communicating by means of a wire with the outside of the jar, may be
swum in water under the remaining cloud; the mast being made of separate
pieces, and but slightly joined together. When the cloud is passed over
the vessel, the mast will be struck and shattered to pieces.
[Illustration]
THE SPORTSMAN.
This apparatus is capable of affording much amusement: A is a stand of
wood, B is a common Leyden jar, out of which proceed the wires H H, one
terminating in ball F, the other in the ball D, to which are attached a
number of pith birds, by silken strings; E is a shelf for the birds to
rest upon; C is the sportsman; G his gun.
To put this operation in motion, the Leyden jar is to be charged with
electricity, by affixing a chain to the bottom part of it, and connecting
it with an electrical machine in the usual manner, or by applying it to a
prime conductor, when the birds will fly off the knob to which they are
fixed, in consequence of their being repelled. If the sportsman and gun
be then turned, so that the end of his gun shall touch the knob F, an
electric spark will pass from one to the other, a report will be heard,
and the birds will fall down as if shot, in consequence of the electricity
having been taken from the Leyden jar. There should be a communication
between the sportsman and the jar, formed of tinfoil, or some metal, as
shown by the dotted line on the stand.
[Illustration]
Such are a few of many experiments which may be made by the young
experimenter, who is fond of science and has any ingenuity; but should he
possess little love of research, no ingenuity, and would like to amuse
himself with an electrifying machine of little cost, he may sit himself
down to a
BLACK TOM CAT,
and be a Katterfelto at once.
[Illustration]
EXPERIMENTS IN GALVANISM.
1. Place a thin plate of zinc upon the upper surface of the tongue, and a
half dollar or a piece of silver on the under surface. Allow the metals to
remain for a little time in contact with the tongue before they are made
to touch each other, that the taste of the metals themselves may not be
confounded with the sensation produced by their contact. When the edges of
the metals, which project beyond the tongue, are then suffered to touch,
a galvanic sensation is produced, which it is difficult accurately to
describe.
2. Place a silver teaspoon as high as possible between the gums and
the upper lip, and a piece of zinc between the gums and the under lip.
On bringing the extremities of the metals into contact, a very vivid
sensation, and an effect like a flash of light across the eyes, will be
perceived. It is singular that this light is equally vivid in the dark and
in the strongest light, and whether the eyes be shut or open.
3. Put a silver cup or mug, filled with water, upon a plate of zinc on a
table, and just touch the water with the tip of the tongue; it will be
tasteless so long as the zinc plate is not handled, for the body does not
form a voltaic circle with the metals. Moisten your hand well, take hold
of the plate of zinc, and touch the water with your tongue, when a very
peculiar sensation, and an acid taste, will be experienced.
4. Take a piece of copper of about six inches in width, and put upon it a
piece of zinc of rather smaller dimensions, inserting a piece of cloth, of
the same size as the zinc, between them; place a leech upon the piece of
zinc, and though there appear nothing to hinder it from crawling away, yet
it will not pass from the zinc to the copper, because its damp body acting
as a conductor to the fluid disturbed, as soon as it touches the copper it
receives a galvanic shock, and of course retires to its resting-place.
5. Plunge an iron knife into a solution of sulphate of copper
(blue-stone); by chemical action, only, it will become covered with
metallic copper. Immerse in the same solution a piece of platinum, taking
care not to let it touch the iron, and no deposition of copper will take
place upon it; but if the upper ends of the metals be brought into contact
with each other, a copious deposition of copper will soon settle upon the
platinum likewise.
WITH METAL PLATES IN WATER.
[Illustration]
If we take two plates of different kinds of metal, platinum or copper, and
zinc, for example, and immerse them in pure water, having wires attached
to them above, then if the wire of each is brought into contact in another
vessel of water, a galvanic circle will be formed, the water will be
slowly decomposed, its oxygen will be fixed on the zinc wire, and at the
same time a current of electricity will be transmitted through the liquid
to the platinum or copper wire, on the end of which the other element
of water, namely, the hydrogen, will make its appearance in the form of
minute gas bubbles. The electrical current passes back again into the
zinc at the points of its contact with the platinum, and thus a continued
current is kept up, and hence it is called a galvanic circle. The moment
the circuit is broken by separating the wires, the current ceases, but is
again renewed by making them touch either in or out of the water. If a
small quantity of sulphuric acid be added to the water, the phenomenon
will be more apparent. The end of the wire attached to the piece of
platinum or copper is called the positive pole of the battery, and that of
the wire attached to the zinc is the negative pole.
[Illustration]
The current of electricity here generated will be extremely feeble, but
this can be easily increased by multiplying the glasses and the number of
the pieces of metal. If we take six such glasses instead of one, partially
fill them with dilute sulphuric acid, and put a piece of zinc and copper
into each, connecting them by means of copper wire from glass to glass
through the whole series, a stronger current of electricity will be the
result. The experimenter must be careful not to let the wire and zinc
touch each other at the bottom of the tumblers, and must also remember
that the copper of glass 1 is connected with the zinc of glass 2, and so
on.
