Fig. 11.—The swimming paper fish.
You are now ready to set the fish in motion; but to add to the interest of the experiment, challenge any of your friends to make the fish move without touching or even blowing upon it.
This may seem to them impossible. This is how it is performed.
Fig. 12.—The swimming fish.
With great care pour one large drop of oil into the opening (A); the oil at once tries to spread over the surface of the liquid, but that is only possible if it escapes by the narrow passage (A B).
This it does, and owing to the reaction the fish is thrust in the direction opposite to the flowing of the oil—i.e. it will be thrust forward, the movement lasting long enough for the spectators to view with astonishment the unusual sight of a paper fish swimming (Fig. 12).
Floating Pins and Needles
Fig. 13.—The floating pin.
If a drop of water is placed on glass it will at once spread, but if the same thing is done with a drop of mercury, the liquid will not spread, but remain in the form of a bead.
These two different results are due to the fact, that whilst the water wets the glass the mercury does not.
Now take a pin which has been well dried; it is a body which water will moisten, but owing to its very smooth surface, not so easily as in the case of glass.
Suppose, then, that by some means or other you can place the pin so gently on the surface of the liquid that the water does not make it wet, you will notice that the water takes on either side of the pin a convex shape, and in this way a sufficient volume of water is displaced to allow the pin to float as if it were a match.
The experiment may, of course, be as easily performed with a needle; nor must it be thought it is confined to pins and needles which are thin, for, with care, you may even succeed with big darning-needles.
It has not yet been shown, however, how to place the pin on the water in such a manner that it is not made even wet.
There are several ways of doing this, some requiring considerable practice.
The following is the simplest.
Float on the surface of the water a cigarette paper; place the pin upon it; leave the paper to sink to the bottom when it has become soaked, and the pin will float without any difficulty, for on either side of the pin the water takes the convex shape before mentioned, thus displacing sufficient water to allow the pin to float.
In order to hide from the spectators the stratagem you have employed, gently remove the paper before showing them the floating pin.
Joined by Air
The picture below is not taken from a prospectus advertising cement for joining glass and porcelain, but is simply used to show how atmospheric pressure may be utilized for joining glasses and plates.
In order to accomplish this it is necessary to form a vacuum, but as an air-pump is not at the disposal of every boy a partial vacuum must suffice.
To obtain this partial vacuum suspend a glass from the ceiling, or any other suitable place, by means of a string, and under it burn a piece of paper. This will cause the air it contains to expand. Immediately afterwards place the plate over the mouth of the glass, and it will adhere quite firmly.
In order to prevent the entrance of any external air, and thus destroy the vacuum, the edges of the glass may be smeared with tallow.
Now, how is it that the glass and plate are so easily fixed? Well, directly the hot air contained in the glass comes in contact with the cold surface of the plate, the air contracts, and as the plate prevents the entrance of any more air, a partial vacuum is formed within the glass.
Fig. 14.—Joined by air.
As the atmospheric pressure is much greater than the pressure from within, the plate remains firmly fixed to the glass (Fig. 14).
Glass Raising Extraordinary
This experiment, similar in principle to the last, is quite as striking in its effect.
It consists of raising in air a glass filled with water, by causing it to adhere to the hand when the latter is held quite open.
With the last experiment fresh in our minds, it is not difficult to guess that this phenomenon is due to the existence of a partial vacuum under the hand, but it is not so easy to know how to obtain this vacuum.
The means of carrying out the experiments are as follows:—
Put the glass filled with water on the table, and over the top place the palm of the hand, taking care that the four fingers are bent almost at right angles, as shown in the first of the accompanying figures (Fig. 15).
If, continuing to press the palm of the hand on the edge of the glass, you raise the four fingers quickly, thus having the palm stretched out, you will force out most of the air which is between your palm and the surface of the water, and in this way you will produce under your hand a partial vacuum. This vacuum will be sufficient to allow the atmospheric pressure to overcome the weight of the glass and its contents; thus a sucker is formed which allows the glass to remain attached to the hand (Fig. 16).
