NATURAL HISTORY. 



647 



food or air that the creatures con- 

 sume ; but we do not find this to 

 be the case ; for in those situa- 

 tions where they are sometimes 

 found to be most luminous, they 

 are deprived, in a great measure, 

 of these assumed sources of their 

 light. 



In fact, the luminous exhibi- 

 tions of living animals are not 

 only independent of all foreign 

 light, but are frequently destroyed 

 by the latter. I have always found 

 the shining of the medusae 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 kept for some 

 time in the dark ; all the lumin- 

 ous insects likewise secrete them- 

 selves 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 unless it has been pre- 

 viously exposed to solar light; but 

 I have 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 scolopendra requiring ex- 

 . posure previous to its giving out 

 light, is very unaccountable, as 

 the insect, when left to itself, al- 

 ways seeks as much as possible 

 concealment during the day ; in- 

 deed it is the opinion of some na- 

 turalists that it is killed by the light 

 of the sun. 



The opinions of Brugnatelli and 

 Carradori are connected with some 

 general doctrines, respecting the 

 nature of light, which I shall not 

 at present venture to discuss. It 

 appears to me, that the question 



is still unresolved, whether light 

 has a substantial existence, or is a 

 phaenomenon depending upon cer- 

 tain operations or conditions of 

 the ordinary forms of matter. But 

 the highly ingenious researches of 

 count Rumford, on the laws of 

 what have been called subtile 

 fluids, and the extraordinary ad- 

 vances lately made by Mr. Davy, 

 on the decomposition of substances 

 that were hitherto looked upon as 

 elementary, give us reason to hope 

 that future investigations may un- 

 fold views of the material world, 

 of which we can at present have 

 only an indistinct conception ; that 

 new modes of analysis may enable 

 us to see things, not "through a 

 glass darklj'," but more nearly as 

 thev are ; and that the boundaries 

 of physical and metaphysical sci- 

 ence, now so far asunder, may be 

 made to approach each other. 



Inthe presentstateof our know- 

 ledge, our business should be to 

 collect, arrange, and compare phae- 

 nomena, rather than to speculate 

 upon their nature. Nevertheless, 

 I cannot refrain from observing, 

 that the circumstances attending 

 the luminous appearance of living 

 animals, are much more favour- 

 able to the supposition of light 

 being a property than a substance. 

 The quantity of light emitted by 

 an animal in a ceitain time (ad- 

 mitting it to be matter), far ex- 

 ceeds that which could be possibly 

 supplied by the sources from 

 whence it is usually supposed to 

 be derived. Thus the luminous 

 appearance of some medusae may 

 be continued with the intermis- 

 sion of short intervals for an in- 

 definite time, notwithstanding the 

 creature be kept in darkness, and 



