Book XVII, chapters 5–10: Burning-glasses and wonderful sights

CHAP. V.

Of the mixt operations of the plain Concave-Glasses.

I Shall set down the mixt operations and benefits of both these Glasses, that what one cannot do alone, it may do by the help of another. If we would

Kindle fire afar off with a plain and a Concave-Glass.

It falls out sometimes that one shut up in prison needs fire, and the Sun beams shine not in: or else I will shew how we may kindle Gun-powder without fire, or make mines and fill them with Gun-powder, to blow up Castles or Rocks afar off without danger, setting them on fire by a plain Glass. A plain Glass as it receives the parallel beams of the Sun, it so reflects them, and therefore will cast the beams that are equidistant, a great way: but if a Concave-Glass receive them, it so unites them, that it sets things on fire. Wherefore, first proving where the Concave-Glass must be placed, that it may fire the fuel cast in: the next day, at the hour appointed, let the plain Glass cast in the beams upon the Concave-glass, that will unite them: so without danger, or any suspicion of the enemy, we may kindle fire for our use. Nor is it useless,

That by a plain and Concave-Glass the smallest letter shall appear very great,

when letters are so small that they can onely be seen: For I have seen St. Johns Gospel, In the beginning, &c. writ so small, in so little place, that it was no bigger than a small pimple, or the sight in a Cocks eye. By this Artifice we may make them seem greater, and read them with ease. Put a Concave-glass, with the back of it to your brest; over against it in the point of burning, set the writing: behind set a plain Glass, that you may see it: Then in the plain Glass will the Images of the Characters be reflected, that are in the Concave-glass, which the Concave-Glass hath made greater, that you may read them without difficulty. You may

With a plain and Concave-Glass, make an Image be seen hanging altogether in the Air.

Do thus. I said that by help of a Concave-Glass, an Image may be sent forth: and this is seen by none but those that stand over against it; Set the Concave-Glass to your brest, without the Centre place a Poniard against it, and going farther off, set a plain Glass against it; and looking in that, you shall see the Image reflected from the Concave-glass, hanging in the Air, and that exactly. But if an ingenious man observe it, he may wonderfully see an Image hanging in the Air, that is received in a plain Glass, and sent far out as I shewed, without the help of a Concave-glass, and a visible spectacle, by the means of a plain Glass onely. You may also

By a plain Glass see your face turned the wrong way.

When you have set the Glass to your brest, as I said; set a plain Glass against it, and look upon it, will cast it upon the Concave-glass, and that will beat it backwards on the plain Glass: so have you your purpose.

CHAP. VI.

Other operations of a Concave-Glass.

BEfore I part from the operations of this Glass, I will tell you some use of it, that is very pleasant and admirable, whence great secrets of Nature may appear unto us. As,

To see all things in the dark, that are outwardly done in the Sun, with the colours of them.

You must shut all the Chamber windows, and it will do well to shut up all holes besides, lest any light breaking in should spoil all. Onely make one hole, that shall be a hands breadth and length; above this fit a little leaden or brass Table, and glew it, so thick as a paper; open a round hole in the middle of it, as great as your little finger: over against this, let there be white walls of paper, or white clothes, so shall you see all that is done without in the Sun, and those that walk in the streets, like to Antipodes, and what is right will be the left, and all things changed; and the farther they are off from the hole, the greater they will appear. If you bring your paper, or white Table neerer, they will shew less and clearer; but you must stay a while, for the Images will not be seen presently: because a strong similitude doth sometimes make a great sensation with the sence, and brings in such an affection, that not onely when the senses do act, are they in the organs, and do trouble them, but when they have done acting, they will stay long in them: which may easily be perceived. For when men walk in the Sun, if they come into the dark, that affection continues, that we can see nothing, or very scantly; because the affection made by the light, is still in our eyes; and when that is gone by degrees, we see clearly in dark places. Now will I declare what I ever concealed till now, and thought to conceal continually. If you put a small centicular Crystal glass to the hole, you shall presently see all things clearer, the countenances of men walking, the colours, Garments, and all things as if you stood hard by; you shall see them with so much pleasure, that those that see it can never enough admire it. But if you will

