Place two concave mirrors at about 12 or 15 feet distance from each
other, and let the axis of each be in the same line. In the focus of
one of them place a live coal, and in the focus of the other place
some gunpowder. With a pair of double bellows, which make a continual
blast, keep constantly blowing the coal, and notwithstanding the
distance between them, the powder will presently take fire.
_The Igniting Mirrors._
The rays of a luminous body placed in the focus of concave mirror,
being reflected in parallel lines, and a second mirror being placed
diametrically opposite to the first, will set fire to a combustible
body, by collecting those rays in the focus.
_The Armed Apparition._
If a person with a drawn sword place himself before a large concave
mirror, but further from it than its focus, he will see an inverted
image of himself in the air, between him and the mirror, of a less
size than himself. If he steadily present the sword towards the centre
of the mirror, an image of the sword will come out from it, point to
point, as if to fence with him; and by his pushing the sword nearer,
the image will appear to come nearer to him, and almost to touch his
breast. If the mirror be turned 45 degrees, or one-eighth round, the
reflected image will go out perpendicularly to the direction of the
sword presented, and apparently come to another person placed in the
direction of the motion of the image, who, if he be unacquainted with
the experiment, and does not see the original sword, will be much
surprised and alarmed.
_The Phantom._
You inform a person that at a certain hour, and in a certain place, he
shall see the apparition of a deceased friend, (whose portrait you
possess.) In order to produce this phantom, there must be a door which
opens into an apartment to which there is a considerable descent.
Under that door you are to place the portrait, which must be inverted
and strongly illuminated, that it may be brightly reflected by the
mirror, which must be large and well polished. Then having introduced
the incredulous spectator at another door, and placed him in the
proper point of view, you suddenly throw open the door, when to his
great surprise he will view the apparition of his friend.
_The Distorting Mirror._
Opticians sometimes grind a glass mirror concave in one direction
only, or longitudinally; it is in fact a concave portion of a
cylinder, the breadth of which may be considered that of the mirror. A
person looking at his face in this mirror, in the direction of its
concavity, will see it curiously distorted in a very lengthened
appearance; and by turning the cylindrical mirror a quarter round, his
visage will appear distorted another way, by an apparent increase in
width only. If in a very near situation before it, you put your finger
on the right hand side of your nose, it will appear the same in the
mirror; but if in a distant situation, somewhat beyond the centre of
concavity, you again look at your face in the mirror, your finger will
appear to be removed to the other side of your nose.
_Water colder than Ice._
Put a lump of ice into an equal quantity of water, heated to 176
degrees, the result will be, that the fluid will be no hotter than
water just beginning to freeze; but if a little sea salt be added to
the water, and it be heated only to 166 or 170, a fluid will be
produced _colder than the ice was at first_.
_Exploding Salt._
If a small quantity of powdered charcoal and hyper-oxymuriate of
potash be rubbed together in a mortar, an explosion will be produced,
and the charcoal inflamed. Three parts of this salt, and one of
sulphur, rubbed together in a mortar, produce a violent detonation. If
struck with a hammer on an anvil, there is an explosion like the
report of a pistol.
When concentrated sulphuric acid is poured upon this salt, there is a
considerable explosion; it is thrown about to a great distance,
sometimes with a red flame; and there is exhaled a brown vapour,
accompanied with a strong odour.
_Dioptrical Paradox._
Construct a machine similar to that in Fig. 25. Its effect will be,
that a print, or an ornamented drawing, with any object, such as an
ace of diamonds, &c. in the centre F, will be seen as an ace of clubs
when placed in the machine, and viewed through a single plane glass
only, contained in the tube E. The glass in the tube F, which produces
this surprising change, is somewhat on the principle of the common
multiplying glass, as represented at G, which, by the number of its
inclined surfaces, and from the refractive power of the rays
proceeding from the objects placed before it shows it in a multiplied
state. The only difference is, that the sides of this glass are flat,
and diverge upwards from the base to a point in the axis of the glass
like a cone; it has six sides, and each side, from its angular
position to the eye, has the property of refracting from the border of
the print F, such a portion of it (designedly placed there) as will
make a part in the composition of the figure to be represented; for
the hexagonal and conical figure of this glass prevents any part of
the ace of diamonds being seen; consequently the ace of clubs being
previously and mechanically drawn in the circle of refraction in six
different parts of the border, at 1, 2, 3, 4, 5, 6, and artfully
disguised in the ornamental border, by blending them with it, the
glass in the tube at E will change the appearance of the ace of
diamonds, F, into the ace of clubs, G. In the same manner many other
prints undergo similar changes, according to the will of an ingenious
draughtsman who may design them. The figure of the glass is shown at
H.
