678 LIGHT. 
when viewed by the light of a candle, feemed covered 
with a greafy fcum. The third night, the light of the 
fea-vvater, while at reft, was very little, if at all, lefs than 
before ; but, when ftirred, its light was fo great as to dis¬ 
cover the time by a watch ; and the filh in it appeared as 
a dark fubftance. After this, its light was evidently de- 
creafmg, but was not quite gone before the feventh night. 
The frelh water and the filh in it were perfectly dark 
during the whole time. The thermometer was generally 
above 6o°. 
The preceding experiments were made with fea-water; 
but he now made ufe of other water, into which he put 
common or fea fait, till he found, by an hydrometer, that 
it was of the fame fpecific gravity with the fea-water ; and, 
at the fame time, in another gallon of water, he diffolved 
two pounds of fait: and into each of thefe waters he put 
a fmall frelh herring. The next evening the whole fur- 
faceof the artificial lea-water was luminous without being 
ftirred ; but gave much more light when it was difturbed. 
It appeared exaflly like the real fea-water in the preced¬ 
ing experiment ; its light laded about the fame time, and 
went oft' in the fame manner ; while the other water, 
which was almolt as fait as it could be made, never gave 
any light. The herring which was taken out of it the 
feventh night, and w'alhed from its fait, was found firm 
and fweet; but the other herring was very foft and pu¬ 
trid, much more fo than that which had been kept as 
long in frelh water. If a herring, in warm weather, be put 
into ten gallons of artificial fea-vvater, inftead of one, the 
water, he fays, will Hill become luminous, but its light 
will not be fo ftrong. 
It appeared by lome of the firft obfervations on this 
fubjeeft, that heat extiqguifhes the light of putrefeent fub- 
ftances. Mr. Canton alfo attended to this circumftance ; 
and obferves, that, though the greatell fummer-heat is 
well-known to promote putrefaftion, yet twenty degrees 
more than that of the human blood leems to hinder it. 
For, putting a fmall piece of a luminous fiih into a thin 
glafs ball, he found, that water of the heat of 118 de¬ 
grees would extinguilh its light in lefs than half a mi¬ 
nute 5 but that, on taking it out of the water, it would 
begin to recover its light in about ten feconds; but it 
was never afterwards fo bright as before. 
Mr. Canton made the fame obfervation that Mr. Ant. 
Martin had done, viz. that feveral kinds of river-fifh could 
not be made to give light in the lame circumltances in 
which any fea-filh became luminous. He fays, however, 
that a piece of carp made the water very luminous, though 
the outfide, or fcaly part of it, did not Ihine at all. For 
the lake of thofe perfons who may choofe to repeat his 
experiments, he obferves, that artificial fea-water may be 
made without the ufe of an hydrometer, by the propor¬ 
tion of four ounces avoirdupois of lak to (even pints of 
water, wine meafure. 
From undoubted obfervations, however, it appears, that 
in many places of the ocean it is covered with luminous 
infedts to a very confiderable extent. M. Dagelet, a 
French aftronomer who returned from the Terra Aultralis 
in the year 1774, brought with him feveral kinds of 
worms which Ihine in water when it is fet in motion ; and 
M. Rigaud, in a paper inferted (if we are not miftaken) 
in the Journal des S$avans for the month of March 1770, 
affirms, that the luminous furface of the fea, from the 
port of Breft to the Antilles, contains an immenfe quan¬ 
tity of little round lhining polypufes of about a quarter 
of a line in diameter. Other learned men, who acknow¬ 
ledge the exiftence of thefe luminous animals, cannot, 
however, be perfuaded to confider them as the caufe of 
all that light and fcintillation that appear on the furface 
of the ocean ; they think that fome fubftance of the phof- 
phortis kind, arifing from putrefaction, muft be admitted 
as one of the canfes of this phenomenon. M. Godehotie 
has publifhed curious obfervations on a kind of filh called 
in French honite, already-mentioned ; and though he has 
obferved, and accurately clefcribed, feveral of the lumi¬ 
nous infefts that are found in fea-water, he is neverthe- 
lefs of opinion, that the fcintillation and flaming light 
of the fea proceed from the oily and greafy fubltanceu 
with which it is impregnated. 