See all things greater and clearer,

Over against it set the Glass, not that which dissipates by dispersing, but which congregates by uniting, both by coming to it, and going from it, till you know the true quantity of the Image, by a due appropinquation of the Centre; and so shall the beholder see more fitly Birds flying, the cloudy skies, or clear and blew, Mountains that are afar off; and in a small circle of paper (that is put over the hole) you shall see as it were an Epitomy of the whole world, and you will much rejoyce to see it: all things backwards, because they are neer to the Centre of the Glass, if you set them farther from the Centre, they will shew greater and upright, as they are, but not so clear. Hence you may,

If you cannot draw a Picture of a man or any things else, draw it by this means;

If you can but onely make the colours. This is an Art worth learning. Let the Sun beat upon the window, and there about the hole, let there be Pictures of men, that it may light upon them, but not upon the hole. Put a white paper against the hole, and you shall so long fit the men by the light, bringing them neer, or setting them further, until the Sun cast a perfect representation upon the Table against it: one that is skill'd in painting, must lay on colours where they are in the Table, and shall describe the manner of the countenance; so the Image being removed, the Picture will remain on the Table, and in the superficies it will be seen as an Image in Glass. If you will

That all shall appear right,

This is a great secret: many have tryed it, but none could obtain it: For some setting Plain Glasses obliquely against the hole, by reverberation against the Table, they could see some things somewhat direct, but dark and not discernable. I oft-times by putting a white paper obliquely against the hole, and looking just against the hole, could see some things direct: but a Pyramis cut obliquely, did shew men without proportion, and very darkly. But thus you may obtain your desire: Put against the hole a convex Glass; from thence let the Image reflect on a Concaveglass: let the Concave-glass be distant from the Centre, for it will make those Images right, that it receives turned, by reason of the distance of the Centre. So upon the hole and the white paper, it will cast the Images of the Objects so clearly and plainly, that you will not wonder a little. But this I thought fit to let you understand, lest you fail in the work, that the Convex and Concave-glasses be proportionable circles: how you shall do this, will be here declared often. I shall shew also,

How in a Chamber you may see Hunting, Battles of Enemies, and other delusions.

Now for a conclusion I will add that, then which nothing can be more pleasant for great men, and Scholars, and ingenious persons to behold; That in a dark Chamber by white sheets objected, one may see as clearly and perspicuously, as if they were before his eyes, Huntings, Banquets, Armies of Enemies, Plays, and all things else that one desireth. Let there be over against that Chamber, where you desire to represent these things, some spacious Plain, where the Sun can freely shine: Upon that you shall set Trees in Order, also Woods, Mountains, Rivers, and Animals, that are really so, or made by Art, of Wood, or some other matter. You must frame little children in them, as we use to bring them in when Comedies are Acted: and you must counterfeit Stags, Bores, Rhinocerets, Elephants, Lions, and what other creatures you please: Then by degrees they must appear, as coming out of their dens, upon the Plain: The Hunter he must come with his hunting Pole, Nets, Arrows, and other necessaries, that may represent hunting: Let there be Horns, Cornets, Trumpets sounded: those that are in the Chamber shall see Trees, Animals, Hunters Faces, and all the rest so plainly, that they cannot tell whether they be true or delusions: Swords drawn will glister in at the hole, that they will make people almost afraid. I have often shewed this kind of Spectacle to my friends, who much admired it, and took pleasure to see such a deceit; and I could hardly by natural reasons, and reasons from the Opticks remove them from their opinion, when I had discovered the secret. Hence it may appear to Philosophers, and those that study Opticks, how vision is made; and the question of intromission is taken away, that was antiently so discussed; nor can there be any better way to demonstrate both, than this. The Image is let in by the pupil, as by the hole of a window; and that part of the Sphere, that is set in the middle of the eye, stands in stead of a Crystal Table. I know ingenious people will be much delighted in this. It is declared more at large in our Opticks. From hence may one take his principles of declaring any thing to one that is confederate with him, that is secret, though the party be far off, shut up in prison. And no small Arts may be found out. You shall amend the distance by the magnitude of the Glass. You have sufficient. Others that under took to teach this, have utter'd nothing but toyes, and I think none before knew it. If you desire to know

How you may see the Sun Eclipsed,

Now I have determined to shew how the Suns Eclipse may be seen. When the Sun is Eclipsed, shut your Chamber-windows, and put a paper before a hole, and you shall see the Sun: let it fall upon the paper opposite from a Concave-glass, and make a circle of the same magnitude: do so at the beginning, middle, and end of it. Thus may you without any hurt to your eyes, observe the points of the diameter of the Suns Eclipse.

