Part 30
This _self-upholding_ property constitutes the wonder and puzzle of the instrument, and many explanations have been attempted. Some ascribe it to atmospheric influence; others to electricity; while others confidently remark, "Ah, yes, I understand it--it is the _motion_ which keeps it from falling--it is the momentum--the centrifugal force;" but _why_ this result is produced by centrifugal force, we are not told.
The true explanation is this:
1. The wheel when at rest, may of course be easily moved about so as to alter the position of its axis, in any direction. But this is not so when it is made to spin rapidly; if the ring is held in the hands, the wheel will be found strongly to resist any side or twisting movement--so much so, that a novice will start, and almost let it drop, supposing there is something _alive_ in it or, as they sometimes remark; "Why! it feels as if there was a _snake_ in the wheel!" This is owing to nothing but the strong momentum of the _lead rim_ (already described) tending to keep the wheel in its position; for an attempt to alter its position, throws all this swiftly flying matter into a different course, which, it is evident, cannot easily be done.
2. The _slowly revolving_, horizontal motion on the pivot at A is in a contrary direction to the _spinning_ motion of the _top_ of the wheel, as the arrows show in Fig. 1. In other words, the forward portion of the wheel flies upwards, and the back portion downwards. This will be found to be always the case.
3. Now, when the wheel is moving on horizontally around the pivot at _a_, the forward portion of the rim is continually moving to the _left_, and the hinder portion to the right, as represented in Fig. 2. The combined motion of the forward part of the wheel both upward and to the left, is therefore not perpendicularly upward, but inclined to the left, and the tendency of its momentum is to throw the top of the wheel also to the left. In the same way, the downward momentum behind throws the bottom to the right. Throwing the top to the left and the bottom to the right, of course raises the wheel as it rests on the pivot A. In other words, the combined motion of the wheel on its axis, and on the pivot A, constantly tends to raise it, thus overcoming gravity, and maintaining the wheel in its position, supported only at one end.
4. The momentum of the lead rim, as described in (1.) tending to keep the wheel in its position, keeps it also in a uniformly horizontal attitude; if placed by the hand, inclining upwards, it will move around on the pivot at _a_, without altering this inclination; or the same result takes place, if inclined below the horizontal.
5. The reason of the forward horizontal movement, is this: the spinning force of the wheel tends to throw it to the left, and consequently to lift it upwards, as shown in (3.)--gravity, on the opposite hand, tends to draw it downward; the _resultant_ (or mid-way) motion is therefore between them, or horzontally. As a proof that gravity thus produces the onward movement--when the wheel spins with the greatest rapidity, and consequently has the greatest relative force to gravity, the horizontal movement is slowest; but it continues constantly to increase as the motion of the wheel is retarded, and as gravity assumes a greater proportionate force.
THE ARTIFICIAL LANDSCAPE.
Procure a box, as in cut, 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-glass, that shall exactly fit; but at that end where the sight hole A is, scrape the quicksilver off the glass, through which the eye can view the objects.
Cover the box with gauze, over which place a piece of transparent glass, 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 skillfully painted, on both sides, any subject you think proper, as woods, bowers, gardens, houses, &c.; and on two other boards, the same subject 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.
EASY AND CURIOUS METHODS OF FORETELLING RAINY OR FINE WEATHER.
If a line be made of good whipcord, that is well dried, and a plummet affixed to the end of it, and then hung against a wainscot, and a line drawn under it, exactly where the plummet reaches, in very moderate weather it will be found to rise above it before rain, and to sink below when the weather is likely to become fair. But the best instrument of all, is a good pair of scales, in one of which let there be a brass weight of a pound, and in the other a pound of salt, or of saltpeter, well dried; a stand being placed under the scale so as to hinder it falling to low. When it is inclined to rain, the salt will swell, and sink the scale: when the weather is growing fair, the brass weight will regain its ascendancy.
Another very simple method is, to take a strip of pine wood, about twenty inches long, one wide, and a quarter thick, and cut across the grain. Then take a strip of cedar, of the same dimensions, but cut along the grain. Glue them firmly face to face, and set them upright in a stand. Some time before rain falls, the pores of the pine will absorb moisture from the atmosphere, and swell until the whole forms a bow, which will straighten itself as fine weather approaches. It is needless to say that the rods should not be painted or varnished.
THE MAGICAL MEASURE.