Fig. 15.—Glass raising extraordinary.
Fig. 16.—Glass raising extraordinary.
A Novel Glass Emptier
If you are given a glass filled with water, and a bottle equally full, and then asked to empty the glass by means of the bottle, and that without emptying the bottle itself, you will imagine you have been set a very difficult task indeed.
Fig. 17.—The glass-emptying bottle.
You will soon see, however, that the solution to this seemingly difficult experiment is quite simple.
First take a cork, and in it pierce two holes. Through these gently push two straws, one being as long as the glass, the other considerably longer (Fig. 17).
By means of a pellet of bread or wax close the opening of the shorter straw, and push the cork into the bottle until the water gushes out of the longer straw.
In order to empty the glass it is now only necessary to turn the bottle upside down, in such manner that the little straw touches the bottom of the glass.
Then, taking a pair of scissors, cut this straw very near the end which is sealed.
Immediately the water in the glass will flow out by the long straw until the glass is quite empty, despite the fact that the bottle has remained full all the time (Fig. 18).
Now for a few words of explanation, in order to make clear the reason for this unexpected action.
The two straws form the two arms of a siphon, and as they are full of water it is not necessary to remove any air from them.
Fig. 18.—A novel glass-emptier.
As the liquid flows out of the long straw, it tends to produce in the bottle a vacuum. As a vacuum is contrary to nature, it is immediately destroyed by the entrance of an equal quantity of water from the little straw, for the atmospheric pressure exerted on the water in the glass keeps this little straw continually full. In this way all the water is drawn from the glass by the bottle filled with water.
A Striking Siphon Experiment
A very pretty experiment with the siphon may be performed by making use of the following simple apparatus: An ordinary glass; a little water colored, say with aniline; a piece of rubber tubing about an inch long, one end of which is cut obliquely, as shown in the diagram; together with a piece of glass tubing from four to five feet long.
Fig. 19.—A siphon experiment.
This tubing may be obtained from almost any druggist.
Prepare for your experiment by taking the length of tubing and, with a gas flame, drawing one end out to a point.
Having done this, bend the tube twice, as shown in Fig. 19, particular care being taken to avoid any sharp angles. The bending of this tubing is easily done by holding it in a gas or spirit-lamp flame until the flame is colored yellow. The glass is then soft enough to be gently bent to the required angle.
Over the end which is not pointed slip the piece of india-rubber tubing, and then place this end in the colored water.
By applying suction to the pointed end of the tube with your mouth, the siphon may be set in motion.
If now you so arrange the tube that the oval opening is partly out of water, the flowing liquid will draw in bubbles of air which, passing alternately down the tube with the drops of colored water, produce a very pretty result.
The shape and size of the air bubbles may be altered at any time by raising or lowering the tube, and this will add to the effect of the experiment.
The experiment may be again varied by removing the tube from the liquid, and before lowering it again, allowing 10 or 12 inches of air to enter. This long bubble will be seen to pass slowly down the tube until it arrives at the small opening, when it will be expelled at a great rate. The liquid following this bubble acquires the same velocity, and, arriving at the point, is ejected with such force that it will rise to a height of 6 or 7 feet.
An Electric Fountain
Most of you would like to make an electric fountain, especially when you learn how simple and easily arranged is this striking experiment. Your apparatus consists solely of a glass, a long india-rubber tube, with two small glass tubes and a piece of sealing-wax (a stick of sulphur or piece of vulcanite will do just as well).
Make a small nozzle by drawing out a length of bent glass tubing, and, by means of a long piece of india-rubber piping, fix it to another piece of bent glass tubing. Place the first piece of tubing bent at two right angles over the side of a glass filled with water, taking care that the reservoir thus formed is from 3 to 4 feet above the nozzle (Fig. 20).
When the fountain is playing the issuing jet of water will be inclined to one side.
Now to electrify the fountain. Take the piece of sealing-wax, vulcanite, or sulphur, and, after seeing that both your hand and the material you hold are perfectly dry, rub the sealing-wax on the sleeve of your coat.
