the window, above the level of the eye, as in the engraving. Then look
obliquely, as in the direction E, _a_, _c_, and you will see the whole
surface shining like burnished silver, with a strong metallic reflection;
and any object, as a spoon, A, C, B, immersed in the water, will have its
immersed part, C B, reflected on the surface, as in a mirror, but with a
brilliancy far surpassing that which can be obtained from quicksilver, or
from the most highly-polished metals, by any means whatever.
[Illustration]
OPTICS OF A SOAP BUBBLE.
[Illustration]
If a soap-bubble be blown up, and set under a glass, so that the motion
of air may not affect it, as the water glides down the sides and the top
grows thinner, several colors will successively appear at the top, and
spread themselves from thence down the sides of the bubble, till they
vanish in the same order in which they appear. At length, a black spot
appears at the top, and spreads till the bubble bursts.[7]
THE KALEIDOSCOPE.
[Illustration]
If any object be placed between two plane mirrors, inclined towards
each other at an angle of thirty degrees, three several images will be
perceived in the circumference of a circle. On this principle is formed
the kaleidoscope, invented by Sir David Brewster, and by means of which
the reflected images viewed from a particular point exhibit symmetrical
figures, under an infinite arrangement of beautiful forms and colors.
The kaleidoscope may be bought at any toy-shop, but it is requisite that
every young person should be able to construct one for himself. He must,
therefore, procure a tube of tin or paper, of about ten inches in length,
and two and a half or three inches in diameter. One end of this should be
stopped up with tin or paper, securely fastened, in which is to be made
a hole, about the size of a small pea, for the eye to look through. Two
pieces of well-silvered looking-glass, B B, are now to be procured; they
must be not quite so long as the tube, and they should be placed in the
tube lengthwise, at an angle of 60 degrees, meeting together in a point
at A, and separating to the points C C, the polished surfaces looking
inwards. A circular piece of glass is now to be laid on the top of the
edges of the reflectors, B B; which, by their not being quite so long as
the tube, will allow room for its falling in, and it will be supported by
the edges of the tube, which may be slightly bent over, to prevent the
glass from falling out. This having been done, now proceed to make the
"cap" of the instrument. A rim of tin or pasteboard must be cut, so as
to fit over the glass end of the tube; and in this, on the outer side,
a piece of ground glass must be fastened, so that the whole may fit on
the tube like the lid of a pill-box. Then, before putting it on, obtain
some small pieces of broken glass of various colors, beads, little strips
of wire, or any other object, and place them in the cap; and by passing
it over the end, so that the broken glass, &c. has free motion, the
instrument is complete. To use it, apply the eye to the small hole, and,
on turning it, the most beautiful forms will appear, in the most wonderful
combinations.
[Illustration]
The following curious calculation has been made of the number of changes
this instrument will admit of. Supposing it to contain 20 small pieces
of glass, and that you make 10 changes in a minute, it will take an
inconceivable space of time, _i. e._ 462,880,899,576 years, and 360 days,
to go through the immense number of changes of which it is capable.
SIMPLE SOLAR MICROSCOPE.
Having made a circular hole in a window-shutter, about three inches in
diameter, place in it a glass lens of about twelve inches focal distance.
To the inside of the hole adapt a tube, having at a small distance from
the lens a slit, capable of receiving one or two very thin plates of
glass, to which the object to be viewed must be affixed by means of a
little gum water exceedingly transparent. Into this tube fit another,
furnished at its extremity with a lens of half an inch focal distance.
Place a mirror before the hole of the window-shutter on the outside, in
such a manner as to throw the light of the sun into the tube, and you will
have a solar magic lantern.
The method of employing this arrangement of lenses for microscopic
purposes is as follows: Having darkened the room, and by means of the
mirror reflected the sun's rays on the glasses in a direction parallel
to the axis, place some small object between the two moveable plates
of glass, or affix it to one of them with very transparent gum water,
and bring it exactly into the axis of the tube; if the moveable tube
be then pushed out or drawn in, till the object be a little beyond the
focus, it will be seen painted very distinctly on a card, or piece of
white paper, held at a proper distance, and will appear to be greatly
magnified. A small insect will appear as a large animal, a hair as big
as a walking-stick, and the almost invisible eels in paste or vinegar as
large as common eels.
ANAMORPHOSES.