[Illustration: Fig. 25.]
_To show the Spots in the Sun's Disk by its Image in the Camera
Obscura._
Put the object-glass of a ten or twelve feet telescope into the
scioptric ball, and turn it about till it be directly opposite the
sun. Then place the pasteboard mentioned in page 16, in the focus of
the lens, and you will see a clear bright image of the sun, about an
inch diameter, in which the spots on the sun's surface will be exactly
described.
As this image is too bright to be seen with pleasure by the naked eye,
you may view it through a lens whose focus is at six or eight inches
distance, which, while it prevents the light from being offensive,
will, by magnifying both the image and the spot, make them appear to
greater advantage.
_The Diagonal Opera Glass._
By the diagonal position of a plane mirror, a curious opera-glass is
constructed, by which any person may be viewed in a theatre or public
company without knowing it. It consists only in placing a concave
glass near the plane mirror, in the end of a short round tube, and a
convex glass in a hole in the side of the tube, then holding the end
of the tube with the glass to the eye, all objects next to the hole in
the side will be reflected so as to appear in a direct line forward,
or in a position at right angles to the person's situation who is
looked at. Plane glasses, instead of a convex and concave, may be
used; in this case the size of the object will not be increased, but
it will appear brighter.
_To observe an Eclipse of the Sun, without Injury to the Eye._
Take a burning-glass, or spectacle-glass, that magnifies very much;
hold it before a book or pasteboard, twice the distance of its focus,
and you will see the round body of the sun, and the manner in which
the moon passes between the glass and the sun, during the whole
eclipse.
_The Burnt Writing restored._
Cover the outside of a small memorandum book with black paper, and in
one of its inside covers make a flap, to open secretly, and observe
there must be nothing over the flap but the black paper that covers
the book.
Mix soot with black or brown soap, with which rub the side of the
black paper next the flap; then wipe it clean, that a white paper
pressed against it will not receive any mark.
Provide a black-lead pencil that will not mark without pressing hard
on the paper. Have likewise a small box, about the size of a
memorandum book, and that opens on both sides, but on one of them by a
private method. Give a person a pencil and a slip of thin paper, on
which he is to write what he thinks proper; you present him the
memorandum book at the same time, that he may not write on the bare
paper. You tell him to keep what he writes to himself, and direct him
to burn it on the iron plate laid on a chafing-dish of coals, and give
you the ashes. You then go into another room to fetch your magic box,
before described, and take with you the memorandum book.
Having previously placed a paper under the flap in the cover of the
book, when he presses hard with the pencil, to write on his paper,
every stroke, by means of the stuff rubbed on the black paper, will
appear on that under the flap. You therefore take it out, and put it
into one side of the box.
You then return to the other room, and taking a slip of black paper,
you put it into the other side of the box, strewing the ashes of the
burnt paper over it. Then shaking the box for a few moments, and at
the same time turning it dexterously over, you open the other side,
and show the person the paper you first put in, the writing on which
he will readily acknowledge to be his.
If there be a press or cupboard that communicates with the next room,
you need only put the book in the press, and your assistant will open
it, and put the paper in the box, which you presently after take out,
and perform the rest of the amusement as before.
There may likewise be a flap on the other cover of the book; and you
may rub the paper against that with red lead. In this case you give
the person the choice of writing either with a black or red pencil;
and present him the proper side of the book accordingly.