Fig. 20.—An electric fountain.
If now you hold the sealing-wax opposite the stream of water, at a distance of a few feet, a remarkable change will come over the cascades. Instead of the water falling in scattering drops, these latter will at once unite, and descend in a solid stream, whilst directly the sealing-wax is removed the jet of water returns to its original form. If the water be allowed to fall on a piece of stiff paper, a difference in sound will be noticed according as the water falls in a stream or in drops.
The Bottle Cannon
Doubtless you would like to have at home the experience of firing a cannon, of hearing a report loud enough to frighten nervous persons, to see the shell fly as quick as lightning, and then to witness the recoil of your home-made piece of artillery.
Your apparatus will be quite simple, for you must first take a strong bottle, such as a vinegar, or better still, a champagne bottle, and fill it a third full with water.
Next take a little carbonate of soda, and also some tartaric acid, both of which may be obtained at any druggist’s, taking care to wrap them in packets which will not be confused one with the other.
Dissolve the carbonate of soda in the water contained in the bottle, at the same time placing the tartaric acid in a playing card rolled in the form of a cylinder, one end of which should be filled with a plug of blotting-paper.
Fig. 21.—The bottle cannon.
Having accomplished this much to your satisfaction, suspend the cartridge just made from the cork of the bottle by sticking in it a pin to which is attached a thread, particular care being taken that the bottle is standing upright on the table, and that the open end of the tube is the upper one.
After having regulated the length of the thread so that the bottom of the tube does not touch the liquid in the bottle, tightly fit the cork in.
You now have your cannon charged, and all that remains to be done is to fire it.
This is done by laying the bottle horizontally on two pencils placed parallel to one another, thus forming a gun-carriage. Immediately the bottle is so placed, the water penetrates the tube, and dissolves the tartaric acid. The carbonic acid gas which is immediately produced blows out the cork with a violent explosion, whilst at the same time, owing to the reaction, the bottle rolls back on the two pencils, in exact imitation of the recoil of a piece of artillery (Fig. 21).
CHAPTER XXXVII
SAFE CHEMICAL EXPERIMENTS
Twentieth-Century “Black Art”
As we stand in the twentieth century and peer curiously down the corridors of Time, we find at all periods a deep interest in chemical phenomena.
From the age when wisdom devoted itself in vain to the discovery of an elixir of life and a method of transmuting the base metals into gold, to the present day, when scientists pursue their experiments with more reasonable and far worthier hopes, chemistry appears never to have suffered any dearth of devotees, despite the fact that in olden times one had either to occupy a high position or be a man greatly daring if the Black Art was to be followed without fear of molestation.
To-day matters are different, so that the junior chemist need only anticipate interference from materfamilias—a truly excellent person, who, however, invariably regards chemical concoctions with hostile contempt.
The obstacles instanced in the previous paragraph being foreseen, perhaps no better initiative can be taken than to conciliate the household deities by the performance of some particular experiment which has an obviously beneficial result. This might happily be the removal of ink stains from white linen; and naturally, if no cloth happen to be so disfigured, some arrangement must be made whereby the ink is accidentally spilt!
Experiments with Chlorine
(1) Apparatus.—Erect a 4-oz. round-bottom flask about 8 inches above the table (A, Fig. 1), by clamping its neck in a wooden clip or twisted stiff iron wire, and fastening this to a firm standard. Introduce three or four tablespoonfuls of powdered manganese dioxide (obtainable cheaply in qr. lbs. at most druggists’), and pour over this spirits of salt until the flask is one-third full. Into the neck now fit a cork provided with two circular holes, through one of which a stem funnel passes, and into the other a glass tube fits tightly, being bent at two right angles, as shown in Fig. 1. The glass tube may be readily bent by softening it first over a spirit lamp—the flame being colored distinct yellow when the glass reaches a pliable state. Slide a 41⁄2-inch disc of paper (B, Fig. 1) on the free limb of the tube, and also soak several 4-inch circles of cardboard in water. These will make satisfactory covers for the small glass preserve jars, in which the gas is to be collected.
