38 MEMOIR III. 



as they pass the sides of the vessel, or follow in the track ; 

 the kind of light exhibited by this variety, is perhaps more 

 brilliant and condensed than that of any of the others, and 

 very much resembles every way, that of the red, gold, 

 and silver rain of the Pyrotechnist. 



(B.) The former kind of luminosity, is not unfrequently 

 accompanied by flashes of a paler light of momentary dura- 

 tion, and independent of the light with which these strike the 

 visual organs, often illuminate the water to the extent of 

 several feet ; these are more or less vivid, according to the 

 distance of the observer, and the depth at which they make 

 their appearance. This kind of luminosity, resembles 

 extremely the lightning so often seen in tropical regions, 

 and which presents itself in diffused flashes of light, now 

 issuing from one mass of clouds, now from another, in 

 constant succession over tlie whole face of the heavens. 



These modifications of the luminosity of the ocean, are 

 common to every part of it in the more temperate and 

 tropical regions. A variety of the last kind, (B) in which 

 these larger masses of phosphoric light possess a greater 

 degree of permanence, has been noticed by Spallanzani in 

 the Mediterranean, and may occur in other situations, but 

 has nev^cr been seen by the author. " If" says he " in the 

 beginning of the night we enter the strait of Messina 

 (October Avas the month in which these observations were 

 made) in a low bark or boat coasting near tlie land, 

 where tlie water is perfectly calm, the Medusae, which are 

 usually very numerous there, begin to shine with a light, 

 which as the darkness increases, acquires intensity and 

 extent, every medusa resembling a bright torch, that may 

 be seen for some hundred paces around ; and on approach- 

 ing it, the brilliant phosphorus shews the form of the body. 

 This light, when the evening twilight is extinct, is of a lively 

 white, which strikes the eye even when the animal is five- 

 and-thirty feet below the surface. As the medusa, by i(s 

 oscillation, transfers itself from place to place, so the light 



