330 On the Luminottsness of' the Ocean. 



of Good Hope. The luminousness of sea water is sometimes 

 occasioned by these living lanterns. I say sometimes ; for, in 

 most cases, notwithstanding the use of magnifying glasses, no 

 animal is perceived in luminous water ; and yet, whenever the 

 wave happens to strike a hard body and breaks, producing foam, 

 and whenever the water is strongly agitated, a light is produced 

 resembhng a flash of lightning. This phenomenon probably 

 originates from the decomposed fibrils of dead mollusca which 

 exist in infinite quantity in the depths of the sea. When this 

 luminous water is passed through a piece of dense cloth, these 

 fibrils are sometimes detached from it under the form of lumi- 

 nous points. When we bathed in the evening in the Gulf of 

 Cariaco, near Cumana, some parts of our bodies remained lumi- 

 nous on coming out of the water. The luminous fibres stuck to 

 the skin. From the immense quantity of mollusca dispersed 

 through all the seas of the torrid zone, it need not be surprising 

 that the water of the sea is luminous, even when no organic 

 matter can be separated from it. The infinite division of all the 

 dead bodies of dagyses * and medusae may render the entire sea 

 capable of being considered as a gelatinous fluid, and which is in 

 consequence luminous, has a nauseous taste, cannot be drunk by 

 man, but affords nourishment to many fishes. If a board be 

 rubbed with a part of the body of the Medusa hysocella, the 

 place rubbed becomes luminous whenever the finger, well dried, 

 is passed over it. During my passage to South America, I 

 sometimes put a medusa on a tin plate. If I struck the plate 

 with another metal, the smallest vibrations of the tin were suf- 

 ficient to make the animal shine. How did the blow and the 

 vibration act in this case .? Was the temperature instantaneous- 

 ly raised .'' Were new surfaces uncovered, or did the blow 

 make the phosphuretted hydrogen gas escape, so that, coming 

 into contact with the oxygen of the atmosphere, or with the wa- 

 ter of the sea, it produced combustion ? This effect of the blow 

 which excites the hght is particularly striking in a jumbling sea, 

 when the waves dash against each other in all directions. Be- 

 tween the tropics, I have seen the sea luminous at all tempera- 

 tures ; but it was more so before storms, or when the sky was 



• The genus Dagysa belyiigs to the Salpa tribe of Cuvier. 



