ON LUMINOUS ANIMALS. 5| 



common air; and that it is not sensibly diminished in 



hidrogengas. v : lU. 



I may farther add, that Spallanzani*s experimfenis of Sp^itanzanP.; 



diffusin«^ the luminous liquor of the medusain water, milk, experiments 



, , ^ . , . ,. ... p, . , against his 



and other fluids, arem direct contradutiou ot his own theory ; o^n theory. 



as is also the extinction of the light of these mixtures by 



the application of a hijjjh degree of heat. 



If the light emitted by animals were derived from their Their Upht not 

 food, or the air they respire, as supposed by Carradori, the ^^"7^^ ^i^""^ 

 phenomenon should be increased or diminished, according 

 Xo the quantity of food qr air, that the creatures consume ; 

 but we do not find this to be the case ; for in those situations 

 where they are sometimes found to be the most luminous, 

 they are deprived, in a great measure, of these assumed 

 sources of their light. 



[n fact, the luminous exhibitions of living animals are and indepen* 

 not only independent of all foreign light, but are frequently p^^^ foreign 

 deftroyed by the latter. I have always found the shining 

 of the medusai to cease upon the rising of the moon, or at 

 the approach of day ; and when out of the sea, I never 

 could excite them to throw out light, until they had been 

 ke[)t for some time in the dark; all the luminous insects 

 likewise secrete themselves as much as possible during the 

 day time, and go abroad only at night. I have, it is true, 

 found, that the scolopendra electrica will not shine, »nles«^ except perhap» 

 it has been previously exposed to solar light; but I have in the scoloi 

 observed, that it shone as brilliantly and as frequently, ^^" ^*' 

 after being kept a short time in a light situation, as when 

 left uncovered the whole day. The circumstance of the sco- 

 lopendra requirino exposure previous to its jrivincj out light This exception 



I n n I r » n » a curious fact. 



is very unaccountable ; as the insect, when left to itself, 



always seeks as much as possible concealment during the 

 day; indeed it is the opinion of some naturalifts, that it is 

 killed by the light of the sun. •" 



The opinions of Brugnatelli and Carradori are con- whether light 

 nected with some general doctrines, respecting the nature b*^ "^^^^"^l 

 of light, which { shall not at present venture to discuss. JJ^^^Jjj . 

 It appears to me, that the question is fttill unresolved, 

 whether light has a substantial existence, or is a pheno- 

 menon depending upon certain operations or conditions of 



K 2 the 



