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The Table of Contents was created by the transcriber and placed in the public domain.

[Additional Transcriber’s Notes] are at the end.

CONTENTS

[The Pile of Draughtsmen.]
[The Decanter, Card, and Coin.]
[A Clever Blow.]
[The Obedient Coin.]
[To Cut a String With Your Hands.]
[The Rebound.]
[A Fiery Catapult.]
[To Make an Exact Balance.]
[The Recomposition of Light.]
[The Mysterious Apple.]
[Economical Letter-Scales.]
[Tracing a Spiral.]
[The Inclined Plane.]
[To Cut a Bottle With a String.]
[Equilibrium of a Knife in Mid-Air.]
[A Trick With Four Matches.]
[The Distance of an Inaccessible Point.]
[Practical Tracing of a Meridian Line.]
[To Measure the Height of a Mountain.]
[To Take Up Four Knives with One.]
[The Tack in the Ceiling.]
[The Jumping Pea.]
[To Acquire a True Eye.]
[The Air-Tight Stopper.]
[The Fusee Rocket.]
[A Novel Table Mat.]
[Geometrical Paper Band.]
[Photographic Camera.]
[The Phantom Needle.]
[Amphitrite.]
[Optical Illusions.]
[The Insensible Coin.]
[The Asses’ Bridge.]
[Another Way to Prove the Preceding Theorem.]
[Indented Angles.]
[A Cheap Shooting Gallery.]
[The Coin in Equilibrium.]
[The Submerged Coin.]
[The Smoke Rings.]
[The Walking Cork.]
[The Obstinate Cork.]
[Petroleum Pulverizer.]
[Electric Attraction and Repulsion.]
[The Bust of the Sage.]
[The Witchery of the Hand.]
[The Perspectograph.]
[Camphor in Water.]
[A Simple Multiplier.]
[The Drawing Room Mirror.]
[Elementary Gas-Burner.]
[Rapid Vegetation.]
[Miniature Volcanoes.]

HOW TO DO
MECHANICAL TRICKS.

Containing complete instruction for
performing over sixty ingenious
Mechanical Tricks.

By A. ANDERSON.

FULLY ILLUSTRATED.

New York:
FRANK TOUSEY, Publisher,
24 Union Square.

Entered according to Act of Congress, in the year 1902, by

FRANK TOUSEY,

in the Office of the Librarian of Congress at Washington, D. C.

HOW TO DO
MECHANICAL TRICKS.

The Pile of Draughtsmen.

“Matter is inert.” That is what you read in every treatise on physics—what does it mean? Here is a very simple experiment that will prove this truth to anyone.

Pile up ten draughtsmen, as shown in [Fig. 1]. Before this pile place another piece on edge, and pressing its circumference with the forefinger, let it glide from underneath so that it strikes the pile with considerable force. The piece so thrown must, you will think, upset the whole pile of draughts; but no: the piece thus sharply sent forward will strike only one piece of the pile, and this alone will be dislodged without putting the others out of their equilibrium, and the whole column above will settle down together on the bottom piece.

Fig. 1.

In effect, the force of the impulse, making itself felt on the piece that is touched, the latter leaves the pile without transmitting its movement to the other pieces, which, following another physical law, that of gravity, descend vertically to fill the place left vacant.

The experiment may be varied by using a knife and striking with it a sharp horizontal blow on one of the pieces. The piece struck will fall out of the pile without disturbing the symmetry of the others.

The Decanter, Card, and Coin.

This law of “Inertia” will provide us with a few more experiments as curious as they are conclusive.

Place a playing or an ordinary visiting card on a decanter; upon the card and just in the center, over the aperture of the decanter, put a small coin (a dime). Now, if with a sharp fillip, given horizontally on the edge of the card, you succeed in whisking it off (which is very easy), the coin will fall to the bottom of the decanter. The following phenomenon has taken place: the movement was too rapid to be transmitted to the coin, and the card alone was whisked off.

The coin being no longer sustained by the card falls, of course, vertically, without having in the least come out of position.

A sharp horizontal knock given with a penholder or small stick on the edge of the card, will produce the same result, but the fillip is more effective.

A Clever Blow.

Take a thin stick about a yard long, and thrust a pin firmly in each of its extremities. This done, place the stick on the bowls of two pipes, which a couple of persons hold by the stems, in such a manner that the pins only rest on the pipes. A third person then strikes the stick sharply in the middle, and it will break without injuring the pipes.