This is a very curious optical effect, producing a distorted and grotesque
figure from a regular one. The term is derived from two Greek words,
signifying a distortion of figure, and by its means many optical puzzles
may be produced geometrically.
Take any subject, such as the portrait of a head; divide it vertically
and horizontally with parallel lines, of which the outer sides shall form
the boundary, A, B, C, D, and the whole shall be equi-distant. Then, on a
separate piece of paper, or cardboard, prepare a drawing similar to Fig. 2
by the following means:
1. Draw a horizontal line, _a b_, equal to A B, and divide it into as many
equal parts as the latter is divided.
2. Let fall a perpendicular line, _e v_, from the middle of _a b_, and
then draw _s v_ parallel to _a b_.
3. Both _e v_ and _s v_ may be any length at pleasure, but the longer the
first is, and the shorter the other, so will the anamorphoses be more and
more deformed. The proportions in our figures are sufficiently different.
4. After having drawn from the point _v_ right lines, _v_ 1, _v_ 2, _v_ 3,
_v_ 4, to the divisions of _a b_, draw the line _s b_, and through each
point where _s b_ intersects the divergent lines, draw other horizontal
lines parallel to _a b_. We now have a _trapezium_, _a b c d_, divided
into as many cells as the square in Fig. 1.
[Illustration: _Fig. 1._]
[Illustration: _Fig. 2._]
The next step is to fill up all the cells of Fig. 2 with portions of the
device, proportionate to their position in Fig. 1. For instance, in Fig.
1 the nose is in the second vertical division from the left, and in the
third and fourth horizontal divisions from the top, and that portion of
the face must accordingly be placed in a corresponding part of Fig. 2.
By these means we procure the anamorphosis seen in Fig. 2, which, when
viewed from a particular position, will lose all its distortion, and
assume an appearance resembling that in Fig. 1. This position lies
immediately over the point _v_, and at a height above it equal to the
length of the line _s v_; and the means of determining it are as follow:
Place the drawing horizontally before a window; take a slip of card, and
rest its lower edge on the line _s v_, the card being accurately vertical;
pierce a small hole in the card vertically over the point _v_, and at
a height from it equal to the length of the line _s v_, then, with the
eye placed immediately behind the card, look through the orifice at the
anamorphosis, and it will be found that as soon as the eye has become
accustomed to the novelty of the experiment the anamorphosis will lose its
distortion, and appear almost exactly like the symmetrical figure.
It would be very difficult, and would require geometrical reasoning of a
lengthened kind, to show why this particular form of construction should
lead to such results.
THE COSMORAMA.
The principle upon which the cosmorama is formed is so simple, that any
person may easily fit up one in a small summer house, &c. Nothing more is
necessary than to fix in a hole a double convex lens of about three feet
focus, A, and at rather less than this distance a picture, B, is to be
hung. To absorb all the rays of light but those necessary for seeing the
picture, a squared frame of wood blackened on the inside is placed between
the lens and the picture. The picture may be hung in a large box having a
light coming in upon it from above, or in a small closet illuminated in
the same manner. Should it be wished to show the picture by candle-light,
a lamp, _c_, may be placed on the top of the wooden frame, and if the
light of this be converged by a lens to a moderate radius, it will be more
effective.
[Illustration]
DISTORTED LANDSCAPES.
[Illustration]
Landscapes or other matters may be drawn so as to produce curious
optical illusions by the following method. Take a piece of smooth white
pasteboard, and sketch the design upon it. Prick the outlines in every
part with a fine pin or needle, then place the pricked drawing in a
perpendicular position, and put a lighted candle behind it. Place before
it another piece of pasteboard, and follow with a pencil the lines given
by the light, and you have produced a distorted landscape. Now take
away the candle and the pricked drawing, and place your eye where the
light was, and the drawing will assume the regular form. To get your
eye in the proper position, it will be advisable to cut out a piece of
card according to the preceding pattern, and raising it on its base, B,
look through the hole at A, when the object will appear in its proper
proportions.
[Illustration]
THE MAGIC COIN.
