73 



quarter of an hour, half an hour, or more, and at 

 others is suddenly extinguished, and does not appear 

 for some time." * " These luminous medusae are called 

 at Messina, bromi; and in the Lipari Islands, candel- 

 lieri di mare." A third kind of phosphorescency is 

 peculiar to gulfs, bays, and shores, and is very easily 

 excited, by any thing in fact which stirs the water, 

 since the mere movement of a fish is sufficient to ex- 

 cite a gleam. In this case it resembles a sea of milk, 

 of a pale diffused light, as when phosphorized alcohol 

 is poured on the surface of cold water. The first and 

 last of these phenomena appear ascribable to the 

 presence of minute crustacce or mollusca. The inter- 

 mediate variety seems to be the effect of larger 

 medusas, and of these only two have been discovered, 

 the medusa pellucens and m. spallanzani. The last 

 description of luminosity is comparatively rare, and 

 the appearance, described by Mr. Thompson, wit- 

 nessed in the bay of Gibraltar, was, as if " passing 

 through a sea of melted silver ;" this phenomenon 

 was occasioned by numerous luminous points, less 

 than the smallest pin's head, of the softest and most 

 destructible tenderness : closely inspected, they ap- 

 peared like hemispherical masses of a colourless jelly, 

 and are supposed, with much probability, to have been 

 some species of small medusae. 



The cancer fulgens\ of Sir Joseph Banks (noctiluca 

 Banksii of Mr. Thompson), or luminous shrimp, is found 

 towards Rio Janeiro, (between lat. 5 25' S., and 29 

 30' N., and West long. 17 18', and 32 55', they were 

 found abundant ; and it is evident their geographical 

 range is considerable. " The motions of the animal 

 were lively, and it gave out brilliant scintillations 



* Travels, vol. iv. p. 229. f See Plate, fig. 5. 