Ordinary clay pipes will do very well, as the more brittle the pipes are, the more striking is the experiment. How is this explained?

The mechanical effect of the shock has not time to reach the bowls of the pipes (inertia), and is only manifested at the very point on which the blow falls, hence the stick unable to resist the force of the blow at the one point breaks in two pieces.

The Obedient Coin.

Take an ordinary wooden matchbox, and remove the drawer holding the matches. In the center place a small coin, a cent will be the best for the experiment, the object of which is to make the coin fall into the interior without touching it. Tap lightly on that side of the box to which you desire the coin to come, until it rests upon the edge.

Then slightly raise the end of the box whereon the coin rests, and lightly tap with the finger once more. At once the coin will fall into the box. The secret of the experiment is this: the taps on the box only move the box, while the coin retains its position by reason of its own inertia, until the edge of the box reaches it. The last tap knocks away the support, and the coin, obedient to the law of gravity, falls vertically into the interior of the box. This little experiment is easily performed, and extremely interesting when done neatly.

To Cut a String With Your Hands.

With a little practice, and some briskness of movement, you may be able to break a string of considerable thickness by proceeding as follows:

Wind the string round your left hand, so as to make a loop, as shown in the figure. Pass it three or four times round the fingers to insure the solidity of the loop. Seize firmly the other end of the string with your right hand, around which you wind it three or four times, then give a brisk pull. The string will be clean cut at the junction of the loop in the left hand.

When the knack is well acquired, one may break the string on two fingers only, by following always the same theory as above.

The Rebound.

On the neck of a bottle place a cork in an upright position. The cork must be large enough to rest on the neck without falling in.

Now give a sharp fillip on the neck of the bottle, and you will see the cork fall, not on the other side of the bottle as most people expect, but forward in the direction of the hand giving the blow. This, again, is an illustration of the principle of inertia. A rapid blow tends to push the bottle from the cork before the movement is transmitted to the latter.

Few people will execute this experiment properly the first time, for the instinctive fear to break the bottle and cut their fingers, will prevent them giving a blow sharp enough to make this experiment successfully at the first attempt; but with a little perseverance, the necessary degree of force will be gauged to a nicety.

A Fiery Catapult.

Take a match-box and place it upright edge-wise and place two matches in each side between the inner and outer box, heads up. They must be inserted deeply enough to stick firmly.

Place a third match cross-wise between them and it will stay there by the pressure the latter exercises on them.

Now light the middle of the horizontal match and wait. What do you think will happen? Ask the bystanders which will first catch fire?

The natural conclusion they will draw will be the following.

From the middle the frame will spread of course to the two extremities and light the other two matches, probably this side first where the two phosphorous heads meet.

Well, nothing of the sort happens. When the volume of the burning match has diminished, and consequently its rigidity also, the force of its resistance grows weaker as the combustion proceeds.

A moment comes when the two vertical matches, trying to assume again their original position, throw off, with a sway, the burning horizontal match.

The burning match was rendered flexible in the middle, and is not at all burned at the ends, and the two matches remain standing as before.

To Make an Exact Balance.

To construct by yourselves, with the help of simple materials a balance of great precision may seem impossible. Nevertheless it can be done.

A ruler, a tin box, (in which blacking was contained, for example) three blocks of wood, two pins, thread, four nails, a small piece of glass, and cardboard are all the necessary materials, and now to work.

At a short distance from the center of the ruler, and on a cross line with one another, stick two pins so that they come out a little on the other side. At one end of the ruler, in C, nail a small piece of your box.

At the spot, where the hook to which the scale is suspended, is to hang, make an indentation with the point of a nail, so that the hook does not shift at the other extremity, in A, fasten a flat piece of tin, which will form one of the scales of your balance.

At the end of this pan solder a pin point downwards. Your second scale, B, destined to contain the object or substances to be weighed, will be formed by the lid of the blacking-tin.

On its rim at nearly equal distances pierce four holes, on which the suspension-strings will be tied, the latter at their upper end being united together in one string, which is tied to a hook (a bent pin or fishing hook will do.)

Now the point of support remains to be constructed. On a wooden square, rather thick, E, fix another block, G, on which gum a piece of glass. In the largest block knock four nails to prevent the shaft of the balance swerving from right to left.

The small truncated pyramid, D, which you perceive on the left of the design, and which is graduated, serves as bench-mark.

