You then pa.s.s the gla.s.ses slowly through the groove, and when you come to that part where the storm is supposed to begin, move them gently up and down, which will give the appearance of the sea and vessels being agitated; increase the motion till they come to the height of the storm. You will thus have a very natural representation of the sea and ships in a calm and storm; and as you gradually draw the gla.s.ses back, the tempest will subside, the sky appear clear, and the vessels glide gently over the waves.

By the means of two or three gla.s.ses, you may also represent a battle on land, or a naval engagement, with a variety of other pleasing experiments.

_To produce the appearance of a Spectre on a Pedestal in the middle of a Table._

Enclose a small magic lantern in a box, Fig. 11, large enough to contain a small swing dressing-gla.s.s, which will reflect the light thrown on it by the lantern in such a way, that it will pa.s.s out at the aperture made at the top of the box; which aperture should be oval, and of a size adapted to the cone of light to pa.s.s through it.

There should be a flap with hinges, to cover the opening, that the inside of the box may not be seen.

[Ill.u.s.tration: Fig. 11.]

There must be holes in that part of the box which is over the lantern, to let the smoke out; and over this must be placed a chafing-dish of an oblong figure, large enough to hold several lighted coals. This chafing-dish, for the better carrying on the deception, may be enclosed in a painted tin box, about a foot high, with a hole at top, and should stand on four feet, to let the smoke from the lantern escape.

There must also be a gla.s.s planned to rise up and down in the groove _a b_, and so managed by a cord and pulley, _c d e f_, that it may be raised up and let down by the cord coming through the outside of the box. On this gla.s.s, the spectre, (or any other figure you please,) must be painted in a contracted or equal form, as the figure will reflect a greater length than it is drawn.

When you have lighted the lamp in the lantern, and placed the mirror in a proper direction, put the box on a table, and, setting the chafing-dish in it, throw some incense, in powder, on the coals. You then open the trap door and let down the gla.s.s in the groove slowly, and when you perceive the smoke diminish, draw up the gla.s.s, that the figure may disappear, and shut the trap door.

This exhibition will afford a deal of wonder; but observe, that all the lights in the room must be extinguished; and the box should be placed on a high table, that the aperture through which the light comes out may not be seen.

There are many other pleasing experiments which may be made with the magic lantern, but the limits of our work will not permit us to specify them, without excluding many other equally interesting subjects of a different nature.

_The Artificial Landscape._

Procure a box, as in Fig. 12, of about a foot long, eight inches wide, and six inches high, or any other dimensions you please, so they do not greatly vary from these proportions. At each of its opposite ends, on the inside of this box, place a piece of looking-gla.s.s that shall exactly fit: but at that end where the sight hole A is, sc.r.a.pe the quicksilver off the gla.s.s, through which the eye can view the objects.

[Ill.u.s.tration: Fig. 12.]

Cover the box with gauze, over which place a piece of transparent gla.s.s, which is to be well fastened in. Let there be two grooves at each of the places C D E F, to receive two printed scenes, as follow: On two pieces of pasteboard, let there be skilfully painted, on both sides, any subject you think proper, as woods, bowers, gardens, houses, &c.; and on two other boards, the same subjects on one side only, and cut out all the white parts: observe also, that there ought to be in one of them some object relative to the subject, placed at A, that the mirror placed at B may not reflect the hole on the opposite side.

The boards painted on both sides are to slide in the grooves C D E F, and those painted on one side are to be placed against the opposite mirrors A and B; then cover the box with its transparent top. This box should be placed in a strong light, to have a good effect.

When it is viewed through the sight hole, it will present an unlimited prospect of rural scenery, gradually losing itself in obscurity; and be found well worth the pains bestowed on its construction.

_To draw, easily and correctly, a Landscape, or any other Object, without being obliged to observe the Rules of Perspective, and without the Aid of the Camera Obscura._

[Ill.u.s.tration: Fig. 13.]

Procure a box of pasteboard, A B C D, Fig. 13, of about a foot and a half long, and made in the shape of a truncated pyramid, whose base, B D F G, is eight inches wide, and six inches high. Fix to the other end of it a tube of four or five inches long, and which you can draw out from the box more or less. Line the inside of the box with black paper, and place it on a leg or stand of wood, H, and on which it may be elevated or depressed by the hinge I.

Take a small frame of wood, and divide it at every inch by lines of black silk drawn across it, forming forty-eight equal parts; divide these into still smaller equal parts, by lines of finer silk:[C] fix this frame at the end of B D, as the base of the pyramid.