Fig. 1.—Apparatus for chlorine experiments.
(2) Preparation.—Place one jar beneath the glass tube so that the latter’s orifice reaches nearly to the bottom, and slide the paper disc down until it covers the mouth of the jar C. On warming the glass flask gently with a spirit lamp or, if available, Bunsen gas flame, a greenish-yellow gas is evolved, and gradually expels the air from flask, tube, and jar, until this latter is filled with heavy chlorine. The warming is then interrupted whilst the one jar is removed, covered with a moist cardboard disc, and replaced by another. The heating again proceeds, and so on until each remaining jar is successively filled.
Fig. 2.—The unalterable postmark.
Chlorine Experiments (1).—Damp an addressed envelope, received through the post, by pressing between sheets of wet blotting-paper, and stand it in a jar of chlorine with the cover replaced (A, Fig. 2). The writing ink address will soon begin to fade and finally disappear, whilst the postmark, which has been impressed in indelible printing ink, remains unaltered. This reaction shows that chlorine possesses the valuable property of bleaching writing ink. It may be turned to account in removing stains from cloth by wetting the spoiled material first and then standing in a vessel containing the yellow gas (Fig. 3). The fabric must be quite damp, however, as bleaching only proceeds in the presence of moisture. Coloring matters, other than black ink, are readily removed by chlorine, as may be strikingly shown by steeping a wet rose blossom or bunch of violets in a jar of the gas (Fig. 4); the flowers assume a transparent waxy appearance, that will puzzle any spectator as to their real identity.
Fig. 3.—Removing stains from linen by means of chlorine.
Fig. 4.—The transparent rose.
Chlorine Experiments (2).—The energetic gas attacks many substances spontaneously. If thin blotting-paper be soaked in turpentine, drained, and dropped into a jar of chlorine, the oil takes fire at once, burning rapidly amid smoky black fumes. Metals are attacked just as readily as the inflammable oil of turpentine. Powdered antimony metal or iron filings shaken into a jar of chlorine scintillate brilliantly with the evolution of thick white fumes. Similarly Dutch metal leaf, used for gilding cheap picture frames, ignites in the gas; a salt of copper being precipitated to the bottom of the jar when the action has ceased.
All dealings with chlorine should be conducted in a well ventilated—even draughty—room, and care must be taken not to inhale the gas. It corrodes animal tissues just as eagerly as it attacks turpentine and metals. The gas is very heavy, however, and is therefore the less difficult to keep under control.
Niter Paper.—Touch-paper burns quickly, surely, and without flame. It is prepared by soaking thin tissue paper with a saturated solution of saltpeter in weak vinegar, and when dry feels rough and crisp to the touch. Moreover, it burns with a rather pleasant smell. The advertisement scheme of bygone days, wherein a lighted match was placed on a particular spot of a paper sheet, and thence the name of the advertised commodity gradually burnt itself out over the surface, was a modification of this preparation (Fig. 5). The name or design is simply drawn with a pointed stump of wood dipped repeatedly in the saltpeter solution, and the starting-point marked conspicuously by a cross or black spot. When dry a match is applied to this mark. If there is a tendency for other parts of the paper than the design itself to burn, a short immersion in dilute alum solution, when the saltpeter lines have dried, may be resorted to.
Fig. 5.—A niter paper experiment.
Electric Fire.—This compound is in no way of an electric nature, except that it burns rapidly with brilliant blue illumination. The constituents are flowers of sulphur, saltpeter, and antimony, four parts of the former being intermingled with ten parts of powdered saltpeter, and then one-seventh the total quantity of powdered antimony finally added. Thorough mixing by gentle stirring must be insured. A good method of firing the powder is to pack it round a twist of touch-paper in a small mustard tin, threading the fuse (A, Fig. 6) through a hole in the lid, so that it may be lighted easily. The mixture burns not only brightly, but with intense heat—sufficient to melt the thin iron of the inclosing tin.