In order to weigh you use the method due to Borda, called the method of double weights.

Place in the scale A a weight which you think is slightly over the one of the substance or object to be weighed. Then the scale B being occupied, get equilibrium by shifting more or less towards the ruler, the weight on the scale A.

Then note the division indicated by the pin point, and take from scale B the article placed there, and put therein weights until the point of scale A tells you that the equilibrium is the same as when the substance was in the scale.

It is not necessary that this balance be exact, provided it answers the very small differences in the pans.

The one we have indicated will weigh down to a fifty-thousandth part of a pound.

The Recomposition of Light.

It is a great pity that exquisitely beautiful facts and mysteries are wrapped up in the crack-jaw terms of foreign languages, and so made to appear ugly.

There is no branch of knowledge more fascinating than light. To follow up its study is like walking along a shady lane, where at certain distances apart the wayfarer lights upon jewels of great brilliance.

It has been said above that white light is formed by the union or combination of seven colors. When a ray of light passes through a prism it is split up into the parts of which it is composed, and seven colors as in the rainbow appear.

These colors shade off into one another with every variety of tint, like a band of rainbow-colored ribbon. This band is called a spectrum.

Now, where science classes are held there may be seen a complicated instrument, which is used to show how the seven colors unite to form white light. It is a disc on which the colors of the spectrum are painted, and it is made to spin round with great rapidity.

The impression received by the eye, when looking at the revolving disc is total abstinence of color. In other words it is white light.

Fortunately, you can satisfy yourselves on this point without any other materials than a cardboard disc and a piece of string. On this disc paint in small sections the colors of the spectrum, repeating them four or five times in the following order: red, orange, yellow, green, blue, indigo, violet.

That the experiment may be entirely successful, the sections must be marked off according to the following scale of width of section. Let orange, next to the circumference represent 2: then

Now, in any diameter of the disc bore two holes not too near the edge. Through them pass a piece of string, and knot the two ends together. Take hold of the string with both hands, and make the disc spin round.

Then extend and approach the hands alternately to give a very rapid movement to the disc. When revolving rapidly enough you will not be able to distinguish the separate colors. They all become blended into white light.

The Mysterious Apple.

Pierce an apple in such a manner as to obtain two holes tending toward the middle, and forming a pretty large angle as shown in the figure. Two quills or tin tubes should be inserted to make the inside passages smooth. Pass a string through the hole and your apple is prepared for a little trick, which, you may be sure will astonish all persons before whom you practice it, and who of course are not yet initiated.

You fasten one extremity of the string to your foot, and take the other in your hand so as to produce at will the rigidity of the string. You can then command the apple to go down, or to stop, and it will obey your order immediately. Indeed, when you straighten the string, the part which enters the apple pushes against the angle formed by the two passages, and by the pressure, holds the apple. When on the contrary you let go a little, you take away the rigidity and the apple glides down.

You can therefore alternately let the apple go down or stop its course, and we repeat it, persons not in the secret cannot imagine by what means you get this curious result.

If, instead of an apple one takes a wooden ball, the experiment will be more interesting and the article will last longer.

Economical Letter-Scales.

Take a watch or small clock spring, and fix it by the center on a stick. At the other end attach a small brass hook to hold letters, etc., as shown in the figure.

At the top of the hook fix horizontally a small band, running over a strip of cardboard, likewise hanging on the stick.

Now graduate the cardboard strip with real weights, or their exact equivalents, and after this any small articles may be weighed with sufficient accuracy. The spring, being of steel, always turns to its original position when the scale is empty.

Tracing a Spiral.

In geometry the process for tracing a spiral by the help of compasses is pretty long and tedious. The following method will enable you to do it far more quickly and as accurately.

Take a wooden or cardboard cylinder, with a diameter equal to a fourth part of the distance you require between the spires (or trelices) to be traced. On this cylinder fasten one end of a string, B, and wind it up, and attach to the other end a pencil, C, or a point, according to what you want to do.

Now you have only to turn to right or left according to the direction in which the string was wound up, by holding the pencil down and keeping the string tight, and a spiral of perfect regularity will be traced.

The above figure clearly shows the process. The cylinder A has a diameter equal to the distance R S divided by 4.

The Inclined Plane.

Take a piece of paper, roll it up into a tube large enough to hold a marble, and gum it lengthwise. Then introduce a marble and close the extremities with a strip of paper as shown below.