The line to be measured must not be extravagantly long, otherwise it will be difficult to measure it accurately; for the least failure of a just aim, or departure from an upright position, would make very sensible errors in the measure of a very long line, especially if the ground was very uneven. To measure then the line A B, accessible at the extremity A, suppose the breadth of a small river, he who pretends to measure must stand very straight at the extremity A, and support his chin with a little stick resting upon one of the buttons of his coat, so as to keep his head steady in one position. He must pull his hat down upon his forehead till the brim of his hat covers from his view the inaccessible extremity B of the line to be measured A B, then he must turn himself to a level, uniform piece of ground, and with the same position of his hat, observe the point of the ground where his view terminates, as C, then measuring with a line or chain the distance A C, he has the length of the line proposed A B.
THE BOUNDLESS PROSPECT.
Take a square box, about six inches long and twelve high, or of any other proportionate dimensions. Cover the inside with four flat pieces of looking glass placed perpendicular to the bottom of the box. Place at the bottom any objects you please, as a piece of fortification, a castle, tents, soldiers, &c. On the top, place a frame of glass shaped like the bottom of a pyramid, as in the figure, and so formed as to fit on the box like a cover. The four sides of this cover are to be composed of ground glass, or covered inside with gauze, so that the light may enter, and yet the inside be invisible, except at the top, which must be covered with transparent glass: when you look through this glass, the inside will present a pleasing prospect of a boundless extent; and, if managed with care, will afford a deal of amusement.
THE HOUR OF THE DAY OR NIGHT TOLD BY A SUSPENDED SHILLING.
However improbable the following experiment may appear, it has been proved by repeated trials:
Sling a shilling or sixpence at the end of a piece of thread by means of a loop. Then resting your elbow on a table, hold the other end of the thread betwixt your fore finger and thumb, observing to let it pass across the ball of the thumb, and thus suspend the shilling into an empty goblet. Observe, your hand must be perfectly steady; and if you find it difficult to keep it in an immovable posture, it is useless to attempt the experiment. Premising, however, that the shilling is properly suspended, you will observe, that when it has recovered its equilibrium, it will for a moment be stationary: it will then of its own accord, and without the least agency from the person holding it, assume the action of a pendulum, vibrating from side to side of the glass, and, after a few seconds, will strike the hour nearest to the time of day; for instance, if the time be twenty-five minutes past six, it will strike six; if thirty-five minutes past six, it will strike seven; and so on of any other hour.
It is necessary to observe, that the thread should lie over the pulse of the thumb, and this may in some measure account for the _vibration_ of the shilling; but to what cause its striking the precise hour is to be traced, remains unexplained; for it is no less astonishing than true, that when it has struck the proper number, its vibration ceases, it acquires a kind of rotary motion, and at last becomes stationary, as before.
CONTRIVANCE FOR A WATCH LAMP, PERFECTLY SAFE, WHICH WILL SHOW THE HOUR OF THE NIGHT, WITHOUT ANY TROUBLE, TO A PERSON LYING IN BED.
It consists of a stand, with three claws, the pillar of which is made hollow, for the purpose of receiving a water candlestick of an inch diameter. On the top of the pillar, by means of two hinges and a bolt, is fixed on a small proportionate table, a box of six sides, lined with brass, tin, or any shining metal, nine inches deep, and six inches in diameter. In the center of one of these sides is fixed a lens, double convex, of at least three inches and a half diameter. The center of the side directly opposite to the lens is perforated so as to receive the dial-plate of the watch, the body of which is confined on the outside, by means of a hollow slide. When the box is lighted by a common watch-light, the figures are magnified nearly to the size of those of an ordinary clock.
THE ENCHANTED PALACE.
On the six-sided plane A B C D E F of the figure, draw six semi-diameters; and on each of these place perpendicularly two plane mirrors, which must join exactly at the center, and which, placed back to back, must be thin as possible. Decorate the exterior boundary of this piece, (which is at the extremity of the angles of the hexagon,) with six columns, that at the same time serve to support the mirrors by grooves formed on their inner sides. Add to these columns their entablatures, and cover the edifice in whatever manner you please. In each one of these six triangular spaces, contained between two mirrors, place little figures of pasteboard, in relief, representing such subjects, as when seen in an hexagonal form, will produce an agreeable effect. To these add small figures of enamel, and take particular care to conceal by some object that has no relation to the subject, the place where the mirrors join, which, as before observed, all meet in the common center.
When you look into any one of the six openings of this palace, the objects there contained, being reflected six times, will seem entirely to fill up the whole of the building. This illusion will appear very remarkable, especially if the objects chosen are properly adapted to the effect which the mirrors are intended to produce.
