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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
Photographic Camera.
Here is a simple way to construct a camera for a pocket photographic
apparatus.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration]
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.
[Illustration]
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.
[Illustration]
Again, represents two triangles. Ask which is the one whose center is
the better indicated. Every one will say, “triangle A.” Well, every one
will be wrong, it is B. Take a pair of compasses and you will easily
prove it.
[Illustration]
The same occurs with the above figure. The two parallelograms, A B, are
absolutely equal, and yet A appears to be larger than B. The two lines,
A and B are both of equal length; yet B seems a third longer than A.
The sides, AB, CD, BD of the middle figure, BE, AM, EM, etc., are
equal, yet it seems to the eye that the surface, A B E M, is longer
than the square A B C D.
There is another deception the eye is liable to. On a sheet of paper
trace several circles, having the same center. Place the sheet on your
thumb and turn it horizontally, it will then seem to you as if the
rounds turned, though you watch with the utmost attention, the illusion
will be complete.
[Illustration]
In order to terminate this series, which can be varied infinitely, we
will, in our turn, ask you this question: Which is the tallest man
of the three personages appearing in the adjoining figure? Is it the
first, the last, or the middle one?
Try to find out without any instrument of course, simply by the aid
of your eyes which you suppose exact and true. It will appear to you
at first sight that the artist has made a mistake, and has made a
bad drawing. The last _seems_ the tallest, whereas the first seems
shortened.
[Illustration]
However, measure with a pair of compasses, and the illusion will at
once disappear. The draughtsman was not mistaken; the first _is_ the
tallest, and the two others go diminishing in height.
* * * * *
This terminates our experiments on optical illusions and you will now
enter upon another field of knowledge altogether.
The Insensible Coin.
Cut a piece of cardboard about six inches long, and by sticking the
extremities together with a pin, or with gum, form a circle or ring.
Balance it carefully on the neck of a wine bottle or decanter, and on
the top of the ring place a dime, exactly over the neck of the bottle.
Now the trick to be performed is to take off the ring so that, without
touching it, the coin falls into the bottle. On the inner side of the
ring give a sharp knock with the finger, or, better still, with the
thumb and forefinger, as in shooting a marble, as shown in figure. The
ring will come off, and the coin which on account of its inertia, does
not participate in the movement, will infallibly fall into the bottle.
It is absolutely necessary to strike the interior of the circle,
because in striking it from the outside one would not get any result at
all, on account of the elasticity of the cardboard.
[Illustration]
The Asses’ Bridge.
Every schoolboy knows which is the famous geometrical theorem, commonly
called the Asses’ Bridge, and which is propounded as follows:
[Illustration]
The square constructed on the hypotenuse of a right angled triangle is
equivalent to the sum of the squares constructed on the two other sides.
If we had only to propound this terrible theorem, it would be an easy
matter, but the question is to prove it by A and B, and by means of
the triangles, similar angles, equivalents, etc. Well, instead of all
this, we give here a very simple way to prove the truth; if not quite
pedagogic, it is none the less real.
Trace on a piece of cardboard or thick paper a square, and divide into
49 parts. This done, cut it out in following the big lines. Take out
on the center one division, which add to the small square, and then
construct the figure 2.
[Illustration: Fig. 2.]
The right-angled triangle A C D will be found by the sides of the
three squares, and the sum of the two small squares constructed on
the two sides of the triangle will be equivalent to the great square
constructed on the hypotenuse. Effectively:
Square No. 1 has 9 divisions.
Square No. 2 has 16 divisions.
--
Together 25
==
And the square No. 3 has also 25 divisions. Therefore the theorem is
proved.
Another Way to Prove the Preceding Theorem.
In a square A B D C, trace four similar and equal triangles; cut them
out and dispose them as shown in Fig. 1. You will have in the middle an
empty space forming a great square, which just has one of the sides of
the hypotenuse of the right-angled triangle A E B.
[Illustration]
Trace the outlines of this square and remount the triangles one against
the other, H C E, against A E B, and C D G, against B F G, you will get
the Fig. below.
[Illustration: Fig. 1.]
The successively covered and uncovered parts of the two squares have
not changed in extent. But this time the uncovered part is formed of
the two squares 2 and 3 which correspond to those constructed on the
two other sides of the triangle, A E B.
This very simple demonstration has the advantage of being applicable to
any rectangle.
Indented Angles.
Given two sheets of paper of the same size and form of a rectangle,
fold them both in four equal parts, one lengthwise and the other
sideways, as shown below.
[Illustration: Fig. 1.]
