[Ill.u.s.tration: Fig. 25.]

_To show the Spots in the Sun's Disk by its Image in the Camera Obscura._

Put the object-gla.s.s of a ten or twelve feet telescope into the scioptric ball, and turn it about till it be directly opposite the sun. Then place the pasteboard mentioned in page 16, in the focus of the lens, and you will see a clear bright image of the sun, about an inch diameter, in which the spots on the sun's surface will be exactly described.

As this image is too bright to be seen with pleasure by the naked eye, you may view it through a lens whose focus is at six or eight inches distance, which, while it prevents the light from being offensive, will, by magnifying both the image and the spot, make them appear to greater advantage.

_The Diagonal Opera Gla.s.s._

By the diagonal position of a plane mirror, a curious opera-gla.s.s is constructed, by which any person may be viewed in a theatre or public company without knowing it. It consists only in placing a concave gla.s.s near the plane mirror, in the end of a short round tube, and a convex gla.s.s in a hole in the side of the tube, then holding the end of the tube with the gla.s.s to the eye, all objects next to the hole in the side will be reflected so as to appear in a direct line forward, or in a position at right angles to the person's situation who is looked at. Plane gla.s.ses, instead of a convex and concave, may be used; in this case the size of the object will not be increased, but it will appear brighter.

_To observe an Eclipse of the Sun, without Injury to the Eye._

Take a burning-gla.s.s, or spectacle-gla.s.s, that magnifies very much; hold it before a book or pasteboard, twice the distance of its focus, and you will see the round body of the sun, and the manner in which the moon pa.s.ses between the gla.s.s and the sun, during the whole eclipse.

_The Burnt Writing restored._

Cover the outside of a small memorandum book with black paper, and in one of its inside covers make a flap, to open secretly, and observe there must be nothing over the flap but the black paper that covers the book.

Mix soot with black or brown soap, with which rub the side of the black paper next the flap; then wipe it clean, that a white paper pressed against it will not receive any mark.

Provide a black-lead pencil that will not mark without pressing hard on the paper. Have likewise a small box, about the size of a memorandum book, and that opens on both sides, but on one of them by a private method. Give a person a pencil and a slip of thin paper, on which he is to write what he thinks proper; you present him the memorandum book at the same time, that he may not write on the bare paper. You tell him to keep what he writes to himself, and direct him to burn it on the iron plate laid on a chafing-dish of coals, and give you the ashes. You then go into another room to fetch your magic box, before described, and take with you the memorandum book.

Having previously placed a paper under the flap in the cover of the book, when he presses hard with the pencil, to write on his paper, every stroke, by means of the stuff rubbed on the black paper, will appear on that under the flap. You therefore take it out, and put it into one side of the box.

You then return to the other room, and taking a slip of black paper, you put it into the other side of the box, strewing the ashes of the burnt paper over it. Then shaking the box for a few moments, and at the same time turning it dexterously over, you open the other side, and show the person the paper you first put in, the writing on which he will readily acknowledge to be his.

If there be a press or cupboard that communicates with the next room, you need only put the book in the press, and your a.s.sistant will open it, and put the paper in the box, which you presently after take out, and perform the rest of the amus.e.m.e.nt as before.

There may likewise be a flap on the other cover of the book; and you may rub the paper against that with red lead. In this case you give the person the choice of writing either with a black or red pencil; and present him the proper side of the book accordingly.

_The Opaque Box made Transparent._

Make a box three or four inches long, and two or three wide, and have a sort of perspective-gla.s.s, the bottom of which is the same size with the box, and slides out, that you may privately place a paper on it.

The sides of this perspective are to be of gla.s.s, covered on the inside with fine paper.

Let a person write on a slip of paper, putting your memorandum book under it, as in the last amus.e.m.e.nt; then give him the little box, and let him put what he has written into it. In the mean time you put the memorandum book into the press, where the perspective is already placed. Your a.s.sistant then takes the paper out of the book, and puts it at the bottom of the perspective; which you presently take out of the press, and direct the person to put the little box that contains the paper under it. You then look in at the top of the perspective, and feigning to see through the top of the box, you read what is written on the paper at the bottom of the perspective.

With this perspective box you may perform another amus.e.m.e.nt, which is, by having in a bag twelve or more ivory counters, numbered, which you show to the company, that they may see all the numbers are different.

You tell a person to draw any one of them, and keep it close in his hand. You then put the bag in the press, when your a.s.sistant examines the counters, and sees which is wanting, and puts another of the same number at the bottom of the perspective, which you then take out, and placing the person's hand close to it, look in at the top, and pretending to see through his hand, you name the number on the counter in it.

_The Transposable Pieces._

Take two guineas and two shillings, and grind part of them away, on one side only, so that they may be but half the common thickness; and observe, that they must be quite thin at the edge; then rivet a guinea and a shilling together. Lay one of these double pieces, with the shilling upwards, on the palm of your hand, at the bottom of your three first fingers, and lay the other piece with the guinea upwards in the like manner, in the other hand. Let the company take notice in which hand is the guinea, and in which is the shilling. Then as you shut your hands, you naturally turn the pieces over, and when you open them again, the shilling and the guinea will appear to have changed their places.

