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The laft perion who has paid much attentionto the fnbjeft of folar phofpliori is Mr. B.Wilfon, by whofe very able experiments fomeimportant errors of Becaria have been re£tifiedand to whom die difeovery is due of the fim-pleft and mod powerful of all the phofplioribelonging to this clafs. Wilfon's phofphorus isthus prepared. c Selett a fcore of oyller (hells,the thicker they are the better, then take mo ftof the flaming coals, but not all of them, off afire that is burning brifkly, drew the (hells overthe furface and replace the coals that have beentaken off. In about an hour’s time take outthe calcined (hells obferving to break them aslittle as poffible, and after expofing them for afew minutes to the light they will be found tohave acquired a high degree of phofphorefcenceglowing in the dark in a very beautiful manner,with molt of the prifmatic colours. It is nothowever abfolutely neceffary that the (hells(hould be calcined in the open fire, for if theyare heated fufficiently in a clofe crucible theywill exhibit prifmatic colours, chiefly blue andgreen, though not fo bright as by the formermethod. If the calcination is effected in aniron crucible, all thofe parts of the (hells thatare in contact with the Tides of the cruciblewill glow with a red light. The contact ofinflammable matter, and particularly charcoal,with the (hells during their calcination appearseminently to contribute to the brilliancy of thephofphorus; hence it is that if the (hells arecalcined in a crucible in contadf with thin platesof fteel, the phofphorus thus produced will bemuch more bright and of more various coloursthan where plates of iron are employed; andon the other hand if flat pieces of charcoal aremade ufe of, the intenfity of the colours, efpe-ciaily the blue, green, and red, is far greaterthan in thofe produced by the fteel.

In conducting experiments on folar phof-phori, as the light from many of them is veryevanefeent, fome contrivance is neceffary thatthey may be prefented to the eye immediatelyon their removal into the dark, all other lightbeing at the fame time carefully excluded. Forthis purpofe it is convenient to have a fnrallclofet painted black on the infide, and with ablack curtain hung up before the door; thewindow of the clofet (hould be accuratelyclofed with a wooden (flutter fined with blackcloth and a thick curtain of the fame colour.In the (flutter (hould be a fmall Aider throughwhich a perfon within the clofet may expofeany i'ubltance to the fight, at the fame time that

* WilfQn on P

the interpofed curtain prevents any external raysfrom reaching the eyes of the experimenter, bywhich even the weakeft degree of phofphorei-cence will fcarcely efcape his obfervation.Laftly, to provide for a due fupply of frefti air,two pieces of curved pipe made of any opakematerial (hould be fixed in the door, the one atthe top and the other near the bottom. In aroom thus conftrufted the following appear-ances may be perceived.

Any of the phofpliori mentioned above, af-ter expofure to the light for half a minute orlefs, being introduced into the clofet, will beobferved to emit light for a longer or (hortertime, becoming by degrees more and more dimtill their luminoufnefs entirely ceafes. To pro-duce this quality in fome the dire£t rays of thefun are neceffary, but in others, particularlythe calcareous and barytic phofphori, the com-mon light of day is quite fufficient; in all how-ever the light is greater when the weather isdry and warm, than when it is cold and wet.The colour of the light in mod cafes is whiteor reddilh white, but in Wilfon’s phofphorusnot only white but all the prifmatic coloursmake their appearance, fometimes being allunited in a (ingle fpecimen, at other times eachpiece exhibiting only one or two colours. Inevery fpecies of folar phofphorus the light afterhaving been extinguithed may be renewed forany number of times without the fmalleft appa-rent diminution of brilliancy by finvple re-ex-pofure for a few feconds to the light.

If while the phofphorus is prefented to thefight it is moderately heated, its luminoufnefswill by this means be very fenfibly augmented.Thus if a common box fmoothing iron heatedin the ufual manner be placed for half a minuteon a (heet of dry white paper, and the paper bethen expofed to the light, and afterwards exa-mined in the dark clofet, it will be found thatthe whole paper will be luminous, that parthowever on which the iron had (food beingmuch more finning than the reft.

The effects of a variation in temperature onphofphori after having been expofed to thelight are alfo very remarkable. It a thin glafstube be filled with Canton’s or Wilfon’s phof-phorus, and, as foon as it is brought into thedark clofet, be plunged half way into a freez-ing mixture for a few minutes, it will be foundon again withdrawing the tube that the coldportion is much lefs luminous than the other,and if the freezing mixture has been fufficientlypowerful, it will be entirely extinguiftied. Thiftlofphori, p. ao.