CHAP. VII.

How you may see in the dark, what is light without by reason of Torches.

VVE may demonstrate the same without the light of the Sun, not without wonder. Torches, or lights lighted on purpose in Chambers, we may see in another dark Chamber what is done, by fitting things as I said: but the light must not strike upon the hole, for it will hinder the operation; for it is a second light that carries the Images. I will not conceal at last a thing that is full of wonder and mirth, because I am faln upon this discourse,

That by night an Image may seem to hang in a Chamber.

In a tempestuous night the Image of any thing may be represented hanging in the middle of the Chamber, that will terrifie the beholders. Fit the Image before the hole, that you desire to make to seem hanging in the Air in another Chamber that is dark; let there be many Torches lighted round about. In the middle of the dark Chamber, place a white sheet, or some solid thing, that may receive the Image sent in: for the spectators that see not the sheet, will see the Image hanging in the middle of the Air, very clear, not without fear and terror, especially if the Artificer be ingenious.

CHAP. VIII.

How without a Glass or representation of any other thing, an Image may seem to hang in the Air.

BEfore I part from this Image hanging in the Air, I will shew how you may make the Images of all things seem to hang in the Air, which will be a wonder of wonders; chiefly being done without the apparition of a Glass, or a visible Object. But first we will examine what the Antients writ of this matter. One Vitellio describes the business after his fashion, thus: Fasten the segment of a Cylinder in the middle of the house, set upon a Table, or Stool, that it may glance perpendicularly upon the ground; then place your eye at some hole or chink that is somewhat distant from the Glass, and let it be fixed, that it may not move here and there: over against the Glass break the wall, and make it like to a window: let it be Pyramidal in shape, and let the sharp point be within, and the basis without, as men use to do, when a Picture or any Image is placed for the eye to look upon; but let it be reflected on by the superficies of the Pyramidal Glass, that the Picture placed without, which your eye cannot see through the hole, may seem to hang pendulous in the Air; which will cause admiration to behold. A Pyramidal Convex-glass will do the same, if you fit it so that it may represent the same Image. It may be done also by a Sphaerical Convex and Concave. But the matter promiseth more in the Frontispiece written upon it, then it will performe in the conclusion. Wherefore the Image will be seen without the Glass, but by the means of the Glass; so that the thing beheld in the Glass, will seem to be without it. But he is foully mistaken here, as in other places. He had said better, by a Cylinder of Crystal: For as a pillar it would make an irradiation outwardly, yet it would be worse seen than in the pillar, as I shall shew. But I shall discover what I purposed always to conceal;

That neither the Object nor Glass may be seen, yet the Image shall seem to hang alone, pendulous in the middle of the Chamber;

And walking about, you shall behold the Image every where. But is such a thing fit to be discovered to the people? shall I do such an unworthy Act? Ah! my pen falls out of my hand. Yet my desire to help posterity, overcomes; for perhaps from this gleaning as it were, greater and more admirable inventions may be produced. Let it be so: get not a Sphaerical Cylinder, or Convex diflection of a Pyramidal Concave, the portion of which segment is not known; but let it be that which may descend upon his right Angle by a half Cylinder and a square, and is parted by an oblique Angle. Of two parts it must be received pendulous, and beneath in the half of its diameter it is conveyed from the middle. Let all the windows of the house be shut: stop all the chinks, that the light may not come in beneath. In that place where the spectacle is prepared, if the Sun or Moon beams fall in, the whole shew is spoiled. So place the beams of the Image that are beaten back, that the head of it may by repercussion fall right upon the earth. So will the visible Object that comes by reper[…]ussion, be reflected above and beneath; It will follow the fashion of the first Glass: let a Brass or Marble Table be so placed upon it, as we said; and lest the light falling from the window should light upon the plain Cylinder, and the crooked Glass, it mu[…] be stopped by a shutter of a hands-breath, that is three times as broad as the hole; for it will break forth every way: You shall cover the apparition, that the Image may be fitted very deep, that there may seem to be a pit: as the beams meet, let the spectator come, who cannot be in any great mistake. But cover your sight round, that the Glass offend not your eye. Then is the Image seen, and it shall not appear above the Table, where the falling of the Cathetus will cut the line of sight through the Centre of the Glass. I could open the matter no plainer, I have done what I could: I know he that can understand it, will rejoyce very much.

