12 inches high. At the end A C, place the concave mirror, the focus of
whose parallel rays is eighteen inches from the reflecting surface. At I
L place a pasteboard, blacked, in which a hole is cut, sufficiently large
to see on the mirror H the object placed at B E F D. Cover the top of
the box, from A to I, close, that the mirror H may be entirely darkened.
The other part, I B, must be covered with glass, under which is placed
a gauze or oiled paper, to prevent the inside from being seen. Make an
aperture at G, near the top of the side E B, beneath which, on the inside,
place in succession, paintings of vistas, landscapes, figures, &c. so
that they may be in front of the mirror H. Let the box be placed that the
object may be strongly illuminated by the sun, or by wax-lights placed
under the inclosed part of the box A I. By this simple construction, the
objects placed at G D will be thrown into their natural perspective, and
if the subjects be properly chosen and well executed, the appearance will
be both wonderful and pleasing.
THE MAGICAL GYROSCOPE.
A little instrument has been constructed lately, exhibiting such
remarkable results in connection with rotary motion, that it has greatly
puzzled most of those who have witnessed its strange performances.
Although many of our readers may have seen the instrument, yet from the
numberless inquiries that have been made for the rationale of its peculiar
feats, and also from the fact that we have not yet heard a solution that
appears to be the true one, we are induced to furnish a brief description
and explanation of the whole.
[Illustration: _Fig. 1_]
It consists of a brass wheel, B, four or five inches in diameter, with
a thick lead rim, or circumference, so as to impart to the wheel when
revolving rapidly sufficient momentum to cause it to spin for some
minutes. The axis of this wheel terminates in pivots, set in a circular
ring at right angles to the wheel, as the figure represents. Two small
flat pieces of brass (A and C) are soldered outside to opposite sides of
this ring, and a small cavity is made on the under side of each piece,
so that the whole may rest on a pointed upright wire, placed in one of
these cavities, this wire being inserted in a heavy metallic base to give
it solidity. A small hole is made in the axis of the wheel, so that the
end of a cord may be thrust through, the cord wound around it, and rapid
motion imparted to the wheel like the spinning of a top. This constitutes
the whole of the apparatus, which is shown in Fig. 1.
Now, by placing the wheel and its ring, on the upper end of the pointed
wire, as shown in the figure, _only one side being supported_, the wheel
and ring would of course, immediately fall by the force of gravity, there
being no support at the other side, C. But if a rapid spinning motion
is given to the wheel by means of the cord already described, and it be
placed on the point at A, _it will not fall_, but will move slowly around
on the upright point, performing a steady, revolving horizontal motion,
as long as the rapid rotary motion of the wheel continues. So steady and
uniform is this horizontal movement, that it generally suggests the motion
of the planets round the sun.
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.
[Illustration: Fig. 2]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.