Fig. 6.—Lighting electric fire.
Fig. 7.—A sodium or potassium experiment.
The Lightest Element.—Hydrogen is a gas at ordinary temperature, and has the honor of being the lightest element, for all practical purposes, known. For this reason it finds wide employment in filling balloons and airships. The most common methods of preparation consist of decomposing water or an acid in their several constituents, either by the influence of electricity or the reaction of a metal. For instance, if a pea’s bulk of sodium or potassium metal be thrown into a basin of water, A, Fig. 7, (the experimenter should not bend directly over the vessel), a violent reaction ensues, the metal decomposes and hustles round the surface as though in feverish excitement, and in the case of potassium a purple flame springs up spontaneously. The sodium may also be ignited if it is thrown on to a floating piece of blotting-paper, or if the water be thickened with starch. This metal burns with a yellow flame, or rather colors the hydrogen flame yellow.
Fig. 8.—An interesting hydrogen experiment.
Preparing hydrogen by the foregoing method is inconvenient and expensive if any quantity is to be collected, and so in this case the following plan is usually adopted:—Support a flask (A, Fig. 8), and place zinc chips (B) in it to the depth of about 1⁄4 inch. Fit the mouth with a cork, through which passes a delivery tube (C) and a “thistle” funnel (D), dipping nearly to the level of the zinc. When the gas is required, dilute sulphuric acid—one part oil of vitriol to ten parts water—is poured down the funnel until the flask is about one-third filled (E).
Five or ten minutes should be allowed after bubbling has commenced before an attempt is made to light the gas at the delivery tube, as otherwise air from the flask may be intermingled in the exact proportion to cause a bad explosion. No danger need be feared if several minutes are allowed for the air to be thoroughly dispelled, or, as an additional measure of safety, a damp towel (F) is wrapped round the flask to prevent scattering of the glass in the event of a mishap. The glass delivery tube should have been softened in a spirit flame and drawn to a fine point where the hydrogen issues. The gas will be found to burn with an almost colorless flame.
If a glass tube (A) of larger bore than the delivery pipe be slid over this latter while the gas burns, a peculiar musical note is produced—hollow-sounding and shrill (Fig. 9). It is caused by the rapid succession of slight explosions which constitute the combustion of hydrogen.
Fig. 9.—A musical flame.
The extreme lightness of hydrogen, as well as its combustibility, is well illustrated by blowing a soap bubble. Connect a clay pipe with the glass delivery tube by means of a length of india-rubber tubing, and provide this latter with a small clip—tie-clip, for example—so that the gas supply may be shut off at will (Fig. 10). Let the hydrogen pass for a minute or so, to clear air out of the clay pipe, and then, having shut off the gas, dip the pipe bowl into soap-suds. Next open the clip until the hydrogen has blown the bubble large enough, and then shut off, shaking the shimmering globe free. It will rise very quickly, just like an unballasted balloon, and if a lighted taper be applied to its surface it will explode to annihilation with a loud report.
Fig. 10.—To explode a soap bubble.
Fig. 11.—Freezing a flask of ammonia to a block of wood.
Spirits of Hartshorn.—Commercial ammonia is actually an aqueous solution of the gas, which dissolves to an abnormal extent in water. When it has been absorbed as much as possible the liquid weighs only 22.25 as much as an equal bulk of water, owing, of course, to the latter’s association with a compound far lighter than itself. So great is the energy of solution that heat is dissipated from the liquid as absorption proceeds. Conversely, if the gas be dispelled by blowing air through strong liquor ammoniac, heat is rapidly absorbed at the expense of surrounding objects. To show this, stand a small flask in a pool of water on a wood block, and having about half filled the flask with fresh ammonia, blow into this through a glass tube connected with the mouth by a length of rubber tubing (Fig. 11). No long time should elapse before enough heat has been abstracted from the water to convert it into ice, so that the flask is frozen firmly to the wood.