If you place between two of these mirrors part of a fortification, as a curtain, and two demi-bastions, you will see an entire citadel with six bastions; or if you place part of a ball-room, ornamented with chandeliers and figures, all these objects being here multiplied, will afford a very pleasing prospect.
TO KNOW WHICH OF TWO DIFFERENT WATERS IS THE LIGHTEST WITHOUT ANY SCALES.
Take a solid body, the specific gravity of which is less than that of water, pine, or fir wood, for instance, and put it into each of the two waters, and rest assured that it will sink deeper in the lighter than in the heavier water; and so by observing the difference of the sinking, you will know which is the lightest water, and consequently the most wholesome for drinking.
TO KNOW IF A SUSPICIOUS PIECE OF MONEY IS GOOD OR BAD.
If it be a piece of silver that is not very thick, as a dollar or a half dollar, the goodness of which you want to try, take another piece of good silver of equal balance with it, and tie both pieces with thread or horse-hair to the scales of an exact balance (to avoid the wetting of the scales themselves) and dip the two pieces thus tied in water; for then, if they are of equal goodness, that is, of equal purity, they will hang in equilibrio in the water as well as in the air; but if the piece in question is lighter in the water than the other, it is certainly false, that is, there is some other metal mixed with it that has less specific gravity than silver, such as copper. If it is heavier than the other, it is likewise bad, as being mixed with a metal of greater specific gravity than silver, such as lead.
If the piece proposed is very thick, such as that crown of gold that Hiero, king of Syracuse, sent to Archimedes to know if the goldsmith had put into it all the eighteen pounds of gold that he had given him for that end, take a piece of pure gold of equal weight with the crown proposed, viz., eighteen pounds, and without taking the trouble of weighing them in water, put them into a vessel full of water, one after another, and that which drives out most water must necessarily be mixed with another metal of less specific gravity than gold, as taking up more space, though of equal weight.
PYRAMID OF ALUM.
Put a lump of alum into a tumbler of water, and as the alum dissolves it will assume the shape of a pyramid. The cause of the alum decreasing in this peculiar form is briefly as follows: at first, the water dissolves the alum very fast, but as the alum becomes united with the water, the solvent power of the latter diminishes. The water, which combines first with the alum, becomes heavier by the union, and falls to the bottom of the glass, where it ceases to dissolve any more, although the water which it has displaced from the bottom has risen to the top of the glass, and is there acting upon the alum. When the solution has nearly terminated, if you closely examine the lump, you will find it covered with geometrical figures, cut out, as it were, in relief upon the mass; showing, not only that the cohesion of the atoms of the alum resists the power of solution in the water, but that, in the present instance, it resists it more in some directions than in others. Indeed, this experiment beautifully illustrates the opposite action of cohesion and solution.
THE DANCING AUTOMATON.
Procure a piece of silk thread about six feet long, and fasten a small wire hook at one end, and a fine needle at the other, then make a knot in the thread about ten inches from the end upon which the hook is fastened. You also procure a small pasteboard figure about four inches long, and pierce a hole through the center of the same just large enough to easily admit the needle. Having done this, take a convenient opportunity and fasten the hook in the carpet about five and a half feet from the chair upon which you intend to sit while performing the trick. You then can inform your audience that you intend to make the figure dance and keep time to any tune they may name. You then slip the needle through the hole in the figure and throw it down on the floor, with sufficient force to make it slip on the thread until it reaches the knot, being careful to retain the needle still in your hand, then whistle any air the company may suggest, and appear to beat time with your hands upon your knees. This will make the figure dance, to the great astonishment of the spectators. After you have continued this for a few minutes, you must drop the needle and pick up the figure, when the needle will again slide through the hole in the figure, and the automaton being free from the thread, you can hand it to the audience for examination. This is an excellent trick for the parlor, and, if well performed, will defy detection.
TO MELT A PIECE OF MONEY IN A WALNUT SHELL, WITHOUT INJURING THE SHELL.
Bend any thin coin, and put it into half a walnut shell; place the shell on a little sand, to keep it steady. Then fill the shell with a mixture made of three parts of very dry pounded niter, one part of flowers of sulphur, and a little sawdust well sifted. If you then set light to the mixture, you will find, when it is melted, that the metal will also be melted at the bottom of the shell, in form of a button, which will become hard when the burning matter round it is consumed: the shell will have sustained very little injury.
THE INVISIBLE SPRINGS.
