An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. X. Of Glass.

I. What Ashes are most proper for the mak∣ing of Glass. THE most proper Ashes that are known, for the making of Glass, are those of the Herb Kali, and Fern.

Tho' the parts of Ashes be very gross and irre∣gular, and cannot, tho' they lean one upon ano∣ther, so unite together, as to compose a hard Body, because the Air which fills the Pores that are left between them, doth hinder their Rest; yet the Ashes of the Herb Kali and Fern, are therefore the most proper of all others for the making of Glass, because they abound with abundance of fixt Salts, which are very porous and spungy; so that when these Ashes are put into a violent Fire, their corners are consumed by it, and by this means the surface of their parts is made so smooth and even, that they touch in more Points than they did before, and afford a free passage to the Beams of Light, and cannot be rendred dark or opake without the mixture of some Forrein Matter.

II. Why Glass is Transpa∣rent. Glass notwithstanding that it is a hard Body, and made up of the thick and irregular Particles of A∣shes, yet doth constitute Transparent and Light∣some Body.

The cause of this perspicuity of Glass, may be easily gathered from the make of it. For whilst the matter of it, was by the violence of the Fire reduced to a liquid form, and all its Particles in agitation, the Fire flowing round about them, hol∣lowed many Cavities in them, which the 2d Ele∣ment freely entring, diffused the action of Light to all parts, in right Line••. And forasmuch as the said Pords, are after the Glass is made 〈◊◊〉〈◊◊〉 preserved and kept open, by th•• i••cessan•• passage of the subtil matter, and are filled as be∣fore, they cannot but transmit the L••ght as fore∣merly, so that the same transparency which was in the molten and liquid Glass, remains in the cold and hardned. For this i•• a thing common to all Bodies that are melted in the Fired that whilst they are yet in that liquid form their parts do easily accommodate themselves to any Figure, which they retain after that they are grown cold▪ If at any time any darkness be perceived in Gl••ss, that proceeds from some Dr••g•••• Clouds or Bubbles that are mingled in its texture, which since they are much more numerous in thick Glass than 〈◊〉〈◊〉 thin, therefore we must inpute the darkness of thick Glass to them.

III Why Glass is Brittle. Glass is very Brittle, and will not suffer it self to be extended, but upon the least stroak breaks to shivers,

The Reason is, because tho' Glass be a hard Body, and does consist of parts that are thick e∣nough, yet forasmuch as the surfaces by which they touch one another, are very small, so that they joyn only in Points, for this reason it ••s, that if they be never so little separated from each other, they lose their union and fly into bits. Whereas many soft Bodies are much harder to be broken, because they have their parts so intangled, that they cannot be separated, without the breaking of many of those Branches, by which they were held together.

IV. Glass some∣times breaks of it self. It is a thing known by long experience, that Glasses after they have lasted a long time, do at last break of themselves. More particularly this is notorious to them, who grind those Glasses that are used in Prospective Glasses; for they find that after they have been polished a long time, they slit of themselves. The cause whereof is, because the Saline Particles, being agitated by the subtil Matter, do endeavour to break loose: As may be gathered from hence, that in the Winter season, and Rainy weather, something may be wiped from Glasses, that hath a Saltish taste. And not long since there was a certain man at Amsterdam, who broke Rhenish-wine Glasses only with his Voice, and that not very strong neither, but tuned to a certain Pitch.

V. Why Glass that is newly taken out of the Furnace doth break when ex∣posed to the Air. A Glass newly taken out of the Furnace, if it be exposed to the cold Air breaks immediately; and so likewise if any water be cast upon it.

The Reason is, because when the cold doth draw together and narrow the Pores of the Glass, the subtil Matter and the fiery Particle•• are by this means lockt up in them: And whilst the former of these press to make their way through the Pores of the Glass, and the others endeavour to get out from it, they by striving to widen the Pores, make the Glass to fly in pieces.

VI. A cold Glass ••eld to ne•••• the Fire cracks If a cold Glass be held so near to the Fire, that it heat in one part more than in another, it present∣ly breaks.

The Reason is, because when the Fire is got in to the Glass, the Pores of it are not all equally dilated by it, and therefore when the subtil matter gets into them, seeing the Pores where the Glass is cold, are not wide enough for its free passage, it makes way for it self by rending the Glass to

pi••ce••▪ But if it be by degrees, and by little and little held b•• the fire▪ it will suffer no hurt at all; b••cause all 〈◊〉〈◊〉 po••••s will by this means be suffici∣en••ly 〈◊〉〈◊〉 so as to afford a free and open passage for the subtil matter. And therefore when Glas∣ses that have contained any hot Liquor, are suddain∣ly ••mptied and exposed to the Air, they crack immediately; because the subtil matter, which is pent up in the pores of Glass Vessels, striving to get out, finds no way for it self, because the pores are constringed by the coldness of the Air; and therefore makes its way by breaking the 〈◊〉〈◊〉 sides of the Glass.