When you think that it is well dried you place it upright on the upper end of an inclined board, or flat ruler, leaning on a pile of books for example. You will then see the paper cylinder lie down, get up and so on till it reaches the bottom of its course.

The effect is very curious and will be more so if you are somewhat of an artist, and able to draw or paint a figure on the cylinder.

To Cut a Bottle With a String.

Gum first two circular pads of paper on each side of the spot where you intend to cut your bottle. These pads are obtained by gumming several strips of paper one over the other, so as to leave between them a groove on which you wind the string round once.

Catch hold of the extremities of the string, and draw it to and fro, see-saw fashion, by which friction the part of the glass operated on will be heated.

As soon as you think that the glass is hot enough, plunge the bottle in cold water, which you will have placed handy before, and at the spot where the friction was exercised the glass will be clean cut. According to the thickness of the glass, more or less heat must be produced. This process is infallible.

The same result can also be produced in another way. It is, when once the heat is sufficient to let glide a few drops of water along the string. The string must be well wetted. The cut will be as clean as by the other process.

Equilibrium of a Knife in Mid-Air.

Be reassured dear readers, we are not going to ask you to make a balance in mid air, that would be too much for our weak capabilities. The question is simply to swing a knife horizontally in the space which surrounds us. The experiment is curious and easily executed.

Take the cork of a champagne bottle. Pierce it lengthwise with a sharp knife, and let the knife stick out a third of its length from the thin end of the cork. Then insert into each side of the cork the prongs of two forks, so that they are perpendicular with the blade of the knife as shown in figure.

This operation accomplished, you have only to suspend the point of the blade on the loop of a string, and the knife will hang horizontally. You may then swing it if you choose, and the movement will not destroy the equilibrium.

A Trick With Four Matches.

Speaking of matches, there is yet one more trick to be played with four of them.

At the non-phosphoric ends of two matches cut a small notch so that they fit into each other. Stretch the matches apart so as to form an angle, and place them vertically upon the table. Then lean a third match against them so as to form a tripod, standing by itself.

The question now is to take up this trivet with a fourth match and carry it to another place without disturbing the harmony of the little construction.

At first sight this seems impossible; it is, however, easily done. You have only to slide the fourth match between the two stuck together, and the one serving as support.

By lightly pressing against the two first ones the third one will slide, and its upper extremity will come between the angle formed by the two others. By taking it up briskly, this extremity will be maintained, and you are then enabled to carry the little tripod to another place.

The Distance of an Inaccessible Point.

Everyone knows what an angle is, and you say at once it is the inclination of two lines that meet each other. These lines by their branching off form an opening more or less wide. This opening is measured by the aid of an instrument called a protractor made of brass or horn, which finds its place in nearly every box of mathematical instruments.

It represents a semi-circumference, divided into 180 equal parts, called degrees, written thus: 180°. Each degree is divided into 60 minutes, expressed thus: 60 min.; and finally the minutes are divided again in 60 parts, called seconds, indicated thus: 60 sec. There are therefore in a whole circumference, 360 deg., 2,160 min., and 12,960 sec.

One degree, therefore, is the 360th part of a circumference, and thus we have a measure independent of all dimensions. For example, on a round table of 36 yards in circumference, one degree will be marked by one tenth of a yard; on a pond of 360 yards in circumference, one degree will be equal to one yard.

The degree, therefore, may be more or less, but it is always the 360th part of the circumference of a circle. Let it be quite understood that, whether an angle is to be on a sheet of paper, or in the skies, the divisions do not change.

This must be well grasped, it is of the utmost importance for the explanations which follow. It is therefore settled: the measure of the angles has nothing to do whatever with a measure of length.

We have shown how to measure an angle. Let us examine now what is a triangle, without pondering too much over this geometrical figure, which every one knows. The essential property of this three-cornered figure is that the sum of its three angles is always equal to 180 degrees.

In other words, the protractor placed successively at each angle will give three numbers, which, added, make up 180 degrees. Keep this property well in mind, as it will serve us hereafter.

Now, to what distance does a degree correspond? For example, take a yardstick, and with the graphometer (an instrument by which angles are measured), in readiness, carry it from the latter instrument to a certain distance, till the two extremities of the yardstick measure one degree; this yard is then said to subtend an angle of one degree.

Now, measure the distance which divides the yardstick from the instrument, and you will find it to be 57 yards. Therefore, one degree corresponds to an object being at a distance of 57 times its height. A man two yards high at a distance of 57 times his height, or 114 yards will measure one degree.