Among the numerous experiments with which science astonishes and sometimes
even strikes terror into the ignorant, there is none more calculated
to produce this effect than that of displaying to the eye in absolute
darkness the legend or inscription upon a coin. To do this, take a silver
coin (I have always used an old one), and after polishing the surface
as much as possible, make the parts of it which are raised rough by the
action of an acid, the parts not raised, or those which are to be rendered
darkest, retaining their polish. If the coin thus prepared is placed upon
a mass of red-hot iron, and removed into a dark room, the inscription upon
it will become less luminous than the rest, so that it may be distinctly
read by the spectator. The mass of red-hot iron should be concealed from
the observer's eye, both for the purpose of rendering the eye fitter for
observing the effect, and of removing all doubt that the inscription is
really read in the dark, that is, without receiving any light, direct or
reflected, from any other body. If, in place of polishing the depressed
parts, and roughening its raised parts, we make the raised parts polished,
and roughen the depressed parts, the inscription will now be less luminous
than the depressed parts.
FOOTNOTES:
[Footnote 6: The eye is to be applied to the little circular hole seen on
the upper surface.]
[Footnote 7: The thinnest substance ever observed is the aqueous film of
the soap-bubble previous to bursting; yet it is capable of reflecting the
faint image of a candle, or the sun. Hence its thickness must correspond
with what Sir Isaac Newton calls the beginning of black, which appears in
water at the thickness of the seven hundred and fifty thousandth part of
an inch.]
TRICKS IN MECHANICS.
[Illustration: "These are machinations comical."--FORD.]
There is no subject of such importance as Mechanics, as its principles
are founded upon the properties of matter and the laws of motion; and
in knowing something of these, the tyro will lay the foundation of all
substantial knowledge.
The properties of matter are the following: Solidity (or Impenetrability),
Divisibility, Mobility, Elasticity, Brittleness, Malleability, Ductility,
and Tenacity.
The laws of motion are as follow:
1. Every body continues in a state of rest or of uniform rectilineal
motion, unless affected by some extraneous force.
2. The change of motion is always proportionate to the impelling force.
3. Action and reaction are always equal and contrary.
EXPERIMENT OF THE LAW OF MOTION.
In shooting at "taw," if the marble be struck "plump," as it is called,
it moves forward exactly in the same line of direction; but if struck
sideways, it will move in an oblique direction, and its course will be in
a line situated between the direction of its former motion and that of
the force impressed. This is called the resolution of forces.
BALANCING.
The center of gravity in a body is that part about which all the other
parts equally balance each other. In balancing a stick upon the finger,
or upon the chin, it is necessary only to keep the chin or finger exactly
under the point which is called the center of gravity.
THE PRANCING HORSE.
[Illustration]
Cut out the figure of a horse, and having fixed a curved iron wire to the
under part of its body, place a small ball of lead upon it. Place the hind
legs of the horse on the table, and it will rock to and fro. If the ball
be removed, the horse would immediately tumble, because unsupported, the
center of gravity being in the front of the prop; but upon the ball being
replaced, the center of gravity immediately changes its position, and is
brought under the prop, and the horse is again in equilibrio.
TO CONSTRUCT A FIGURE, WHICH, BEING PLACED UPON A CURVED SURFACE,
AND INCLINED IN ANY POSITION, SHALL, WHEN LEFT TO ITSELF, RETURN TO
ITS FORMER POSITION.
The feet of the figure rest on a curved pivot, which is sustained by two
loaded balls below; for the weight of these balls being much greater than
that of the figure, their effect is to bring the center of gravity of the
whole beneath the point on which it rests; consequently the equilibrium
will resist any slight force to disturb it.
TO MAKE A CARRIAGE RUN IN AN INVERTED POSITION WITHOUT FALLING.
[Illustration]
It is pretty well known to most boys, that if a tumbler of water be
placed within a broad wooden hoop, the whole may be whirled round without
falling, owing to the centrifugal force. On the same principle, if a small
carriage be placed on an iron band or rail, it will ascend the curve,
become inverted, and descend again, without falling.
TO CAUSE A CYLINDER TO ROLL BY ITS OWN WEIGHT UP HILL.
Procure a coffee canister, and loading it at F with a piece of lead, which
may be fixed in with solder, the position of the center of gravity is thus
altered. If a cylinder so constructed be placed on an inclined plane, and
the loaded part above, it will roll up hill without assistance.
[Illustration]
THE BALANCED STICK.
Procure a piece of wood, about nine inches in length and about half
an inch in thickness, and thrust into its upper end the blades of two
penknives, on either side one. Place the other end upon the tip of the
fore-finger, and it will keep its place without falling.