VII. How the breaking of Glasses may be prevent∣ed. To avoid this breaking of Glasses, they that belong to the Glass houses▪ take the Glasses that are newly blown, and set them in a place at some distance from the fire to Neal, as they call it, removing them every 6 hours, the distance of 8 or 10 Foot, before they expose them to the Air; by which means all the parts of the Glass being insensibly and equally cool'd, there is an equal constriction of the Pores, so as that the sub∣til matter which can pass one of them, can with like ease pass all the rest.

VIII. How Glass comes to have an Attractive Virtue. Glass seems to have something of a Magnetick Virtue; for when it is strongly rubb'd, so as to be heated thereby, it draws the neighbouring Bodies to it self.

The Reason is, because the agitated particles of the 1st Element, continually pass from the Glass into the Air, and others from the Air return to the Glass, to take up the room of the former; and because those particles which return from the Air, have not all of them the same degree of Agitation, those which have less, are driven towards the little slits; which have no correspondent Pores in the Air, and being, as it were, heaped upon one ano∣ther, do constitute certain wreaths, which in pro∣cess of time acquire determinate Figures, which afterwards are not easily changed. Wherefore when Glass is strongly rubb'd, so as to grow hot, these wreathed particles being driven out, are dif∣fused indeed through the neighbouring Air, and enter into the pores of Bodies that are about them: But forasmuch as they do not there find an open and ready way for themselves, they return to the Glass immediately, and carry along with them any little Bodies they meet with in their way.

IX. Glass be∣comes va∣riously co∣loured, by being ming∣led with Metals. When in the melting of Glass, a Metal is mix'd with it, the parts whereof cannot so easily be smoothed and polished by the action of the Fire, as those of the Ashes are whereof the Glass is made, then the Glass becomes ting'd of divers Colours.

The Reason is, because the metalline particles, which are very irregular, do insinuate themselves into the pores of the Glass; and by this means, make the parts of the 2d Element, that pass through the same, to move and roll differently from what they did before, and consequently to represent those Colours which are caused by these their diffe∣rent rolings.

X. What is the reason of the stif∣ness of Glass. Glass is very stiff, and cannot be bent without the danger of Breaking. Wherefore, if it be ne∣ver so little bended one way, it presently springs back like a Bow, and returns to its former Figure.

The Reason is, because this bending doth some¦what change the figure of the Glass, and straitens the pores of it; so that the particles of the 1st E∣lement, that before past through them, finding then way not so easie as before, and yet pursuing their motion as far as they are able, force the sides of them, and endeavour to reduce them to their former figure. For this property of leaping back, is not peculiar to Glass only, but to all hard Bodies, whose particles are joined by immediate contact, and not by the weaving or intangling of Branchy parts. As is evident in a bended Bow of Steel or Wood, which presently leaps back to its former state, except it have continued bent too long▪ and that the subtil matter hath found or made it self other passages to run through▪

XI. Why Glass melts by the force of Fire. Glass is melted by the action of fire, and whilst 〈…〉〈…〉 so, is easily formed into all sorts of figures.

The Reason is, because the parts of Glass having been before worn and polished by the force of fire, are easily moved, and obliquely creeping, and flowing one upon another, they begin to touch each other in some small part of their surfaces, and following one another, constitute a fluid Body, which may be formed into any figures, according to the pleasure of the Artist. Moreover this fluid Body, as it grows Cold, becomes tough like Bird∣lime, so as that it may be drawn into thin Threds; because as long as that motion is continued in it, whereby its parts do flow; lying obliquely upon one another, it may the more easily be drawn out into Threds, than it can be broken.

XII. Glass bea∣ten to Pow∣der becomes a Poison. Glass beaten into Powder, according to the opi∣nion of some Physicians, becomes Poison.

The Reason of this, as I suppose, may be, be∣cause the pieces of Glass are hard and sharp, which hurting and wounding the Membrans of the Sto∣mach and Guts, as well as of the other smaller vessels, become destructive to the Body of Man. For I do take Glass, when it is yet whole, to be no Poison at all; forasmuch as many have swal∣lowed it without any hurt; which is an argument, that all the hurt that can accrue to our Bodies from Glass, must proceed from the hardness and figure of its little particles.