The abbe Nollet was long of opinion, that the light of 
the fea proceeded from electricity; though he afterwards 
feemed inclined to think, that this phenomenon was 
caufed by fmall animals, either by their luminous afpeff, 
or at leaft by forne liquor or effluvia which they emitted. 
He did not, however, exclude other caufes ; among thefe, 
the fpawn or fry cf filh deferves to be noticed. M. Da¬ 
gelet, failing into the bay of Antongil, in the illand of 
Madagafcar, obferved a prodigious quantity of fry which 
covered the furface of the fea above a mile in length, and 
which he at firft took for banks of fand on account of 
their colour ; they exhaled a difagreeable odour, and the 
fea had appeared with uncommon fplendour fome days 
before. The fame accurate obferver, perceiving the fea 
remarkably luminous in the road of the Cape of Good 
Hope during a perfeft calm, remarked, that the oars of 
the canoes produced a whitilh and pearly kind of luftre ; 
when he took in his hand the water which contained this 
phofphorus, he difeerned in it, for fome minutes, globules 
of light as large as the heads of pins. When, he preffed 
thefe globules, they appeared to his touch like a foft and 
thin pulp; and fome days after the fea was covered near 
the coafts with whole banks of thefe little filh in innu¬ 
merable multitudes. 
To putrefaction, alfo, fome are willing to attribute that 
luminous appearance which goes by the name of ignis 
fatuus, to which the credulous vulgar aferibe very extra¬ 
ordinary and efpecially mifehievous powers. It is moll 
frequently obferved in boggy places, and near rivers, 
though fometimes alfo in dry places. By its appearance 
benighted travellers are faid to have been fometimes milled 
into marlhy places, taking the light which they law be¬ 
fore them for a candle at a diltance ; from which feeming- 
ly mifehievous property it has been thought by the vul¬ 
gar to be a fpirit of a malignant nature, and been named 
accordingly Will with a wfp , or Jack with a lantk'orn ; for 
the fame reafon alfo it probably had its Latin name Ignis 
Fatuus. See vol. x. p. 830. 
A light in fome refpefls fimilar to thofe above men¬ 
tioned has been found to proceed from that celebrated 
chemical prodtnftion called phofphorus, which always tends 
to decompofe itfelf, fo as to take fire by the accefs of air 
only. Phofphorus, therefore, when it emits light, is pro¬ 
perly a body ignited ; though when a very fmall quantity 
of it is ufed, as what is left after drawing it over paper, 
or what may be dilfolved in elfential oil, the heat is not 
fenfible. But perhaps the matter which emits the light 
in what vve call putrefeent fubjlances may be fimilar to it, 
though it be generated by a different procefs, and burn 
with a lefs degree of heat. Putrefcence is certainly not 
neceffary to the light of glow-worms ; and yet their light 
is fufficiently fimilar to that of finning wood or flefh. 
Eleiflric light is unqueftionably fimilar to that of phof¬ 
phorus, though the fource of it is apparently very dif¬ 
ferent. See Chemistry, vol. iv. p. 201, 202. 
M. Deflaignes (Report of the National Inftitute for 
1810) defines pholphorefcence to be the appearance of a 
durable or tranfient light, unattended with fenfible heat, 
and not followed by any alteration "in inorganic bodies. 
This phofphorefcence prefents itfelf under different forms, 
and like folar light is decompofed by the prifm. From 
fome bodies it feems to emanate flowly and regularly, in 
others by fcintillation. Its colour is blue, but appears 
tarnifhed in thofe bodies which contain iron ; it may, 
however, be rendered clear, by feparating the metal from 
the bodies which contain it. In general, it has appeared 
to M. Deflaignes, that thofe bodies are the molt phofpho- 
refcent that contain in their compofition principles which 
can pafs from a ftate of gas, or liquid, to a folid form. 
All bodies give out light by conipreifion, whether they 
arc fluid, folid, or gafeous. He has alfo difeovered that 
1 points 