When so folded take a fourth part off each. Part A in the figures. The
question is now to cover quite exactly one of the remaining surfaces
with the other, in cutting the latter in two perfectly equal parts.
[Illustration: Fig. 2.]
To resolve this question take the surface (parts A having been
detached), with which it is intended to cover the other, fold it again
into equal parts, but this time in the opposite way to the one in
which it was folded first, as indicated in Fig. 4: cut it out then in
following the dotted line, F L, formed by the marks of the fold; this
done one will obtain two parts absolutely equal, F L.
[Illustration: Fig. 3.]
In order to cover the other surface, Fig. 3, all that is now necessary
is to lower the angles, viz.: angle A’, must be in front of angle A,
angle B’ in front of angle B, and angle C’ in front of angle C. When
the angles are lowered in this way, the two surfaces will be quite
similar, and can be covered one by the other.
[Illustration: Fig. 4.]
This experiment can be made either with one or the other sheet, in
lowering or raising the angles.
In the example shown here it is the fourth Figure which is destined to
cover the other one.
When the operation is terminated as indicated above, part M, of Fig. 4,
will be at M’ of Fig. 3, and part O at O’ of the covert figure.
A Cheap Shooting Gallery.
With a whalebone stay busk, make a bow and draw a target on a card. For
the arrows, divide lengthwise a steel nib, choosing long shaped ones in
the form of a lance and fix each part at the end of a match. You now
have complete a saloon shooting gallery, inoffensive and sufficiently
recreative at least for your smaller friends.
[Illustration]
The Coin in Equilibrium.
Here is a curious demonstration of the balancing of bodies having their
center of gravity displaced by a counterpoise.
We propose to keep a coin horizontally in equilibrium on the rim of a
tumbler, and it must rest on the glass only by its extreme edge, as
shown by the figure which gives the complete demonstration.
[Illustration]
Take a silver dollar and place it between the prongs of two forks
covering each other, then place the edge of the coin upon the glass
and draw the handles of the forks together, or distend them till the
whole are balanced. The center of gravity will then be at the point of
contact, and you may give a slight swing without the risk of breaking
the equilibrium thus obtained.
The Submerged Coin.
In order to make the previous experiment more significant, you may
present it also in the following manner: In a soup plate place a coin;
beside the latter an inverted glass, then pour water into the plate
just to cover the coin. You then inform the spectators that you will
withdraw the coin from the plate without wetting your fingers. You will
meet with a great deal of disbelief from many of your friends looking
on. Leave them in doubt as to the success of your operation.
Cut a round piece off a cork, on the top of which place some pieces
of paper and matches, push the whole underneath the glass, light the
matches and wait. As soon as the combustion is over, you will see the
water leave the plate and enter the glass, wherein it rises, leaving
the piece absolutely dry at the bottom of the plate. You can then
execute what you offered at first--take out the coin without wetting
your fingers.
[Illustration]
As a variation of the preceding experiment, obtain a flat-bottomed
tumbler or glass goblet (but the bottom must be flat), a pocket
handkerchief and a coin. These are to be seen by everybody present.
Procure a watch glass, or a round piece of glass like an eye-glass.
This is not to be shown.
Now show to the bystanders that you place the coin (say a fifty-cent
piece, for example) in the middle of the handkerchief, and, throwing
back two sides of the latter, point out again that the coin is still in
its place.
To show that there is no deception ask someone to hold the coin in the
handkerchief.
Then place underneath it a glass containing a little water and call
out, “Hey, Presto! Fly!”
The person lets go of the coin and the noise of its falling to the
bottom of the glass is plainly heard.
You take up the handkerchief, and every one is astonished at the
disappearance of the coin, which you can produce from another person’s
hat.
Really the trick is very simple. For the coin supposed to be held in
the handkerchief you must dexterously substitute the watch glass or eye
glass. The person holding it, of course, declares he has the coin fast.
When he drops the eye glass it makes the same noise against the tumbler
as would the coin, though, of course, it cannot be seen in the water.
It is a capital trick if smoothly performed.
The Smoke Rings.
When the air of a room is very calm, have you ever noticed that tobacco
smoke rises slowly and in a nearly vertical direction? Have you never
watched with interest the grayish or bluish streaks of smoke issuing
from the smoke of a cigar or pipe? And in seeing the smoke rise in such
a capricious fashion, have you ever ascertained that it is due to the
calm of the surrounding air?
One may get some amusement out of the agitation of the atmosphere.
For the materials you only require a square or round cardboard box,
in the lid of which cut a round hole of about two inches in diameter.