Another demonstration of water’s avidity for ammonia gas is afforded by the following performance. Erect one large flask (A) in an inverted position, so that the distance between its neck and the table is several inches greater than its own height. Some distance away, as shown in Fig. 12, erect a small 4-oz. flask (B), and half fill it with a mixture of four parts sal-ammoniac to three parts slaked lime (C). Fit the neck with a cork and a delivery tube, which has been so bent as to pass through a stopper in the mouth and reach nearly to the bottom of a jar (D) packed with quicklime (E).
Another glass tube (F) issues from this chamber—but only from just below the cork’s under surface—and passes upwards into the orifice of the large flask. A square of paper (G, in Fig. 12) is pushed over the glass tube and presses against the mouth of the flask.
Fig. 12.—To prove water’s affection for ammonia.
If now the mixture in the 4-oz. flask be warmed, ammonia gas is produced, and having been robbed of moisture by the quicklime through which it passes, travels upwards, and collects in the large inverted flask. When the action has continued for a little while, stop the heating and remove the delivery tube, and bring an open spirits of salt bottle near the inverted flask’s mouth. If dense white fumes are immediately formed, the flask is known to be filled with ammonia gas, and must be corked up.
Fig. 13.—A novel fountain.
Beneath this container is next stood another large flask filled with red litmus solution (A) and fitted with a stopper, through which pass two glass tubes (M and N, in Fig. 13). One of these (N) is bent outwards, and extends only just inside the flask’s neck, whilst the other is long enough to reach from the bottom of the lower flask almost to the top of that holding the ammonia. Instead of red litmus solution, a liquid made by boiling red cabbage leaves in water, and adding just enough vinegar to dispel entirely the bluish coloration, may be used with equal success.
The position then is that two flasks—of which the upper (B) holds ammonia gas, whilst the lower retains a pink solution—are supported one above the other, their necks approaching and joined by a glass tube (M). A second glass tube (N) also emerges from just above the surface of the pink liquid, and is bent outwards from the flask, so that it may be held in the mouth. When this is blown through, the pink water is forced up the connecting tube (M) and sprays out, fountain-like, within the upper flask. Moreover, as the ammonia is so rapidly absorbed by the incoming water, this continually ascends to fill the vacuum, which tends to form as the gas is dissolved. The fountain continues to play when the blowing has ceased, and further, although the spray presents a reddish tinge on entering the flask, it immediately turns blue as the ammonia dissolves (C, Fig. 13). This reaction indicates the alkalinity of ammonia, such substances being capable of neutralizing acids, which redden solutions of vegetable blues.
CHAPTER XXXVIII
ODD EXPERIMENTS
To While Away Winter Hours
The famous King Belshazzar was much dismayed to see the mysterious writing upon the wall of his palace. Without reducing your friends to a similar state of terror, a very easy experiment can be performed productive of the same effect, and if it does not exactly make their knees strike together, it will astonish them very much.
The appliances are such as can be found in any home, and the strange writing can be produced in the following way.
Fig. 1.—Showing relative positions of candle and mirror so that patch of light is thrown on the wall.
At one end of a dark room erect a screen that shall conceal you and your apparatus effectually from the spectators. Upon a table behind this screen place a large mirror, such as can be found upon any dressing-table. Put a lighted candle in front of this glass, placing the latter at such an angle that a large patch of light is thrown upon the wall before you, as in Fig. 1.
The screen must, of course, hide all this from the company, who will see nothing but the light on the wall.
To write your message is now a very simple matter. Dip a coarse brush into some lamp-black water color, and, writing backwards, inscribe what you wish upon the face of the mirror. The message will then appear legibly upon the wall, seemingly written by a mysterious hand.
By dipping the brush into clean water and washing out what you have written upon the glass, the message on the wall will disappear as inexplicably as it appeared in the first place.
Fig. 2.—Thread passed round prongs of the bone.
Fig. 3.—Match through twisted thread.