[Illustration]
THE CHINESE MANDARIN.
Construct out of the pith of elder a little mandarin; then provide a base
for it to sit in, like a kettle-drum. Into this put some heavy substance,
such as half a leaden bullet; fasten the figure to this, and in whatever
position it may be placed, it will, when left to itself, immediately
return to its upright position.
TO MAKE A QUARTER DOLLAR TURN ON ITS EDGE ON THE POINT OF A NEEDLE.
[Illustration]
Take a bottle, with a cork in its neck, and in it, in a perpendicular
position, a middle-sized needle. Fix a quarter dollar into another
cork, by cutting a nick in it; and stick into the same cork two small
table-forks, opposite each other, with the handles inclining downwards. If
the rim of the quarter dollar be now poised on the point of the needle, it
may easily be made to spin round without falling, as the center of gravity
is below the the center of suspension.
THE SELF-BALANCED PAIL.
You lay a stick across the table, letting one third of it project over
the edge; and you undertake to hang a pail of water on it, without either
fastening the stick on the table, or letting the pail rest on any support;
and this feat the laws of gravitation will enable you literally to
accomplish.
[Illustration]
You take the pail of water, and hang it by the handle upon the projecting
end of the stick, in such a manner that the handle may rest on it in an
inclined position, with the middle of the pail within the edge of the
table. That it may be fixed in this situation, place another stick with
one of its ends resting against the side at the bottom of the pail, and
its other end against the first stick, where there should be a notch to
retain it. By these means, the pail will remain fixed in that situation,
without being able to incline to either side; nor can the stick slide
along the table, or move along its edge, without raising the center of
gravity of the pail, and the water it contains.
TO LIFT A BOTTLE WITH A STRAW.
Take a straw, and having bent the thicker end of it in a sharp angle, as
in figure subjoined, put this hooked end into the bottle, so that the bent
part may rest against its side; you may then take the other end, and lift
up the bottle by it, without breaking the straw, and this will be the
more readily accomplished as the angular part of the straw approaches
nearer to that which comes out of the bottle. It is necessary, in order
to succeed in this feat, to be particularly careful in choosing a stout
straw, which is neither broken nor bruised; if it have been previously
bent or damaged, it is unfit for the purpose of performing this trick, as
it will be too weak in the part so bent, or damaged, to support the bottle.
[Illustration]
THE DANCING PEA.
[Illustration]
If you stick through a pea, or small ball of pith, two pins[8] at right
angles, and defend the points with pieces of sealing wax, it may be kept
in equilibrio at a short distance from the end of a straight tube by means
of a current of breath from the mouth, which imparts a rotary motion to
the pea.
THE TOPER'S TRIPOD.
[Illustration]
Place three tobacco pipes in the position shown in the engraving, the
mouth of the bowls downwards, and the lower end of the stems upon the stem
just by the bowls. This tripod, if carefully put together, will support
considerably more than a pot of ale.
OBLIQUITY OF MOTION.
[Illustration]
[Illustration]
Cut a piece of pasteboard into the following shape, and describe on it a
spiral line; cut this out with a penknife, and then suspend it on a large
skewer or pin, as seen in the engraving. If the whole be now placed on a
warm stove, or over the flame of a candle or lamp, it will revolve with
considerable velocity. The card, after being cut into the spiral, may be
made to represent a snake or dragon, and when in motion will produce a
very pleasing effect.
THE BRIDGE OF KNIVES.
[Illustration]
Place three glasses, A A A, in the form of a triangle, and arrange three
knives upon them, as shown in the figure, the blade of No. 1 over that of
No. 2, and that over No. 3, which rests on No. 1. The bridge so made will
be self-supported.
SAND IN THE HOUR-GLASS.
It is a remarkable fact, that the flow of sand in the hour-glass is
perfectly equable, whatever may be the quantity in the glass; that is, the
sand runs no faster when the upper half of the glass is quite full than
when it is nearly empty. It would, however, be natural enough to conclude
that, when full of sand, it would be more swiftly urged through the
aperture, than when the glass was only a quarter full, and near the close
of the hour.
