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ceafes when the latter is compleatly eftablifhed.The flefli of birds has we believe never exhibitedthis phenomenon, and that of quadrupeds butrarely. Several fpecies of infects are luminous,as the common glow worm, the fire flies ofAmerica, and the fulgora of China ; alfo a kindof crab, (the cancer fulgensj a few fhell fifh,and fome of the marine mollufcte: thefe how-ever are luminous not merely during the periodjuft mentioned, but alfo when alive. The flefliof a few frefh water fifh efpecially the carp, andof the tadpole, but not of the frog, becomesluminous before putrefaction. But the flefliof fait water fifh more than all other fubftancesis peculiarly rich in phofphorefcent matter, andaccordingly has been the principal fubftance onwhich the following experiments have beenmade. Of vegetable matters that become lu-minous the principal is decayed wood; peatalfo, though very rarely, hase xhibited a fimilarappearance. The chief obfervers who haveturned their attention to this fubjedt are Boyle,Canton, f and Dr. Hulme. g
The only laboratory required for thefe pro-ceffes jS a dark room, and the only preparationof the fifh is that they fhould be gutted andfplit, and their fcales taken off. The herringfeems to afford more light than other fifh.
The time which fea fifh, as frefh as they cancommonly be procured in a market, take tobecome luminous is about 12 hours or lefs: thephofphorefcence is faint and partial at firft, butfoon fpreads over the whole furface, and be-comes very bright before any putrefaction comeson; in proportion as this latter flate is eftablifh-ed the light becomes more faint, but does notentirely difappear in lefs than four or five days:the luminous matter may be fcraped off with ablunt knife, and will continue to fhine for aconfiderable time. But though the emisfion oflight diminifhes as putrefaftion increafes, thereappears no ncceflary connexion between thetwo procefles, for if a piece of herring is putinto a brine confifting of i part by weightcommon fait and 8 parts water, it will befound in about 24. hours that the liquor whenagitated is flightly luminous, and during thetwo fucceding days its brilliancy will increafe;then declining, it will become wholly extindtin three or four days more, and at the end oftills period both the flefli and brine will beentirely f ree f rom any putrid fmell. Thelu phats of foda or magnefia employed in thefame proportions as common fait will produce
1 Phil. Trans, lix. p 446.
fimilar effects, only the phofphorefcence willnot continue fo long.
The phofphorefcence is deftroyed by im-merfion in pure water, in lime-water, carbonatedwater, and liquid fulphuretted hydrogen, alfoby fermented liquors, by alcohol, by the mi-neral and vegetable acids, and by the alkalies,alfo by faturated folutions of tliofe neutral faltswhich when moderately diluted contribute molteminently to its prefervation. Hence if fomeof the luminous matter be fcraped from thefurface of the fifh, and well (haken in a dilutefolution of common fait, Glauber’s fait, &c.the whole will appear richly luminous,,but bythen adding a fufficiency of dry fait to faturatethe folution, the light will be extinguifhed: inthis cafe it is however only latent, for by pour-ing in pure water enough to reduce the llrengthof the faline folution, the light reappears asbefore, a fubfequent dofe of fait wall againextinguifh it, and more water will reftore itsluminoufnefs.
The production of this phofphoric light doesnot afford any heat afcertainable by the ther-mometer. By expofure to a freezing tempera-ture the light is rendered latent, but it is whollydeftroyed when plunged into boiling water; aconfiderable warmth however obvioufly increafesits brilliancy.
It appears that this light cannot be producedexcept by the contact of atmofpheric air, yetwhen once excited it is not ineveafed by beingplaced in oxygen gas, or impaired by azot*When put into the receiver of an air-pump itbecomes faint, and is at lerfgth extinguifhed asthe exhauftion of the vt-ffel proceeds; the re-admillion of air reftores its former brightnefs.Nitrous gas, carbonic acid, hydrogen, andfulphuretted'hydrogen totally and inftantaneous-ly extinguiih it.
The light of dead glow-worms, and of rottenwood follows nearly the fame rule with regardto the a£tio.n of temperature and the gaffes asfifh light does, but it feems to be little affected,by pure water and various faline folutions which-have fo ftriking an adtion on the latter.PHOSPHURET Y SeePHOSPHU RETTED V Phosphorus-HYDROGEN J (KuncMs.)
c Ditto, xc, p. 161. xci. p- 4 ° 3 -