viously aware possessed luminous powers, and as expected, at night 

 the ocean was brilliantly luminous, which luminosity continued until 

 about 8 P.M., after which time it had almost totally disappeared. 

 During the time the phosphorescence was visible, the Medusa before 

 mentioned was captured in large numbers, but on the disappearance 

 of the luminosity no more were caught, evidently showing that the 

 phosphorescence of the sea this evening was occasioned by their 

 presence. I have frequently remarked that when the ocean appears 

 brilliantly luminous, besides the animals producing the phosphores- 

 cence, several crustaceous animals and a number of small fish are 