Take two pieces of white cotton _cord_, precisely alike in length; double each of them separately, so that their ends meet; then tie them together very neatly, with a bit of fine cotton _thread_, at the part where they double (_i. e._ the middle). This must all be done beforehand. When you are going to exhibit the trick, hand round two other pieces of cord, exactly similar in length and appearance to those which you have prepared, but not tied, and desire your company to examine them. You then return to your table, placing these cords at the edge, so that they fall (apparently accidentally) to the ground, behind the table; stoop to pick them up, but take up the prepared ones instead, which you had previously placed there, and lay _them_ on the table. You then take round for examination three ivory rings; those given to children when teething, and which may be had at any of the toyshops, are the best for your purpose. When the rings have undergone a sufficient scrutiny, pass the prepared double cords through them, and give the two ends of one cord to one person to hold, and the two ends of the other to another. Do not let them pull hard, or the thread will break, and your trick be discovered. Request the two persons to approach each other, and desire each to give you one end of the cord which he holds, leaving to him the choice.
You then say that, to make all fast, you will tie these two ends together, which you do, bringing the knot down so as to touch the rings; and returning to each person the end of the cord next to him, you state that this trick is performed by the rule of contrary, and that when you desire them to pull hard, they are to slacken, and _vice versa_, which is likely to create much laughter, as they are certain to make many mistakes at first. During this time you are holding the rings on the fore fingers of each hand, and with the other fingers preventing your assistants from separating the cords prematurely, during their mistakes; you at length desire them, in a loud voice, to slack, when they will pull hard, which will break the thread, the rings remaining in your hands, whilst the strings will remain unbroken: let them be again examined, and desire them to look for the springs in the rings.
THE FLIGHT OF THE RING.
You may cause a ring to shift from one hand to another and make it go on any finger required on the other hand, while somebody holds both your arms, in order to prevent communication between them, by attending to these instructions: Desire some lady in company to lend you a gold ring, recommending her at the same time to make a mark on it, that she may know it again. Have a gold ring of your own. which fasten by a small piece of catgut string to a watch barrel, and sew it to the left sleeve of your coat. Take the ring that is given you in your right hand; then putting, with dexterity, the other ring fastened to the watch-barrel near the entrance of your sleeve, draw it privately to the fingers' ends of your left hand. During this operation, hide the ring that has been lent you between the fingers of your right hand, and fasten it dexterously on a little hook sewed for the purpose, on your waistcoat, and hidden by your coat. After that, show your ring, which hold in your left hand; then ask the company on which finger of the other hand they wish it to pass. During this interval, and as soon as the answer has been given, put the before mentioned finger on the little hook, in order to slip the ring on it: at that moment let go the other ring, by opening your fingers. The spring which is in the watch-barrel, being confined no longer, will contract, and make the ring slip under the sleeve, without any body perceiving it, not even those who hold your arms, as their attention will be occupied to prevent your hands from communicating. After this operation, show the assembly that the ring is come on the other hand, and make them remark that it is the same that had been lent to you, or that the mark is right. Much dexterity is required in this trick, so that the deception may not be suspected.
MUSICAL FIGURES RESULTING FROM SOUND.
Cover the mouth of a wine glass, having a foot-stalk, with a thin sheet of membrane, over which scatter a layer of fine sand. The vibrations excited in the air by the sound of a musical instrument, held within a few inches of the membrane, will cause the sand on its surface to form regular lines and figures with astonishing celerity, which vary with the sound produced.
TO MAKE A CARD JUMP OUT OF THE PACK.
Let any person draw a card, and afterwards put it into the pack, but take care that you know where to find it at pleasure. This you may do by having _forced_ it. Then put a piece of wax under the thumb-nail of your right hand, and fasten a hair by it to your thumb, and the other end of the hair, by the same means, to the card chosen: spread the pack upon the table, and, making use of any words you think fit, make it jump from the pack about the table.
THE TELL-TALE CARDS.
Tell any one to shuffle the pack, to take off the upper card, and to notice it, then to lay it on the table, with its face downward, and put so many cards upon it as will make up thirteen with the number of spots on the noted card.
For instance: if the card which the person first looked at was a king, queen, knave, or ten, bid him lay that card with its face downward, calling it ten; upon that let him lay another, calling it eleven; upon that, another, calling it twelve; and upon that, another, calling it thirteen; then bid him take off the next uppermost card: suppose it to be an eight, let him lay it down on another part of the table, calling it eight; upon the latter another, calling it nine, and so on in the same way, until he makes that heap up to thirteen; then let him go to the next uppermost card, and so proceed to lay out the third parcel in the same way as the two preceding, and should the uppermost card be an ace, he must lay it down, calling it one, the next two, &c.