One minute will be represented by a piece of cardboard of a hundreth part of a yard long seen from a distance of 34 yards; and finally, a second will be given by a card a hundreth part of a yard seen from a distance of 2062 yards.

A hair seen at 20 yards about represents a second. This perhaps, you think to be too small to be seen by the naked eye.

Suppose that you to measure the distance of a church situated on a height, and from which you are separated by a river (see fig.) Choose on the river’s bank two spots from which the steeple C can be seen, say A and B. At B plant a surveying-staff, and with the graphometer, go to A and find the angle formed by B A C.

Suppose for example, it reads 84 degrees. Repeating the operation at B for the measure of the angle C B A, suppose it to be 95 degrees. Measure the distance from A to B and let it be 80 yards.

Now here is the statement of our problem:

How to resolve a triangle of which the base is known to be 10 yards, and two of its angles. Well, we have said above that the sum of the three angles is always the same, equal to 180 degrees, having on one side 84, and on the other 95, that makes together 84 by 95, equal to 179 degrees. The difference between this number and 180 is 1 degree, therefore the angle ABC measures one degree.

We know that an angle of one degree corresponds to a distance of 57 yards. Multiply the base of our triangle by 57 yards and you obtain a distance of the church from the points A and B, 10 by 57, equal to 570 yards. Nothing is more simple than this.

The smaller the measured angle the further off the object will be. As seen in our figure, the upright lines, m o, m’ o’, m, o,, do not vary, but according to their distances from point C, they form various angles, ac, a’c’, a,c,, becoming smaller and smaller.

A graphometer is not always to be had. When approximate distances only are required, the following contrivance may be used. Trace on a cardboard of large size a semi-circumference which one divides first into 180 equal parts, then each of these is divided again in 2, 3, 4 divisions, etc., according to the size given to the circumference, which constitutes a large protractor.

To measure an angle place the cardboard upright in an horizontal position, supporting it by the center of the semi-circumference by means of a screw fixed on a stick. Then proceed as stated above.

From a pin stuck in the center mark the spot where the visual ray passes, go to A and to B, and you get approximately the desired result.

Practical Tracing of a Meridian Line.

The meridian line of a place is an imaginary line passing through this place and the center of the sun, when the latter is at the highest point of the arc of the circle, which it daily describes. At that very moment it is noonday exactly at the place in question.

As the position of the earth changes from day to day, the sun does not every day touch the meridian line at noon; sometimes it is in advance, sometimes behind.

Various instruments have been invented to indicate in a practical manner the meridian of a place. We owe the following construction to Mr. E. Brunner of the longitudinal office.

On a window-sill in a southerly position, fix in a solid, permanent manner, a small cupful of quicksilver; cover it with a lid made of varnished metal, and pierced in its center by a small round hole about a quarter of an inch in diameter. This lid must fit well, but not too tightly, so as to permit its being lowered in close proximity to the surface of the quicksilver.

When the window is open the solitary ray reflected on the mercury will be projected on the ceiling of the room. At the exact noonday the center of the mirror and the center of the reflected image are in the meridian plane. It remains only to be traced.

At the moment of its passage one marks in B, for example, a spot corresponding to the center of the reflected image; one knocks a small nail there, and with a string connect this point with another outside the window, so that the string passes through the center of the diaphragm, M. The line, B M, is the meridian plane. From A, suspend a lead-line which meets the string, B M.

All you have to do now is to join on the ceiling the points, A B, and continue them to D. A black thread may be stretched to serve as the line, and this is the meridian required.

To get the mean time one has only to note the exact passage, and deduct the corrections given in various astronomical papers.

To Measure the Height of a Mountain.

One can, without instruments, take the height of a building or a mountain, provided you are able to measure their base. A yardstick and two ordinary sticks are enough. Suppose the height of the tower, E F, is to be taken.

Some distance off plant a stick, a yard high, A B; one yard from this we plant another and longer one, C D. Measure exactly the distance, B F, and applying the eye at A, we aim at the summit of the tower, E; mark on the stick, C D, the point where the visual ray meets the stick, i.e., point G.

Then, by measuring the distance, D G, and subtracting one yard you get G I, and may be expressed in the following statement:

A H : A I :: E H : G I

In the given example let us suppose that A H = 150 yards, A I will, of course, be equal to one yard; G I =, say four fifths of a yard; the problem will be: 150 yards : 1 yard :: x : four fifths of a yard. Work the sum out, and the value of x is 120 yards.