_The Penetrative Guinea._

Provide a large tin box, of the size of a large snuff-box, and in this place eight other boxes, which will go easily into each other, and let the least of them be of a size to hold a guinea. Each of these boxes should shut with a hinge, and to the least of them there must be a small lock, that is fastened with a spring, but cannot be opened without a key;--observe, that all these boxes must shut so freely, that they may be all closed at once. Place these boxes in each other, with their tops open, in the drawer of the table on which you make your experiments; or, if you please, in your pocket, in such a manner that they cannot be displaced.

Then ask a person to lend you a new guinea, and desire him to mark it, that it may not be changed. You take this piece in one hand, and in the other you have another of the same appearance, and putting your hand into the drawer, you slip the piece that is marked into the least box, and shutting them all at once, you take them out; then showing the piece you have in your hand, and which the company suppose to be the same that was marked, you pretend to make it pa.s.s through the box, and dexterously convey it away.

You then present the box, for the spectators do not yet know there are more than one, to any person in company, who, when he opens it, finds another, and another, till he comes to the last, but that he cannot open without the key, which you then give him, and retiring to a distant part of the room, you tell him to take out the guinea himself, and see if it be that which he marked.

This amus.e.m.e.nt may be made more surprising, by putting the key into the snuff-box of one of the company, which you may do by asking him for a pinch of snuff, and at the same time conceal the key, which must be very small, among the snuff; and when the person, who is to open the box, asks for the key, you tell him that one of the company has it in his snuff-box. This part of the amus.e.m.e.nt may likewise be performed by means of a confederate.

_To make Pictures of Birds with their Natural Feathers._

First take thin board or panel, of deal or wainscot, well seasoned, that it may not shrink; then paste white paper smoothly on it, and let it dry; if the colour of the wood show through, paste a second paper over it. When the paper is dry, get ready any bird that you would represent, and draw the outline as exact as you can on the papered panel. You then paint the ground-work, stump of a tree, the bill and legs, their proper colour, with water-colours, leaving the body to be covered with its own natural feathers. In the s.p.a.ce you have left for the body, you lay on very thick gum-water, letting each coat dry before you lay on another, and so continuing until the gum is as thick as a shilling. Then take the feathers off the bird; and, as you proceed, draw a camels'-hair pencil, dipped in gum-water, over the coat of gum that you have laid on the paper, that it may more readily adhere. As you strip the bird, you must fix the feathers in their proper places on the board, and you shave the shafts or stems of the larger feathers, that they may lie flat. The most ready way to perform the operation, is to provide yourself with a pair of steel pliars to take up and lay on the feathers with. You should prepare some small leaden weights to lay on the feathers, that they may more readily adhere to, and lie flat on, the gum. The part where the eye is must be supplied by a small piece of paper, coloured and shaped like one; or you may, probably, be able to get a gla.s.s bead that will answer the purpose better. In order that the feathers may lie smooth and regular, when the whole is perfectly dry, lay a book, or a flat board, with a weight on it.

_The Art of Bronzing._

Bronzing is that process by which figures of plaster-of-paris, wood, &c. are made to have the appearance of copper or bra.s.s. The method is as follows:

Dissolve copper filings in aqua fortis. When the copper has impregnated the acid, pour off the solution, and put into it some pieces of iron, or iron filings. The effect of this will be to sink the powder to the bottom of the acid. Pour off the liquor, and wash the powder in successive quant.i.ties of fresh water. When the powder is dry, it is to be rubbed on the figure with a soft cloth, or piece of leather; but observe, that previously to the application of the bronze powder, a dark blackish sort of green is first to be laid on the figure: and if you wish the powder to adhere stronger, mix it with gum-water, lay it on like paint, with a camels'-hair brush, or previously trace the parts to be bronzed with gold size, and when nearly dry, rub the powder over it.

_Method of taking the Impression of b.u.t.terflies on Paper._

Clip the wings off the b.u.t.terfly, lay them on clean, in the form of a b.u.t.terfly when flying. Spread some thick clean gum-water on another piece of paper, press it on the wings, and it will take them up; lay a piece of white paper over it, and rub it gently with your finger, or the smooth handle of a knife. The bodies are to be drawn in the s.p.a.ce which you leave between the wings.

_To soften Horn._

To one pound of wood-ashes, add two pounds of quick lime; put them into a quart of water. Let the whole boil till reduced to one-third.

Then dip a feather in, and if, on drawing it out, the plume should come off, it is a proof that it is boiled enough; if not, let it boil a little longer. When it is settled, filter it off, and in the liquor thus strained put in shavings of horn. Let them soak for three days; and, first anointing your hands with oil, work the horn into a ma.s.s, and print or mould it into any shape you please.

_To make Moulds of Horn._

If you wish to take the impression of any coin, medal, &c., previously anoint it with oil; then lay the horn shavings over it in its softened state. When dry, the impression will be sunk into the horn; and this will serve as a mould to re-produce, either by plaster-of-paris, putty and glue, or isingla.s.s and ground egg-sh.e.l.ls, the exact resemblance of the coin or medal.

_To cast Figures in Imitation of Ivory._

Make isingla.s.s and strong brandy into a paste, with powder of egg-sh.e.l.ls, very finely ground. You may give it what colour you please; but cast it warm into your mould, which you previously oil over. Leave the figure in the mould till dry, and you will find, on taking it out, that it bears a very strong resemblance to ivory.

_To extract the Silver out of a Ring that is thick gilded, so that the Gold may remain entire._