A Solid HERMETICK PHOSPHORUS; a mixed Matter, which being exposed for about half a minute of an hour to the Sun, or only to Day-light, or to a bright Fire or Candle; will shine in the dark for some minutes. Made by Dr. Fr. Slare, and by him given to the Royal Society, Apr. 3. 1679. The first of this kind was made by Monsieur Baldwin, a German Lawyer who gave it the Name above, but with no direction for the making of it. Nor doth he so much as mention the Materials.

I call it Solid, to distinguish it from two Liquid kinds. The Author of one, supposed to be Mr. Dan. Krafft. The other invented by the Honourable Mr. Boyle; which He calls the Aerial Noctiluca; and whereof He hath lately published an excellent Discourse. In whose Laboratory, the solid kind was also made by his direction, several ways.

Of the Process for This here, Dr. Slare some years since received a hint from Dr. Christian Connerding, Archiater to the Duke of Zell. And not hearing of any one, amongst many that have try'd, besides these Three, to have succeeded in the making of it, he hath imparted the following Account.

Take good firm Chalk, ignite it in a Crucible, and then powder it. Put into a pint or half a pint of strong Spirit of Nitre, Cochleatim, as much hereof, as will serve well to satiate it, i. e. till it becomes sweetish, and makes no Effervescence upon the injection of the Chalk. Then dilute this Liquor with fair Water, filtre it through a Paper, and so evaporate it in a large Glass, or glazed Vessel, or good Hassian Crucible to a dry Salt. The preparation whereof may be perform'd in four hours: whereas I have seen a PocessProcess, that would take as many Weeks to follow it.

he main business lies in the good Enchiresis; about which these several Directions must be carefully observ'd.

First you must prepare a Vessel of Clay, somewhat like a shallow Coffee-Dish, of three, four, or five inches in Diametre, and an inch in depth, very well baked and neal'd. Then place it under a Muffle, after the manner of a Refining Furnace, in the place where the Cuppels usually stand: and so make it red hot. Then put the prepared Salt into it, by little and little, not above ʒj ss. or ʒij at a time. Keep the fire to that degree, which will suffice to make the Salt boil in the Dish, so as to spread it self every way, and creep up the sides of it. Before the Salt, last put in, be consumed, be sure always to be ready, to make a new addition, otherwise your labour so far is lost, and you must begin again. When five or six Drachms are fum'd away, take the Dish nimbly out of the fire, so soon as the Salt last put in is dry. If you have wrought well, what remains in the Dish will be yellowish in some parts, and every yellow part will shine. Secure this Matter from the Air by fitting and cementing a Glass to it: otherwise it will loose its property in one Week.

As to the Cause of this strange Phænomenon, Dr. Slare continues to this effect. I shall in short offer my Thoughts, and refer them to your Judgment. Two Questions may arise: What it is in this Mixture that yields the light? and, How it doth it? As to the first, I take it to be the pure fiery part of the Spirit of Nitre embraced by the Chalk. For that the rest is weak and phlegmatick; as appears, if it be distill'd. Also, that about the end of the Operation, a black Fume begins to rise and fly away. That if by continuing the Dish too long in the fire, you drive all the Nitrous parts away, the Chalk which stays behind will not be luminous. Or if the Matter duly prepar'd, be exposed to the Air, and thereby prey'd upon, the same effect will follow.

As to the Second, I suppose, That it shines not by Imbibition of Light, but by Impression from it, from whence proceeds a motion therein productive of Light. Which we may the rather be induced to believe, In that if it be put into an Iron Cover, and then an Iron Box, and a good heat given to it, it will shine so vigorously as to seem to kindle the Air about it. That two Men by following their blow close, will make a Bar of Iron glow, or shine in the dark. And although the Impulse of Light may seem small; yet upon Bodies nearly related to it, as This seems to be, it appears to be great. As in those odd effects it sometimes hath upon Infants unus'd to it; and People that have sore Eyes; or have been newly Couch'd; as it happen'd to Dr. Castle sometime since, who by making bold with his Eyes too early, (i. e. by a too frequent admission of light to them,) after that Operation, did thereupon suffer such extreme pains, and mischief in his Eyes, that he now dispairs of ever seeing more.

Mr. Haac (a) (a) Author of the Experiment upon the Loadstone, Part 3. saith he, hath frequently repeated the following Experiment upon this Phosphorus. If it be exposed to the Morning Light a little before Sun rising, it presents a bright Rosy hugh. As the Sun approaches the Meridian, it advances to a higher and more firey Complexion, like that of a red hot Iron. A little after Sun-set, declines to a pale wan colour, like Chalk, or rather Mother of Pearl.

Expos'd, saith he, to the light of a Candle, or flaming Fagot, it receives a pale Luminous colour, as from the Sun towards setting. But being expos'd for a considerable time to the most clear Moonshine that I have seen in London, I could not perceive it to become Luminous in the least.

It hath been kept, saith he, in the Vacuum of my Great and Noble Patron, the Honourable Mr. Boyle called Vacuum Boyleanum, and by his Highness Prince Rupert and Himself observ'd, for above four or five months, without any diminution of its shining property.

He adds, That he hath lately found a way to affix this Shining Matter to Glass, whereby some not unpleasing Experiments may be made. Thus far Dr. Slare.

As to his Ingenious Conjectures of the Subject and Cause of Light in this Phosphorus: because he hath desired my Opinion, I shall therefore subjoyn it in a few lines.

As to the first, What it is which gives the Light: It seems hard to say, Whether it be the Cretaceous Salt, the Nitrous Salt, or some Igneous Particles incorporated with them in the Operation? It is plain, That one way or other, they do all concur to produce it.

As to the Question, How these Particles give light? It should first be stated, What Light is; Whether it be a Body? Which, though much disputed, yet in strict speaking, is an absurd Question; all one, as to ask, Whether a Quality, be a Body? But the meaning of the Question is, or ought to be, Whether there be any Body in Nature, which is the peculiar subject of Light, or metonymically may be called Light? Or whether more Bodies than one, may successively be the immediate subject thereof? If so, Whether it be any other Adjunct besides Motion? If only Motion, Whether as there is one peculiar Motion, at least for a Musical sound, so another for Light? And in regard there are some Experiments which seem to favour each of these Questions: such an Answer should be given as will correspond with all those experiments; and will be too long to suit with this Catalogue.

I shall here only say, I am inclined to believe, That, in this Case, all the three Bodies above mention'd serve together to compose an Apt Recipient of that which is the true Luminous Body. That, as in the mixture of Sulphur and Water, sulphurious Salts, of affinity with both, are used as a medium: so here, the Cretaceous Parts serve to fix the Nitrous; and the Nitrous, to fix the Igneous; being of a middle nature and readily incorporated with them both. And being in this union exposed to the Sun Beams, or other Light, the Igneous parts serve, for some time, to retain a certain portion of such as are Luminous, or to give, as I may say, a degree of Fixation to These also: and that therefore this Mixture is kindled or made to shine, by puting it into the Light, as a stick is made to burn, by puting it into the fire.

Of shining Flesh, see a Relation of some Remarkable Circumstances, made by Dr. J. Beal, and published in the Phil. Trans. (a)(a) N. 125.