_The Opaque Box made Transparent._
Make a box three or four inches long, and two or three wide, and have
a sort of perspective-glass, the bottom of which is the same size with
the box, and slides out, that you may privately place a paper on it.
The sides of this perspective are to be of glass, covered on the
inside with fine paper.
Let a person write on a slip of paper, putting your memorandum book
under it, as in the last amusement; then give him the little box, and
let him put what he has written into it. In the mean time you put the
memorandum book into the press, where the perspective is already
placed. Your assistant then takes the paper out of the book, and puts
it at the bottom of the perspective; which you presently take out of
the press, and direct the person to put the little box that contains
the paper under it. You then look in at the top of the perspective,
and feigning to see through the top of the box, you read what is
written on the paper at the bottom of the perspective.
With this perspective box you may perform another amusement, which is,
by having in a bag twelve or more ivory counters, numbered, which you
show to the company, that they may see all the numbers are different.
You tell a person to draw any one of them, and keep it close in his
hand. You then put the bag in the press, when your assistant examines
the counters, and sees which is wanting, and puts another of the same
number at the bottom of the perspective, which you then take out, and
placing the person's hand close to it, look in at the top, and
pretending to see through his hand, you name the number on the counter
in it.
_The Transposable Pieces._
Take two guineas and two shillings, and grind part of them away, on
one side only, so that they may be but half the common thickness; and
observe, that they must be quite thin at the edge; then rivet a guinea
and a shilling together. Lay one of these double pieces, with the
shilling upwards, on the palm of your hand, at the bottom of your
three first fingers, and lay the other piece with the guinea upwards
in the like manner, in the other hand. Let the company take notice in
which hand is the guinea, and in which is the shilling. Then as you
shut your hands, you naturally turn the pieces over, and when you open
them again, the shilling and the guinea will appear to have changed
their places.
_The Penetrative Guinea._
Provide a large tin box, of the size of a large snuff-box, and in this
place eight other boxes, which will go easily into each other, and let
the least of them be of a size to hold a guinea. Each of these boxes
should shut with a hinge, and to the least of them there must be a
small lock, that is fastened with a spring, but cannot be opened
without a key;--observe, that all these boxes must shut so freely,
that they may be all closed at once. Place these boxes in each other,
with their tops open, in the drawer of the table on which you make
your experiments; or, if you please, in your pocket, in such a manner
that they cannot be displaced.
Then ask a person to lend you a new guinea, and desire him to mark it,
that it may not be changed. You take this piece in one hand, and in
the other you have another of the same appearance, and putting your
hand into the drawer, you slip the piece that is marked into the least
box, and shutting them all at once, you take them out; then showing
the piece you have in your hand, and which the company suppose to be
the same that was marked, you pretend to make it pass through the box,
and dexterously convey it away.
You then present the box, for the spectators do not yet know there are
more than one, to any person in company, who, when he opens it, finds
another, and another, till he comes to the last, but that he cannot
open without the key, which you then give him, and retiring to a
distant part of the room, you tell him to take out the guinea himself,
and see if it be that which he marked.
This amusement may be made more surprising, by putting the key into
the snuff-box of one of the company, which you may do by asking him
for a pinch of snuff, and at the same time conceal the key, which must
be very small, among the snuff; and when the person, who is to open
the box, asks for the key, you tell him that one of the company has it
in his snuff-box. This part of the amusement may likewise be performed
by means of a confederate.