Having taken our lease, A H, at one yard from the ground, we must add one yard to 120, making 121 yards, which is the height of the tower wanted.

To Take Up Four Knives with One.

Here is one more trick of equilibrium, which appears to be interesting enough to find a place among these experiments.

We need not give any long explanations, for our figure fully illustrates the way in which it has to be executed.

First place a knife straight before you, then two others which you place, blade upon blade, over the first. Finally, the two last ones are arranged transversely, their blades passing over those of the two knives put down in the second instance, and below the blade of the first knife.

By taking hold of the handle of the first knife, you can lift them up all at once without breaking the equilibrium.

The Tack in the Ceiling.

To nail a tack in the ceiling without hammer, using a ladder or chair to reach it, seems as impossible as pulling the moon down from the sky. Yet, with a little cleverness, it is quite an easy thing to do.

Place a tack, head downwards, on a half dollar, then place a small piece of tissue paper over it, so that the point of the tack passes through.

Then turn the sides of the paper down round the coin. Throw the whole, point upwards, violently against the ceiling, trying to keep this projectile of a new description from turning over on its course.

With a little practice the knack is soon acquired. The tack enters the ceiling, the violence of the shock tears the paper, which, carried away by the coin, falls to the ground.

Suppose you have a light object to suspend on the ceiling; you may do it in this manner without much trouble. Simply tie a thread to the tack, the object being attached to the other end.

If the projectile is well thrown the tack will go right in, and stick very firmly.

The Jumping Pea.

Take an unbroken straw, four or five inches long, not closed by knots, but forming a tube, and about one twentieth of an inch in diameter.

Divide one of its extremities to a length of about half an inch in four, five or six parts, which separate slightly, so as to form a truncated cone.

After having thus prepared the straw, take a dry pea, with a larger diameter than that of the tube, and place it in the cone. Hold the tube upwards, and blow into it at the opposite end.

The pea will be forced upward by the air column which you blow into the tube. It will remain suspended in the air as long as the interior pressure continues, then fall back into the arms of the cone.

To vary that experiment pass a long pin through the pea, the point of which is turned into the tube. When well thrown up, the pea can be maintained at a distance of two or three inches from the mouth of the straw. According to the stronger or weaker blast of breath, the pea will go up or down.

To Acquire a True Eye.

Here is a peculiar and clever recreation, easily performed, though at first sight it may appear difficult.

Put a tumbler upside down. By means of bread crumbs, fix a match vertically on the top. On the edge of the table place another match, partly raised on a piece of cork or wood.

Stoop down and aim at the vertical match on the glass, so that the one on the table is in the exact line of fire.

When you think it is aimed straight, give it a fillip on the lower end, it will shoot up and touch the one placed on the glass if the aim be good.

If you succeed, you may congratulate yourself on having good eyes—a very desirable gift if you should have to handle a gun, as a soldier or a sportsman.

The Air-Tight Stopper.

How many times has it happened to you, when wanting to cork a bottle, that the intended cork was too large to enter the neck?

What have you done? Cut the cork all round, and obtained, but imperfectly, the desired end.

Next time when the same occasion arises, turn the difficulty in this way: Instead of attacking the sides, cut four notches, bevel-shaped, into the cork as shown in the figure.

Treated in this manner your cork will fit, and close the bottle hermetically.

The Fusee Rocket.

For this you only want a simple match box. Take out a match, and holding it on to the box as shown in figure, i.e., hold the box a little slanting, between the thumb and forefinger, and place the match head downwards on the side of the emery paper, where the match ignites when rubbed against.

With medium force press on the match and with the other hand give it a fillip in the direction indicated by the arrow.

The little missile will fly into the air all ablaze, and fall down at a distance of four, five, or even six yards.

With a little practice you will succeed each time. It looks like a small rocket, especially when done in complete darkness.

Be careful to make the experiment only where there is no danger of setting anything on fire.

A Novel Table Mat.

To construct this original table mat 6 objects, always at hand when table is laid for a meal, are required; 3 knives and three tumblers of equal size and arrange the tumblers upside down, in the form of a triangle, and on each of them rest the handle of a knife. Cross the blades so that the first laid passes over the second and the second over the third, this latter passing over the first X.

