464 THE AQUARIAN NATURALIST. 



guishable, even in a small vessel of the most limpid 



water : 



. . . . " the fibrous cloud, 



That catches but the faintest tinge of even, 

 And which the straining eye can hardly seize, 

 When melting into eastern twilight's shadow, 

 Is scarce so thin, so slight." 



They are, nevertheless, exceedingly beautiful objects, 

 and, in a favourable light, splendidly iridescent : 



"Mille trahens varies adverso sole colores." 



Their hues of rainbow-light glow like the gleams of 

 an air-bubble in the sunshine, presenting tints which 

 scarcely find comparison on earth; and during the 

 night, many of them are, under certain circumstances, 

 brilliantly phosphoric ; nevertheless, they appear to 

 emit their phosphorescent flame only when the water 

 is agitated, or when they come in contact with op- 

 posing bodies. In his observations on one of these 

 creatures, Mr. Beaufort says, " On holding a Salpa in 

 my hand, and gently pressing it, a faint flame seemed 

 to pervade the whole inside, and on each projecting 

 point there seemed to stand a little globule of very 

 vivid light. On increasing the pressure, its brilliancy 

 likewise increased for a few moments, then gradually 

 declined for some time, as if exhausted by the exertion. 

 It may have been fancy, but at the time I was con- 

 vinced that it gave out a sensible degree of warmth 

 to the hand." The latter observation, says Dr. John- 

 ston, is probably not fanciful, but real ; for Humboldt 

 has proved that the Salpae, as well as the Pyrosomes, 

 when preserved in a bottle, make the temperature of 

 the water rise nearly one Centigrade degree. 