Provide a drawing-paper, divided into the same number of parts as in the frame, by lines, lightly drawn in pencil. It is not material of what size these divisions are; that will depend entirely on the size you propose to draw the objects by this instrument.

Place this instrument opposite a landscape, or any other object that you want to draw, and fix the leg firmly on, or in the ground, that it may not shake; then turning it to the side you choose, raise or incline it, and put the tube further in or out, till you have gained an advantageous view of the object you intend to draw.

Place your eye, E, by the instrument, which you have adjusted to the height of your eye, and, looking through the tube, carefully observe all that is contained in each division of the frame, and transpose it to the corresponding division in your paper; and if you have the least knowledge in painting or even drawing, you will make a very pleasing picture, and one in which all the objects will appear in the most exact proportion.

By the same method you may draw all sorts of objects, as architecture, views, &c., and even human figures, if they remain some time in the same att.i.tude, and are at a proper distance from the instrument.

[C] The different thicknesses of the silk serve to distinguish more readily the corresponding divisions.

_Illuminated Prospects._

Provide yourself with some of those prints that are commonly used in optical machines, printed on very thin white paper; taking care to make choice of such as have the greatest effect from the manner in which the objects are placed in perspective. Place one of these on the borders of a frame, and paint it carefully with the most lively colours, making use of none that are terrestrial. Observe to retouch those parts several times where the engraving is strongest,[D] then cut off the upper part or sky, and fix that on another frame.

[Ill.u.s.tration: Fig. 14.]

[Ill.u.s.tration: Fig. 15.]

The prints being thus prepared, place them in a box, A B C D, Figs. 14 and 15, the opening to which, E F G H, should be a little less than the print. Cover this opening with a gla.s.s, and paint all the s.p.a.ce between that and the prints, which should be about two or three inches, black. The frame that contains the sky should be about an inch behind the other. In the back part of this box, which is behind the prints, and which may be about four inches deep, place four or five small candlesticks to hold wax lights, and cover that part entirely with tin, that it may be the more luminous.

When the print is placed between the wax lights and the opening in the front of the box, and there is no other light in the room, the effect will be highly pleasing; especially if the lights are at a sufficient distance from each other, and not too strong, that they may not occasion any blots in the print. Those prints that represent the rising or setting of the sun will have a very picturesque appearance.

Such as represent conflagrations have also a striking effect.

There should be two grooves for the print next the gla.s.s, that you may insert a second subject before you draw away the first; and that the lights in the back of the box may not be discovered.

You must not, thinking to make the print more transparent, cover it with varnish; for that will prevent the gradation of the colours from being visible. The frame should enter the side of the box by a groove, that a variety of subjects may be introduced.

[D] When you colour a print, place it before you, against a piece of gla.s.s, in a position nearly erect, that it may be enlightened by the sun. You may also colour both sides of the print.

EXPERIMENTS IN MAGNETISM.

_The Magnetic Wand._

Bore a hole three-tenths of an inch in diameter, through a round stick of wood; or get a hollow cane about eight inches long, and half an inch thick. Provide a small steel rod, and let it be very strongly impregnated with a good magnet: this rod is to be put in the hole you have bored through the wand, and closed at each end by two small ends of ivory that screw on, different in their shapes, that you may better distinguish the poles of the magnetic bar.

When you present the north pole of this wand to the south[E] pole of a magnetic needle, suspended on a pivot, or to a light body swimming on the surface of the water, (in which you have placed a magnetic bar,) that body will approach the wand, and present that end which contains the south end of the bar: but if you present the north or south end of the wand to the north or south end of the needle, it will recede from it.

[E] For the more clearly explaining this, it is to be observed, that the two ends of a magnet are called its poles.

When placed on a pivot, in just equilibrium, that end which turns to the north is called the north pole, and the other end the south pole.

_The Mysterious Watch._

You desire any person to lend you his watch, and ask him if it will go when laid on the table. He will, no doubt, say it will; in which case, you place it over the end of the magnet, and it will presently stop.

You then mark the precise spot where you placed the watch, and, moving the point of the magnet, you give the watch to another person, and desire him to make the experiment; in which he not succeeding, you give it to a third (at the same time replacing the magnet) and he will immediately perform it.

This experiment cannot be effected, unless you use a very strongly impregnated magnetic bar, (which may be purchased at the opticians',) and the balance of the watch must be of steel, which may be easily ascertained by previously opening it, and looking at the works.

_The Magnetic Dial._