The blades sustain themselves and you may place on them a dish or any other heavy object, without being afraid of a collapse.

The arrangement is sufficiently shown in the design with out requiring more detailed explanation.

Geometrical Paper Band.

Take a band of paper, say a postal wrapper; you observe that it has two lines and two surfaces (interior surface and exterior surface.) The problem is to arrange it so that it presents only one line and one surface. It may seem improbable, yet it is possible as you will see. Cut the band and gum together again the two pieces thus separated, after having turned over one of them as shown in figure as above. Arranged in this manner the paper has but one line and one surface, for it has the aspect of a screw without end.

Photographic Camera.

Here is a simple way to construct a camera for a pocket photographic apparatus.

Fig. 1.

Cut out of strong cardboard a piece of about 2 to 2 1/4 inches square. In the middle cut out a circle a little smaller than the lens with which you cover it, so that this lens holds on the edge of the hole.

Cut out also two triangles of cardboard, having one side equal to the square, and a length in proportion to the focus of the lens; say for a simple lens of 3 inch focus, and one inch diameter, a length of one and a half inches.

Fig. 2.

Paste the two triangles on the square at A and B, their base C must hold a rectangular mirror of the same dimensions as the side C of the square and the side of the triangles. On side D fix a roughened glass pane, or instead, a thin transparent sheet of paper; tissue paper for example.

Fig. 3.

Cut a black piece of cardboard as indicated in [Fig.] 3 C; the dotted lines indicate the sides to be turned down. This shade is fixed on to the camera.

Fig. 4.

Pass through the holes, S S, an iron rod or a long needle, which must pass likewise through the upper angle of the triangles, forming the sides, ([Fig. 1]). When your lens has been fixed on the round hole of the square your camera is complete.

The shade produces complete obscurity so that the operator can see in the middle of the camera the object or person he wishes to photograph.

In order to fix it on the photographic apparatus, one may fasten a wire, in the form of an elongated U, just below the mirror at E.

The Phantom Needle.

You know that when you sit at a window with a looking-glass in your hand, you can catch a beam of sunlight on the glass and throw it into the eyes of a person on the other side of the street.

What have you done in this case? You answer at once that you have bent the sunlight out of its course and turned it in another direction. If the glass were not there it would fall in a straight line on the window seat. This bending out of the straight line is called reflection.

Now for an experiment; cut a small round piece of cork, not quite half an inch thick. Run a needle into its center and place it in a tumbler two-thirds full of water, needle downwards.

Looking down on the cork you cannot see the needle. Now alter your position, and stoop down so that your eye is on level with the table on which the glass stands. Then you will perceive the needle to be on the top of the cork.

This apparent topsy-turveydom is called total reflection. The needle is reflected on the top of the water, and as the ray from your eye meets the top of the water, you see the needle, as it were, on the top of the cork.

Amphitrite.

At fairs, and in halls of mysteries a variety of optical illusions are presented. Under the name of Amphitrite, the spectacle is sometimes of a woman who seems to rise from the deep, moves about in the empty space, apparently without being sustained by anything or anybody.

She seems completely isolated in mid-air. She turns about, sometimes in a circle, moving now the legs, then the arms. Then after several graceful evolutions in all directions, she stands straight and descends rapidly, seemingly precipitated into a decorated scenery representing the ocean.

The illusion is produced in this way: Behind a well-stretched muslin curtain, M M, is painted D D, with the sky and clouds, below a canvas representing the sea. In front, in the direction of G G, is a mirror, without quicksilver back, inclined at an angle of forty-five degrees.

Below the mirror is a round table moving on a pivot, and on this the actress, who takes the part of the Amphitrite, lays down.

In executing various movements, the table in turning, reflects in the glass the image of the person on whom a vivid light is thrown. The spectators placed at S see the image on the canvas at the back, D D. When the time comes for making the lady disappear altogether, the table, which glides on rails, is drawn off the stage, and Amphitrite seems to plunge into the waters. It is by this process that the specters and ghosts at the theaters are produced.

You can perform this illusion, based on the reflection of the light at home, in reducing its construction to the simple proportions of a small theater of marionettes.

Optical Illusions.

Illusions of the eye are numberless, and afford a wide field for experiment. For example, if you ask any one wearing a silk high hat, to what height he thinks his hat would reach if placed on the ground against the wall or door. Nine times out of ten the mark of the height guessed will be half as much again, at least a third over the real height of the hat.