In the interior of the box place two sheets of blotting paper, the
one impregnated with muriatic acid, the other with ammoniac, in equal
quantities. Immediately a whitish smoke will escape through the hole
and rise straight to the ceiling. If with both hands you give a series
of simultaneous taps on the sides of the box, you will see the smoke
issue in well defined rings, which will disperse rapidly in the air,
and succeed each other as long as you continue the pressure. These
rings are the result of the concussion of the air which you occasion in
the box. The experiments can be made also with ordinary tobacco smoke,
but it will last longer in the way we have indicated.
[Illustration]
The Walking Cork.
Stick two knives in a cork, on the same level, and opposite each
other, so as to form a balance. In the bottom of the cork, at an
equal distance, insert two pins, sufficiently deep not to bend under
the weight which they will have to carry. Rest the pins on a flat
ruler, slightly inclined, and give them a slight balancing movement.
The weight of the apparatus will fall on the pin, A, on which the
whole turns the knife placed at the side, B, will knock against the
support, and will tend to bring the apparatus again into its original
position as the oscillating movement continues, pin, B, will, in its
turn, support the whole weight, and pin, A, will shift on to the
other point, A, indicated in the figure. The walking cork will thus
continue its movement till it has gone over the course assigned to it.
This recreation is interesting, for it demonstrates once more that all
bodies are attracted by the earth, and that, as soon as they are thrown
off their balance they obey the force which constantly draws them down.
[Illustration]
The Obstinate Cork.
Take a glass or metal tube, closed at one end, and cut a stopper
in cork or india-rubber to its size so that it closes the tube
hermetically, and take care that it glides in the tube without
difficulty, and pierce it with a hole. On the top of this hole adapt
a small piece of leather, rather larger than the hole, which you must
take care to wet before proceeding with the following experiment. In
order to be able to withdraw the cork when in the tube, you take the
precaution to fasten in it both ends of a piece of string, as indicated
in the figure.
[Illustration]
These various objects being prepared, will serve to demonstrate once
more the atmospheric pressure.
Lift the valve up, force the cork into the tube towards the middle, and
when there, put the valve in its place again, and pull quickly on the
string as if trying to pull the cork out. The latter will not come out,
for the reason that producing a vacuum before itself, the atmospheric
prepare will prevent it from coming out. But if instead you draw it
gently towards you, it will offer much less resistance, because the
outer air will enter through the smallest interval between the cork
and the glass, and partly destroy the exterior pressure.
Petroleum Pulverizer.
With the aid of the compressed air reservoir you are able to conduct
various soldering operations, requiring often great heat.
Let us construct the following pulverizer:
Into a bottle of the shape shown in the figure, put some petroleum, and
introduce a glass tube that does not quite reach the bottom. Close with
wax that no air can enter, and at the upper extremity of the tube let a
fitting be embedded, a section of which is shown in the engraving. This
fitting has three openings, two horizontals and one corresponding with
the tube that is plugged into the petroleum.
[Illustration]
Adjust the india-rubber tube to the reservoir, and when the pressure
is exercised on the surface of the liquid it will force the petroleum
upwards through the tube, and thence it will be blown in a fine spray,
which burns as if coming out of an ordinary burner. The particles of
oil are mixed with air, and consequently the atoms of air are heated to
a high degree. This jet develops a heat of great intensity.
This pulverizer may serve also to disinfect rooms. You have only to
replace the petroleum with an antiseptic liquid.
Electric Attraction and Repulsion.
The poles of the same sign repel, and the contrary poles attract each
other, or, in other words, the negative, or the positive electricity
attracts the electricity of a contrary sign, whereas the electricities
of the same signs repel each other.
In order to demonstrate this principle we will contrive a little
plaything which will be as interesting as amusing to see in operation.
[Illustration]
For a pivot take a needle stuck in a cork, and, as magnetic needles,
two old corset steels will do very well. If these cannot be had a clock
spring may do instead.
Magnetize these two steel rods by rubbing them with a magnet. In the
middle of one of the rods punch a small hollow so that it may freely
move on the needle in the cork without fear of falling off. You have
thus manufactured a rough compass.
Then cut out four dolls in paper, two gentlemen and two ladies, and
stick them in the extremities of the two magnetized needles. Remember
to put at each end a figure of the opposite sex.
Now, each time you present a man to the other man, which is placed on
the magnetized needle, they will repel each other; if to a lady, the
dolls are attracted.
The explanation is easy. You will have taken care to put the puppets
on contrary poles: a man on the positive pole, a lady on the negative
pole. In this way the principle enunciated above is thoroughly proved
and easily grasped.