_To make Pictures of Birds with their Natural Feathers._
First take thin board or panel, of deal or wainscot, well seasoned,
that it may not shrink; then paste white paper smoothly on it, and
let it dry; if the colour of the wood show through, paste a second
paper over it. When the paper is dry, get ready any bird that you
would represent, and draw the outline as exact as you can on the
papered panel. You then paint the ground-work, stump of a tree, the
bill and legs, their proper colour, with water-colours, leaving the
body to be covered with its own natural feathers. In the space you
have left for the body, you lay on very thick gum-water, letting each
coat dry before you lay on another, and so continuing until the gum is
as thick as a shilling. Then take the feathers off the bird; and, as
you proceed, draw a camels'-hair pencil, dipped in gum-water, over the
coat of gum that you have laid on the paper, that it may more readily
adhere. As you strip the bird, you must fix the feathers in their
proper places on the board, and you shave the shafts or stems of the
larger feathers, that they may lie flat. The most ready way to perform
the operation, is to provide yourself with a pair of steel pliars to
take up and lay on the feathers with. You should prepare some small
leaden weights to lay on the feathers, that they may more readily
adhere to, and lie flat on, the gum. The part where the eye is must be
supplied by a small piece of paper, coloured and shaped like one; or
you may, probably, be able to get a glass bead that will answer the
purpose better. In order that the feathers may lie smooth and regular,
when the whole is perfectly dry, lay a book, or a flat board, with a
weight on it.
_The Art of Bronzing._
Bronzing is that process by which figures of plaster-of-paris, wood,
&c. are made to have the appearance of copper or brass. The method is
as follows:
Dissolve copper filings in aqua fortis. When the copper has
impregnated the acid, pour off the solution, and put into it some
pieces of iron, or iron filings. The effect of this will be to sink
the powder to the bottom of the acid. Pour off the liquor, and wash
the powder in successive quantities of fresh water. When the powder is
dry, it is to be rubbed on the figure with a soft cloth, or piece of
leather; but observe, that previously to the application of the bronze
powder, a dark blackish sort of green is first to be laid on the
figure: and if you wish the powder to adhere stronger, mix it with
gum-water, lay it on like paint, with a camels'-hair brush, or
previously trace the parts to be bronzed with gold size, and when
nearly dry, rub the powder over it.
_Method of taking the Impression of Butterflies on Paper._
Clip the wings off the butterfly, lay them on clean, in the form of a
butterfly when flying. Spread some thick clean gum-water on another
piece of paper, press it on the wings, and it will take them up; lay a
piece of white paper over it, and rub it gently with your finger, or
the smooth handle of a knife. The bodies are to be drawn in the space
which you leave between the wings.
_To soften Horn._
To one pound of wood-ashes, add two pounds of quick lime; put them
into a quart of water. Let the whole boil till reduced to one-third.
Then dip a feather in, and if, on drawing it out, the plume should
come off, it is a proof that it is boiled enough; if not, let it boil
a little longer. When it is settled, filter it off, and in the liquor
thus strained put in shavings of horn. Let them soak for three days;
and, first anointing your hands with oil, work the horn into a mass,
and print or mould it into any shape you please.
_To make Moulds of Horn._
If you wish to take the impression of any coin, medal, &c., previously
anoint it with oil; then lay the horn shavings over it in its softened
state. When dry, the impression will be sunk into the horn; and this
will serve as a mould to re-produce, either by plaster-of-paris, putty
and glue, or isinglass and ground egg-shells, the exact resemblance of
the coin or medal.
_To cast Figures in Imitation of Ivory._
Make isinglass and strong brandy into a paste, with powder of
egg-shells, very finely ground. You may give it what colour you
please; but cast it warm into your mould, which you previously oil
over. Leave the figure in the mould till dry, and you will find, on
taking it out, that it bears a very strong resemblance to ivory.
_To extract the Silver out of a Ring that is thick gilded, so that the
Gold may remain entire._
Take a silver ring that is thick gilded. Make a little hole through
the gold into the silver; then put the ring into aqua fortis, in a
warm place: it will dissolve the silver, and the gold will remain
whole.
_To soften Iron or Steel._
Either of the following simple methods will make iron or steel as soft
as lead:
1. Anoint it all over with tallow; temper it in a gentle charcoal
fire, and let it cool of itself.
2. Take a little clay, cover your iron with it, temper it in a
charcoal fire.
3. When the iron or steel is red-hot, strew hellebore on it.
4. Quench the iron or steel in the juice or water of common beans.
_To take a Plaster-of-Paris Cast from a Person's Face._
The person must lie on his back, and his hair be tied behind. Into
each nostril put a conical piece of paper, open at each end to allow
of breathing. The face is to be lightly oiled over, and the plaster
being properly prepared is to be poured over the face, (taking care
that the eyes are shut,) till it is a quarter of an inch thick. In a
few minutes the plaster may be removed. In this a mould is to be
formed, from which a second cast is to be taken, that will furnish
casts exactly like the original.
