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hand they by no means prove that it is properly That variety of the blue fluor of Derbyfhireinherent in the phofphoric fubftance itfelf. which when fcraped or ftruck emits a fetid

The folar phofphori are not only capable of bituminous odour, is the' moft phofphorefcentbeing excited by the rays of the fun but by any by heat of all the known fubftances; it glowsother light that is fufficiently powerful, and when moderately heated with a pale emeraldthofe phofphorefcent fubftances which fhine green light fufEciently intenfe to be very vifiblewith the greateft brilliance by expofure to the even in day light, To the fecond rank belonglight of day, are, as might naturally be ex- the common Swineftone, the common bluepected, moft eafily excited by other luminous fluor, and red felfpar, all thefe as well as thebodies. The rays of the moon even when con- following exhibit a white or reddifh light. Thecentrated in a lens appear to be incapable of third clafs includes the diamond, the ruby,illuminating even the moft fenfible kinds of carbonated barytes, chalk, colourlefs calcareousphofphori. The light of a bright candle, or fpar, fea fhells, granite, and white fluor.the momentary flafh from the explofion of a The fourth clafs comprehends white fand, car-little gunpowder, or from an electrical dif- bonated magnefia, heavy fpar, flint, whitecharge, are fufficient to render Wilfon’s phof- marble, quartz, porcelain and earthen-ware,phorus, when well prepared, very vifibly lumi- The fifth clafs includes moft of the metals,nous. fulphat of potafh, borax, white paper, white

It is not very certainly known what is the linen, fawduft and afbeftos. Under the fixtheffeft of the different gaffes on the luminous and laft clafs are comprehended oil, wax,property of thefe bodies. According to fome fpermaceti and butter when boiling or nearly fo.obfervers, a piece of calcareous phofphorus, To exhibit the luminous property of thefe bodieswhen placed in the receiver of an air-pump, in the greateft perfection, the harder onesbecomes rapidly lefs luminous as the air is ex- thould be reduced to a very coarfe powder andhaufted, but according to others the rate at fprinkled in a dark room on the furface of awhich the light fades is not more rapid than thick metallic plate heated below rednefs. Aufual. We have the refpedtable authority of very ftriking exhibition of the phofphorefcenceMr. Canton, for ftating that his phofphorus in- of the fetid blue fluor may be made by heatingclofed in a glafs flalk, and hermetically fealed, fome oil in a clear flaik till it becomes luminous,retains its property of becoming luminous for and then dropping in about a teafpoonful ofat lead four years, without any apparent de- pulverized fluor: the inftant this, latter comescreafe of aClivity. in contaCt with the hot liquid a bright flaflr of

§. 2 . Phofphori from heat. green light is given out, which may be renewed

Befides thofe fubftances that are phofphoref- for many times by repeatedly fhaking the veffei.cent by expofure to the rays of the fun, there Moft of the above mentioned fubftances areare others which give out light when Amply phofphorefcent alfo by friction, which is af-heated. Thefe materially differ from the former cribed by Mr. Wedgewood to the heat producedin this circumftance, that after having been on this occafion; in fome inftances it may, yet ascontinued at any particular temperature till there are certain bodies, fuch as Tremolite andtheir luminoufnefs is exhaufted, they are inca- a particular variety of blende, which give outpable of becoming again luminous, except at a much light even from the fcratch of a pin, thegreater heat than that to which they were luminoufnefs in thefe cafes can hardly havefirft fubjedted. The range of temperature at been excited by the rea&ion of the triflingwhich thefe bodies become luminous is not very quantity of heat thus produced. Mr. Davy hasextenfive, commencing at about 400° Fahr. alfo obferved that if fluor be heated till it ceafedand terminating at the loweft vifible red heat, to become luminous, it is ftill capable of pro-In fome of thefe phofphori the light is almoft ducing light by collifion.momentary, but in others it endures many

minutes. The intenfity of the light appears to §. 3. Spontaneous Phofphori.

undergo no fort of alteration whether the body In this fe£tion we mean to include certainthat emits it is in a Torricellian vacuum, or animal and vegetable fubftances which at aplunged in any of the natural or artificial gaffes, particular period of their fpontaneous decompo-The following is a lift of the fubftances exhibit- fition become luminous. In animal fubftancesing this property, arranged by Mr. T. Wedge- this phofphorefcence makes its appearance be-wocd according to the brilliancy of their light.' fore the commencement of putrefaction, and

• Phil. Tranf, vol. Ixxxii, p. 1%