One may easily vary this experiment by replacing the gentlemen and
ladies by personages of actual notoriety, or of the company, in placing
them in groups which have a mutual dislike to each other, such as the
schoolmaster and pupil, etc.
The Bust of the Sage.
Every person wonders how the sensational decapitation scene is produced.
To all appearance a head is thrust through the neck opening of a
guillotine, the knife descends and the head is cut off. However, in
order that none of the fair sex may be alarmed, it may be varied as
follows:
In a cabinet a mirror is set across, sloping from the top at the back
to the front. It reflects the ceiling, which is covered with the same
material as that which is seen of the floor in front of the mirror.
In the center of the glass is cut a hole which admits of the passing
through of a man’s head. He sits or stands in under the glass at his
ease. The front edge of the mirror is concealed by a few astronomical
and geographical instruments, old folio books, skulls, etc.
The head and shoulders are made up and draped like one of the seven
wise men of Greece, and he answers questions in a grave, portentous
voice.
The Witchery of the Hand.
In order to ascertain the existence of animal magnetism the following
apparatus, very simple, and not at all difficult to construct, answers
perfectly.
Stick a pin in a cork, point upwards. On that pivot place horizontally
a sheet of paper so that it remains in perfect equilibrium.
[Illustration]
If you now put your hand over the sheet of paper, a rotary movement
will manifest itself, the sheet swerving from right to left. This
movement is caused by the influence of the hand’s magnetism.
The Perspectograph.
This simple instrument, invented by Mr. Jarlot, renders the tracing
of a sketch extremely easy, besides avoiding absolutely faults of
perspective, which is, without doubt, the principal advantage of this
instrument. Thanks to it, one obtains an easy reproduction on one plane
of objects placed on different planes.
Here is a description of this very simple instrument. A wooden frame A
B C D, with a slot in the side, A B, in which a pane of glass can slide
so as to cover the whole space of the frame, _a, b, c, d_, is fixed on
a stand.
[Illustration]
The frame is maintained in a perfectly horizontal position by means of
a water level _n n’_, placed on the lower side of the frame. At E is a
small rule moving on a hinge at E, allowing the angle to be varied at
the plane A B C D, by resting it on two supports E E’.
The supports themselves move round on an axle fixed on the rule. At the
extremity E’ of this rule is fixed a copper blade curved in E’, C’, and
pierced by a small hole of about an eighth of an inch in circumference,
the edges are made thinner as represented in the diagram placed above;
the widened part is turned toward the frame.
So much for the body of the instrument, now for the accessories. In the
slot left in side, A B C D, lower a glass pane covering the space, _a,
b, c, d_, which is not, however, a necessary condition, it depends on
the size of the design you desire to take.
This pane requires a little preparation. It is done in this way: One
chooses a pane of the desired glass, as free as possible from defects.
Cover one side only with turpentine, and which you know is a natural
varnish.
See that this coating is as thin as possible, and to ensure this, go
over the surface with a very soft brush steeped in the liquid. When
you see that the latter does not run any more, leave off brushing. Let
it dry for two days if necessary; take care, meanwhile, to protect the
varnished side from dust.
Now it remains only to show the use of the instrument. Put yourself in
front of the object you wish to represent. Put the frame in a perfectly
horizontal position, slide the pane in it, and dispose the rule, E E’
(Fig. 2), in such a manner that, when looking through the little hole,
O, you are able to see the object you want to draw.
[Illustration: Fig. 2.]
Then, with a blue or other colored pencil, trace the outlines of the
object on the glass coated with turpentine, the use of the latter being
to allow the pencil marks to fix itself on the surface. One sees that
the outlines thus obtained will be those of the real object as clearly
as possible because they are traced as seen, so to speak.
But the principal object of the instrument is not so much exactness of
outline as to get the exact proportion existing between the different
sizes of the objects placed in different planes. We will try to show
this last result by means of another figure.
Suppose A B to be an object situated at a certain distance from the eye
posted at _o_, the rays from the eye, O A O B, meets the instrument at
_a_ and _b_, and the image of this object is given by the line, _a b_.
Now, suppose A’ B’ to be another object situated beyond A B; the eye
has not changed position, it cannot do so, with reference to the glass,
on account of the small rule which is fixed; the image of the object
A’ B’, will be _a’ b’_; thus, one has the true dimensions of A’ B’, in
respect to A B.
It is precisely this proportion which must exist between the sizes of
the objects placed in different planes, which constitute perspective.
The instrument, therefore, well deserves its name of Perspectograph.