CHAP. IX.

Mixtures of Glasses, and divers apparitions of Images.

NOw will I try to make a Glass, wherein many diversities of Images shall appear: and though such a one be hard to make, yet it will recompence all by the diversity of Images, and the benefit of it. If then you would

Make a Glass that shall represent much diversity of Images.

Take a great or small circle, as you would have your Glass, and here and there cut off two parts of the circumference, one to the quantity of a Pentagon, the other of a Hexagon, as is clear in the Mathematicks: let the arch of the Pentagon be made hollow with some table, or Iron, that it may exactly receive it into it, and may seem to be cut out of it; but the side of the Hexagon shall be contrary to this, for the quantity of that must be received by a Convex Table, that the arch of it may so stick forth: Then take a foil of Wax or Lead, of a convenient thickness, that exceeds the breadth of the arch of the Hexagon, and in length exceeds them both: Then crook this plate so, that it may exactly stand in the hollow of the wood, that there be no space or chink left between them; then let the Convex superficies that is preserved prominent, be applied inwardly, according to the breadth of it; that the form of the Concavity may not be against the Convexity, but that the same plate may receive both portions without impediment: Having thus made your model, make your Glass of steel, or of some other mixture, as I shall shew you; and when it is polished, it will shew you many diversites of Images. First, the right parts will shew right, and the left the left, whereas the nature of plain Glasses, is to shew the right side as left, and the left side as right: and if you go backwards, the Image will seem proportionable, and will come forward: if you come more towards the Convex superficies, the Image will shew ugly; and the neerer you come, the uglier will it shew, and be more like a hories head. If you incline the Glass, that will incline too; and by varying the Glass, and the situation of it, you shall perceive divers variations; sometimes the head down, and the heels up; and you shall see many other things that I think not needful to relate now: for being placed on a voluble set, that it may shew both parts before and behind, the spectator of himself may see all things. We may

Make a Glass out of all,

that in that alone all Images may be seen, that are seen in all: many mouths; sometimes greater, sometimes less, sometimes right, sometimes left, some neerer, some farther off, some equidistant. If a crooked be set in one place, in another a Concave, and a plain one in the middle, you shall see great diversity of Images. These are

The operations of a Convex Cylindrical Glass.

When your face is against it, the more deformed it appears in length, the more ugly it is for slenderness: if the length of it cut the face overthwart, it shews a low pressed down face like a Frogs, that you shall see nothing but the teeth: almost the same way, as you shall see it in a Sword, or any other long and polished steel: if you incline it forward, the forehead will appear very great, the chin small and slender like a horse. But contrary to these are

The operations of Cylindrical Concave-glasses.

If you look into the Concave, you shall see more Images of the same thing, imitating the said Glass. If you set your eye to the Centre, you shall see it all the breadth of the Glass; so your forehead, mouth, and the rest. If you turn such a Glass, that it may cut your face broad-ways, you shall presently see your head inverted, and the rest that I related in the Concave-glass.

The operations of a Pyramidal Glass turned,

are these: You shall see a sharp forehead, and a large chin. But the contrary way, a long forehead, with a very long nose. In a Concave you shall behold many faces, if according to the concavity you fit many portions of plain Glasses: for one looking into it, shall find them as many as there are Glasses, and all moving a like; and again, what Glass soever it be, if it be not plain, it shall shew always different from the Image.

CHAP. X.

Of the effects of a Lenticular Crystal.

MAny are the operations of a Lenticular Crystal, and I think not fit to pass them over in silence. For they are Concaves and Convexes. The same effects are in spectacles, which are most necessary for the use of mans life; whereof no man yet hath assi[…]n'd the effects, nor yet the reasons of them. But of these more at large in our Opticks. That no space may be empty, I shall touch some things here; I call Lenticulars, portions of circles compacted together, of Concaves and Convexes. I will first shew

How with a Convex Crystal Lenticular to kindle fire.

