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.

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.

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.

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).

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.

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.

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.

The vibration of the glass when emitting the notes explains this phenomenon, although the reason that the cross should remain still when you rub beneath one of its arms is too technical for explanation here.

A Light Experiment

Why do we wear white clothes in extreme heat and dark clothes in the winter? To this question every one will answer that white clothes absorb less heat than black, and that we therefore feel the rays of the sun less.

Quite true; and yet, how is it that Polar bears and other Arctic creatures exposed to such extreme cold are clothed in white?

The fact is that not only does white absorb less heat, but it serves to retain heat, and a white coat preserves the natural warmth in the animal’s body. This is exemplified by the following experiment, for which only a tumbler is required.

Choose a glass with the lower part faced, as in Fig. 12. Color these faces black and white alternately, a little India ink serving for the former and some crushed chalk and water for the latter.

With a very small knob of wax fasten a pin to each face, as shown in the figure. Having done this place a lighted candle within the glass.

The heat, striking the interior equally, is modified by the colors painted on the outside to such an extent that after some little while the wax supporting the pins of the BLACK faces is melted, whilst the pins on the white parts remain unaffected. This shows very clearly that the white prevents the escape of internal heat, as surely as it prevents the penetration of external warmth.

The Pyrometer

We all know that metals expand under heat. The amount of such expansion may be measured by a simple little apparatus called a pyrometer.

On a wooden base, B, C (Fig. 13), make two uprights, A and D, of which A must be a half inch higher than D. Bore a hole a quarter of an inch from the top of A, but not right through the wood.

A couple of pins must be bent into the shape of a Y and driven into the top of D, as in Fig. 13. With a little sealing-wax fasten a paper pointer to the eye end of a needle and lay the needle across the pins, P, P (Fig. 14). Next place an ordinary knitting-needle in the hole at A, and rest it over the small needle with the pointer. The pyrometer is now complete.

Put a lighted candle under the knitting-needle between D and A, as in the figure, taking care that the flame plays freely upon the needle. As the latter grows hot you will notice that the pointer moves slowly from left to right, being acted upon by the hot knitting-needle passing over the axle at X.

If a small paper dial be made against the pointer, the amount of the expansion can be even more clearly observed. Of course two or even more candles may be used, the result being that the needle shows more and more expansion as it becomes hotter.

The Broken Bottle

An interesting and useful experiment with a broken bottle is depicted in Fig. 15.

Fill the broken piece with oil to whatever level you desire it to be cut, and stand it upon a perfectly level table. Now plunge a red-hot poker into the oil and hold it there for a few seconds, when there will be a loud crack, and the top of the broken part will come off, even and smooth, as in Fig. 16.

It may not be generally known that a sheet of glass may be cut regularly and evenly with a pair of strong scissors.

A glance at Fig. 17 will give an idea of how this is done. The apparatus required is a large pail of cold water and a pair of strong scissors.

Plunge the glass, the scissors, and the hands, right into the water so that no part of either scissors or glass escapes immersion. You will now find that the scissors cut cleanly without the glass cracking or splintering.

The reason for this is that the water deadens the vibrations both of the scissors and the glass, thus insuring a neat and clean fracture.

Fig. 17.—A glass-cutting experiment.