It will be observed that this apparatus obviates two difficulties:
1, that of the exactness of the sketch, in copying nature as it is
presented to the eye; 2, that of perspective. Having the sketch on
glass it is easy to transfer it on paper. Lift up the rule, E E’, so as
not to be in the way, place oiled or transparent paper on the glass,
and counter-draw the sketch on it.
You can then stick this paper on a cardboard, and, if the operator is
a designer, he may reproduce in crayon a very fine drawing. For the
shading he must use his own talent, the aim of the instrument not being
to give a finished drawing, but only a sketch, vigorously exact, and in
unexceptionable perspective.
This instrument is often very convenient. When wishing to have a
true sketch, you trace it on the glass; you then transfer it to an
oil-paper, and again on drawing paper if the former is not to be
used. Besides, if one has an exact sketch on whatever paper, you may
reproduce it in freehand, if you are blessed with any idea of drawing.
If the varnished plane has to serve again, wash it with warm water,
and let it get dry; then the varnishing can be done over again.
Camphor in Water.
If you put very small pieces of camphor on the water, you will see them
turn round each other with great velocity. These movements are due to
the diminution of the superficial tension of the liquid in the vicinity
of the pieces of camphor.
In order to stop them throw a drop of oil in the water, and you will
produce a perfect calm. One may utilize the camphor for an amusing
recreation.
Construct a small paper or cardboard boat and fasten underneath on the
hind part or stern a piece of camphor. Your boat will maneuver on the
water. Persons not initiated will be much puzzled, and be long to find
out by what contrivance this small craft is propelled.
A Simple Multiplier.
Write on a card or strong paper the letters, figures, etc., which you
want to reproduce. Then all along the lines or tracing, with a needle,
prick holes in close proximity at equal distances.
Place the sheet so prepared on a pad made of several sheets of blotting
paper, smeared with blue analine ink, or a mixture of lamp-black and
oil.
Fix the corners with tacks or drawing pins, and draw your copies by
simply placing the blank sheets over the pricked one, and press them
down. The words, figures or designs will be reproduced in dotted lines
if the holes have been well pricked. In this way a good number of
copies can be drawn.
The Drawing Room Mirror.
On one of the faces of a pane of glass smear some lamp-black mixed with
oil. If you place this glass, thus prepared, vertically on an engraving
representing flowers, fruits, birds, etc., you will obtain an infinity
of forms, some of which will be very striking.
[Illustration]
If you want to reproduce these, to fix their outlines, you have only to
interpose a transparent paper, to draw along the glass pane a line in
pencil and to trace over the part of the picture which terminates at
the foot of the pane.
Fold the transparent paper along this pencil line, and to get the
whole reproduced you have only to copy over the designs just traced.
The glass, which does the duty of a mirror, doubles the forms in a
symmetrical way, and as it is moved new forms come to view.
Elementary Gas-Burner.
Fill an old round tin box, at least two inches high, with sawdust and
pieces of blotting paper. Close it as well as possible, and introduce a
small metal, or glass, tube in the lid to a depth of about one-third of
the box.
Make the joint tight with putty. Put this box on any two supports and
place the flame of a lamp or candle underneath it.
[Illustration]
Soon the overheated sawdust and blotting paper will evolve vapors of
alcohol and combustible gases. Approach a lighted match to the upper
end of the tube and you will see the gas ignite and continue to burn.
Rapid Vegetation.
A cheap sponge can be converted into a hanging bunch of greenery for
room decoration. Plunge it into hot water, press it dry, then put
in its holes or pores seeds of millet, red clover, barley, linseed,
grasses, etc., in fact any species of plants which germinate easily
and produce, as far as possible, leaves or blades of different shades.
Place the sponge thus prepared on a vase or in a saucer, or better
still, suspend it in the recess of a window, where it may get as much
sunshine as possible. Every morning, for a week, sprinkle its surface
lightly with water. Soon the seeds will germinate and grow. In a short
time they will form a ball of greenery, making a charming decoration
for a room.
[Illustration]
Miniature Volcanoes.
In a rather large porcelain or glazed earthenware basin place a small
quantity of nitrate of lead. This may be obtained for a few cents from
any painters’ supplies store. Then upon it throw some flakes of sal
ammoniac. Immediately a number of conical elevations will be formed,
which give off vapors and burst with a popping noise.
[Illustration]
Altogether the experiment represents very exactly, volcanoes in a state
of eruption. When the eruption ceases, the rough, broken state of the
remaining mats, represents as nearly as a thing on this earth of ours
can, the appearance of the moon through a powerful telescope.
Indeed the moon at one time of its history was undoubtedly in the soft
lava-like state that you will observe in the basin, during the first
stage of this elegant and instructive experiment.
[Illustration: THE END.]
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