250 VIEWS, &C. PHYSIOGNOMY OF PLANTS. 



substance the slightest vibrations of the tin were sufficient to 

 cause the animal to emit light. How do the blow and the vibra- 

 tions here act? Is the temperature momentarily augmented, 

 or are new surfaces presented? or, again, does some gaseous 

 matter such as phosphuretted hydrogen, exude in consequence 

 of this impulse, and burn when it comes in contact with the 

 oxygen of the atmosphere, or with that dissolved in the sea- 

 water, and by which the respiration of the Mollusca is main- 

 tained? This light-exciting effect of the blow is most remark- 

 able in a cross or sugar-loaf sea, (mer clapoteuse^] where the 

 waves, clashing from opposite directions, rise in a conical form. 



I have seen the ocean, in the tropics, luminous in the most 

 opposite kinds of weather, but most strongly so before a 

 storm, or in a sultry and hazy atmosphere with thick clouds. 

 Heat and cold appear to exercise but little influence on this 

 phenomenon, for, on the Bank of Newfoundland, the phos- 

 phorescence is frequently very brilliant in the severest 

 winter. Occasionally, too, the sea will be highly luminous 

 one night, and not at all so on the following, notwithstanding 

 an apparent identity of external conditions. Does the atmo- 

 sphere favour this development of light? or do all the dif- 

 ferences observed during this phenomenon depend on the 

 accidental circumstance of the sea being more or less impreg- 

 nated, in some parts, with the gelatinous portions of mol- 

 lusca? Perhaps these phosphorescent social animalcules only 

 rise to the surface under certain conditions of the atmosphere. 

 It has been asked, why our fresh- water swamps which are 

 filled with polyps are not phosphorescent. It would appear 

 that, both in animals and plants, a peculiar mixture of 

 organic particles favours this development of light ; thus, for 

 instance, the wood of the willow is more frequently found to 

 be luminous than that of the oak. In England, salt-water 

 has been rendered luminous by mixing herring-brine with 

 it ; indeed, it will be easy for any one to convince himself by 

 galvanic experiments, that the luminosity of living animals 

 depends on nervous irritation. I have observed strong phos- 

 phorescence emitted from a dying Elater noctilucus, on touch- 

 ing the ganglion of its fore leg with zinc and silver. MedusaD 

 also occasionally emit a stronger light at the moment the 

 galvanic circuit is completed/* 



* Humboldt, jRelat. hist., t. i. pp. 79, 533. Respecting the wonder- 