_Curious Experiment with a Glass of Water._
Saturate a certain quantity of water in a moderate heat, with three
ounces of sugar; and when it will no longer receive that, there is
still room in it for two ounces of salt of tartar, and after that for
an ounce and a drachm of green vitriol, nearly six drachms of nitre,
the same of sal-ammoniac, two drachms and a scruple of alum, and a
drachm and half of borax.
_To make Artificial Coruscations._
There is a method of producing artificial coruscations, or sparkling
fiery meteors, which will be visible, not only in the dark but at
noon-day, and that from two liquors actually cold. The method is
this:--Fifteen grains of solid phosphorus are to be melted in about a
drachm of water: when this is cold, pour upon it two ounces of oil of
vitriol; let these be shaken together in a large phial, and they will
at first heat, and afterwards will throw up fiery balls in great
number, which will adhere like so many stars to the sides of the
glass, and continue burning a considerable time; after this, if a
small quantity of oil of turpentine be poured in without shaking the
phial, the mixture will of itself take fire, and burn very furiously.
The vessels should be large and open at the top.
_Another Method._
Artificial coruscations may also be produced by means of oil of
vitriol and iron, in the following manner:--Take a glass vessel
capable of holding three quarts: put into this three ounces of oil of
vitriol, and twelve ounces of water, then warming the mixture a
little, throw in at several times two ounces, or more, of clear iron
filings: upon this, an ebullition and white vapours will arise; then
present a lighted candle to the mouth of the vessel, and the vapour
will take fire, and afford a bright fulmination or flash; like
lightning. Applying the candle in this manner several times, the
effect will always be the same; and sometimes the fire will fill the
whole body of the glass, and even circulate to the bottom of the
liquor; at others, it will only reach a little down its neck. The
great caution to be used in making this experiment, is the making the
vapour of a proper heat; for if made too cold few vapours will arise;
and, if made too hot, they will arise too fast, and will only take
fire in the neck of the glass, without any remarkable coruscation.
_To produce Fire from Cane._
The Chinese rattans, which are used, when split, for making cane
chairs, will, when dry, if struck against each other, give fire; and
are used accordingly in some places, in lieu of flint and steel.
_To make an Eolian Harp._
This instrument may be made by almost any carpenter: it consists of a
long narrow box of very thin deal, about five or six inches deep, with
a circle in the middle of the upper side, of an inch and a half in
diameter, in which are to be drilled small holes. On this side, seven,
ten, or more strings, of very fine gut, are stretched over bridges at
each end, like the bridges of a fiddle, and screwed up or relaxed with
screw pins. The strings must be all tuned to one and the same note,
and the instrument be placed in some current of air, where the wind
can pass over its strings with freedom. A window, of which the width
is exactly equal to the length of the harp, with the sash just raised
to give the air admission, is a proper situation. When the air blows
upon these strings, with different degrees of force, it will excite
different tones of sounds; sometimes the blast brings out all the
tones in full concert, and sometimes it sinks them to the softest
murmurs.
_To show the Pressure of the Atmosphere._
Invert a tall glass or jar in a dish of water, and place a lighted
taper under it: as the taper consumes the air in the jar its pressure
becomes less on the water immediately under the jar; while the
pressure of the atmosphere on the water _without_ the circle of the
jar remaining the same, part of the water in the dish will be forced
up into the jar, to supply the place of the air which the taper has
consumed. Nothing but the pressure of the atmosphere could thus cause
part of the water to rise within the jar, above its own level.
_Subaqueous Exhalation._
Pour a little clear water into a small glass tumbler, and put one or
two small pieces of phosphoret of lime into it. In a short time,
flashes of fire will dart from the surface of the water, and terminate
in ringlets of smoke, which will ascend in regular succession.
_Remarkable Properties in certain Plants._