The fact of the even flow of sand may be proved by a very simple
experiment. Provide some silver sand, dry it over or before the fire, and
pass it through a tolerably fine sieve. Then take a tube, of any length or
diameter, closed at one end, in which make a small hole, say the eighth of
an inch; stop this with a peg, and fill up the tube with the sifted sand.
Hold the tube steadily, or fix it to a wall, or frame, at any height from
a table; remove the peg, and permit the sand to flow in any measure for
any given time, and note the quantity. Then, let the tube be emptied, and
only half or a quarter filled with the sand; measure again, for a like
time, and the same quantity of sand will flow: even if you press the sand
in the tube with a ruler or stick, the flow of the sand through the hole
will not be increased.
The above is explained by the fact, that when the sand is poured into
the tube, it fills it with a succession of conical heaps, and that all
the weight which the bottom of the tube sustains is only that of the
heap which _first_ falls upon it; as the succeeding heaps do not press
downwards, but only against the sides or walls of the tube.
RESISTANCE OF SAND.
From the above experiment it may be concluded, that it is extremely
difficult to thrust sand out of a tube by means of a fitting plug or
piston; and this, upon trial, is found to be the case. Fit a piston to
a tube (exactly like a boy's pop-gun,) pour some sand in, and try with
the utmost strength of the arm to push out the sand. It will be found
impossible to do this: rather than the sand should be shot out, the tube
will burst at the sides.
FOOTNOTES:
[Footnote 8: The pins are only used to hold the pea steady before it is
blown from the pipe, as the pea alone will dance quite as well.]
TRICKS IN HYDRAULICS.
The science of Hydraulics comprehends the laws which regulate non-elastic
fluids in motion, and especially water, &c.
[Illustration]
Water can only be set in motion by two causes--the pressure of the
atmosphere, or its own gravity. The principal law concerning fluids is,
that they always preserve their own level. Hence water can be distributed
over a town from any reservoir that is higher than the houses to be
supplied; and the same principle will enable us to form fountains in a
garden, or other place. Should any of our young friends wish to form
a fountain, or jet-d'-eau, they may, by bringing a pipe from T, a
water-tank, which should be at the upper part of the house, convey the
water down to the garden. Then by leading it through the earth, underneath
the path or grass plot, and turning it to a perpendicular position, the
water will spring out, and rise nearly as high as the level of that in the
tank. The part of the pipe at B should have a turnkey, so that the water
may be let on or shut off at pleasure.
THE PUMP.
The action of the common pump is as follows: When the handle A is raised,
the piston-rod B descends, and brings the piston-valve, called the
sucker, or bucket, to another valve, C, which is fixed, and opens inwards
towards the piston. When the handle is drawn down, the piston is raised,
and, as it is air-tight, a vacuum is produced between the two valves; the
air in the valve of the pump, betwixt the lower valve and the water, then
forces open the lower valve, and rushes through to fill up this vacuum;
and the air in the pump being less dense than the external atmosphere, the
water is forced a short way up the barrel. When the piston again descends
to the lower valve, the air between them is again forced out by forcing
open the upper valve; and when the piston is raised, a vacuum is again
produced, and the air below the lower valve rushes up, and the water in
consequence is again raised a little further. This operation continues
until the water rises above the lower valve; at every stroke afterwards,
the water passes through the valve of the descending piston, and is raised
by it, on its ascent, until it issues out of the spout.
[Illustration]
THE HYDRAULIC DANCER.
[Illustration]
Make a little figure of cork, in the shape of a dancing mountebank,
sailor, &c. In this figure place a small hollow cone, made of thin leaf
brass. When this figure is placed upon any jet-d'-eau, such as that of
the fountain recommended to be constructed, it will be suspended on the
top of the water, and perform a great variety of amusing motions. If a
hollow ball of very thin copper, about an inch in diameter, be placed on
a similar cone, it will remain suspended, turning round and spreading the
water all about it.
THE SYPHON.
[Illustration]
The syphon is a bent tube, having one leg shorter than the other. It acts
by the pressure of the atmosphere being removed from the surface of a
fluid, which makes it to rise above its common level at B. In order to
make a syphon act, it is necessary first to fill both legs quite full of
the fluid; and then the shorter leg must be placed in the vessel to be
emptied. Immediately upon withdrawing the finger from the longer leg, the
liquor will flow. Any young person may form a syphon by a small piece of
leaden pipe, bent into the form above.