A Convex Lenticular kindleth fire most violently, and sooner, and more forcibly then a Concave-glass: I gave the reasons in my Opticks. For being held against the Sun, when the beams meet in the opposite part, it will kindle fire it is opposite to, melt Lead, and fire Metals. Moreover, if you will

By night give light afar off with a Lenticular Crystal,

Set a Candle a little behind the point of burning, so it will cast parallels a very great way to the opposite part, that you may see men pass the streets, and all things done in Chambers that are far from you. The same way as I said of a Concave-glass, we may

In a dark night read a letter by a Lenticular Crystal:

Put the letter behind the Glass, against the Stars or Candles a great way from you; where the beams meet, the words that are opposite will be clearly seen in a dark night, and the Chamber shut. But that which follows, will afford you a principle far better for your consideration: Namely,

By a Lenticular Crystal to see things that are far off, as if they were close by.

For setting your eye in the Centre of it behind the Lenticular, you are to look upon a thing afar off, and it will shew so neer, that you will think you touch it with your hand: You shall see the clothes colours, mens faces, and know your friends a great way from you. It is the same

To read an Epistle a great way off with a Lenticular Crystal.

For if you set your eye in the same place, and the Epistle be at a just distance, the letters will seem so great, that you may read them perfectly. But if you incline the Lenticular to behold the Epistle obliquely, the letters will seem so great, that you may read them above twenty paces off. And if you know how to multiply Lenticulers, I fear not but for a hundred paces you may see the smallest letters, that from one to another the Characters will be made greater: a weak sight must use spectacles fit for it. He that can fit this well, hath gain'd no small secret. We may

Do the same more perfectly with a Lenticular Crystal.

Concave Lenticulars will make one see most clearly things that are afar off; but Convexes, things neer hand; so you may use them as your sight requires. With a Concave you shall see small things afar off, very clearly; with a Convex, things neerer to be greater, but more obscurely: if you know how to fit them both together, you shall see both things afar off, and things neer hand, both greater and clearly. I have much helpe[…] some of my friends, who saw things afar off, weakly; and what was neer, confusedly, that they might see all things clearly. If you will, you may

By a Convex Lenticular Crystal see an Image hanging in the Air.

If you put the thing to be seen behind the Lenticular, that it may pass thorow the Centre, and set your eyes in the opposite part, you shall see the Image between the Glass and your eyes; and if you set a paper against it, you shall see it clearly: so that a lighted Candle will seem to burn upon the Paper. But

By a Concave Lenticular to describe compendiously how long and broad things are.

A Painter may do it with great commodity, and proportion: for by opposition to a Concave Lenticular, those things that are in a great Plain are contracted into a small compass by it; so that a Painter that beholds it, may with little labour and skill, draw them all proportionably and exactly: but to leave nothing concerning spectacles, I will shew

How a thing may appear multiplied.

Amongst sports that are carried about, a spectacle is of no small account: that Glass Instrument we put to our eyes, to see the better with. For of those things that delude the sight, there can be no better way invented, then by the medium; for that being changed, all things are changed. Wherefore prepare that of very solid thick Glass, that it may be the better worked by a wheel into proportions: wherefore fit it into many Forms and Angles, whereby we desire to multiply any thing: but in the middle of them, let the Angles be Pyramidal, and let it agree with the sight; that from divers Forms, Images may be retracted to the eyes, that they cannot discern the truth. Being now made of divers superficies, set them to your eyes; and if you look upon any mans face hard-by, you will think you see Argus, one that is all Eyes. If his nose, you shall see nothing but nose; so his hands, fingers, arms, that you shall see no man, but Briareus the Poet, faigned to have have an hundred hands. If you look upon Money, you shall see many for one, that you cannot touch it with your hands, but it will often deceive you; and it is better to pay with it then to receive. If you see a Galley afar off, you will think it is a fleet of war: If a Souldier walks, that it is an Army marching. And thus are things doubled, and men seem to have two faces, and two bodies, Thus are there divers ways to see, that one thing may seem to be another: and all these things will be evident to those that seek and enquire after them by tryal.