A peculiar optical illusion is accomplished as follows. The wishbone of a fowl or duck should be thoroughly cleaned, and a thread passed several times around the prongs of the fork, as shown in Fig. 2. Having secured the thread tightly, pass a strong wooden match between the strands, twisting it several times until the prongs of the bone have been drawn closer together (Fig. 3).
Now, pulling out the match sufficiently to allow of one end catching against the fork, hold the bone firmly. Releasing the match it immediately describes a circle, striking against the under part of the fork, but so rapidly has it completed this revolution that the eye has been quite unable to follow it. This causes an illusion that induces all who witness the experiment to imagine that the match passes through the fork of the bone at A.
But if the eye was too slow in the last experiment, it is so officious in what is next to be described that it sees something which really does not take place.
Fig. 4.—The lion and his cage.
Draw a lion and a cage, as in Fig. 4. If you place a visiting card upon the line A B, and put your face so near that the right eye looks upon the lion whilst the left can see only the cage, you will observe the lion walking into his cage as naturally as if he were at the Zoo!
A rather amusing experiment, and one which will afford immense pleasure to the juvenile members of your party, is as follows:—
Cut a circular disc of stout cardboard 12″ in diameter. In the center make a hole to allow the disc to revolve easily, but not loosely, upon a wooden penholder, which should be fixed at right angles to a wooden stick (Fig. 5).
Fig. 5.—Disc of cardboard kept in place with penholder.
Fig. 6.—Showing box in correct position.
Upon the center of the disc fasten a cylindrical cardboard box (A, Fig. 6), with the penholder passing right through it. This box should be roughly 3″ high and 2″ in diameter.
At a radius of 41⁄2″ from the center describe a semicircle upon the disc at E F (Fig. 6), whilst upon the same half of the cylinder describe a line as G H in the same figure. Now pierce about twenty-five equidistant holes in E F and G H, joining them with thread, as in Fig. 7.
Cover these threads with little strips of paper in such a manner as to make a plane surface, as shown in Fig. 8. Then fasten a cork upon the end of a wire attached to the stick, and in a cleft in this cork put a little cardboard figure as in the illustration.
Make the disc revolve by a rapid turn of the hand, and if a candle be so placed as to cast the shadow of the little man upon the disc, he will be seen engaged in making sundry passes and lunges in the manner of the perfect fencer.
Fig. 7.—Mode of joining thread.
Fig. 8.—The toy complete.
Various other figures can be made in a similar way with great success, and when cleverly managed the toy will be found most amusing.
Life Partners
If at any time it should happen that an engaged couple are amongst the friends whom you wish to entertain, a very simple piece of apparatus can be made that will give these good people much pleasure.
In the four sides of a cube box, measuring 18″ each way, make an oval opening, 9″ by 7″, as A, B, C, D in Fig. 9. Inside the box place two mirrors, back to back, diagonally from G to E (Fig. 10), and contrive four curtains to draw up simultaneously over the holes.
Fig. 9.—Showing box with oval openings.
Fig. 10.—Showing box with oval openings and mirrors.
You must now get two couples to look through the holes, arranging the two men opposite each other, as at A and C, and the ladies at B and D, promising them that by looking into the simple but magical box they shall see the future partners of their lives and pleasures.
As soon as they are in position raise the curtains, when A will see B, and C will be gazing at D, so that if you have sorted the parties aright, they will feel so pleased with themselves and with you that no inquiry will be made as to how the trick is done.
To turn from sight to hearing, the following is a simple experiment which can be exhibited without any special apparatus.
Cut a plain cross from a sheet of notepaper, as in Fig. 11, and place it over a wine-glass, bending the ends to prevent it slipping off. Almost fill the glass with water, taking great care to leave the sides and rim perfectly dry.
If you damp your finger and pass it over any part of the glass outside, a distinct humming will be heard, but the more remarkable thing to observe is that the cross will begin to revolve very slowly so long as your finger rubs a portion of the glass between the arms of the cross—as at A in Fig. 11. Yet when you begin to rub beneath one of the arms the paper will remain perfectly still. A complete revolution of the paper can be produced by rubbing round the glass in a circle.