TO MAKE A MAGNET BY GALVANISM.
To effect this, make a connection between the poles of the above or any
excited battery with the two ends of a wire formed into a spiral coil,
by bending common bonnet wire closely round a cylinder, or tube, of
about an inch in diameter; into this coil introduce a needle, or piece
of steel wire, laying it lengthways down the circles of the coil. In a
few minutes after the electric fluid has passed through the spiral wire,
and consequently round the needle or wire, the latter will be found to be
strongly magnetized, and to possess all the properties of a magnet.
EFFECTS OF GALVANISM ON A MAGNET.
If a galvanic current, or any electric current, be made to pass along a
wire, under which and in a line with it a compass is placed, it will be
found that the needle will no longer point north and south, but will take
a direction nearly across the current, and point almost east and west.
CHANGE OF COLOR BY GALVANISM.
Put a teaspoonful of sulphate of soda into a cup, and dissolve it in hot
water; pour a little cabbage blue into the solution, and put a portion
into two glasses, connecting them by a piece of linen or cotton cloth
previously moistened in the same solution. On putting one of the wires
of the galvanic pole into each glass, the acid accumulates in the one,
turning the blue to a red, and the alkali in the other, rendering it
green. If the wires be now reversed, the acid accumulates eventually in
the glass where the alkali appeared, while the alkali passes to the glass
where the acid was.
THE GALVANIC SHOCK.
If the ends of the wires of a galvanic battery be placed in separate
basins of water, then, on dipping the fingers of each hand in the basin,
a smart shock will be felt, with a particular aching accompanied with
trembling. With a strong battery this effect is felt as high as the
shoulders. The shock will also be felt by simply holding the galvanic
wires, one in each hand, provided the hands be moistened with salt and
water. Several persons may receive the shock together by joining hands.
FAMILIAR GALVANIC EFFECTS.
Coat the point of your tongue with tin-foil, and its middle part with gold
or silver leaf, so that the two metals touch, when a sourish taste will be
produced. This simple effect is termed "A Galvanic Tongue."
Ale and porter drink better out of a pewter or tin pot, than from glass or
earthenware; because of the galvanic influence of the green copper as used
to give the beer a frothy head.
Galvanic experiments may be made with the legs of a frog. A live flounder
will answer nearly the same purpose. Lay the fish in a plate, upon a slip
of zinc, to which is attached a piece of wire, and put a quarter dollar
upon the flounder's back; then touch the quarter dollar with the wire, and
at each contact strong muscular contractions will be produced.
[Illustration]
EXPERIMENTS IN MAGNETISM.
1. We have said that the agency of the magnet can be imparted to hard
metallic bodies; this may be done in a very easy way. If you pass a magnet
(which may be either natural or artificial) over a sewing-needle several
times from the eye to the point, the needle will acquire the principle,
and attract iron filings in the same manner as a natural magnet would do.
But the part of the magnet which you apply to the needle must be the north
pole; and you must not pass it over the needle backward and forward, but
lift it always from the point and again begin from the eye. Suppose you
wish to impart the principle to a small bar of tempered steel, tie the
piece to be magnetized to a poker with a piece of silk, and hold the part
of the poker to which it is attached in the left hand; take hold of the
tongs, a little below the middle, with the right hand, and rub the steel
bar with them, moving the tongs from the bottom to the top, and keeping
them steadily in a vertical position all the time. About a dozen strokes
on each side will impart sufficient magnetic power to the bar to enable
the operator to lift up small pieces of iron and steel with it. The lower
end of the bar should be marked before it is fastened to the poker, so
that the poles may be readily distinguished from each other when it is
taken off; the upper end being the south pole, and the lower the north.
[Illustration]
2. Scatter some iron filings upon a piece of paper, and hold a magnet
underneath it. The instant the contact takes place, the filings will raise
themselves upright, and fall down as soon as the magnet is withdrawn. The
effect is singular, and indeed very amusing; the diminutive iron particles
rising and falling, as if by supernatural agency.
TEST OF MAGNETIC POWER.
To ascertain whether a piece of metal, or mineral, is magnetic, present it
to one of the poles of a poised magnet. If it be attracted at both poles,
you may then conclude that the substance so tested is not magnetic.
Dip a magnet into boiling water, and it will lose half of its magnetism;
but as the magnet cools, its full power will return.
TO MAKE ARTIFICIAL MAGNETS.
This may be done by stroking a piece of hard steel with a natural or
artificial magnet. Take a common sewing-needle, and pass the north pole of
a magnet from the eye to the point, pressing it gently in so doing. After
reaching the end of the needle, the magnet must not be passed back again
towards the eye, but must be lifted up and applied again to that end, the
friction being always in the same direction. After repeating this for a
few times, the needle will become magnetized, and attract iron filings, &c.
HOW TO MAGNETIZE A POKER.
Hold it in the left hand in a position slightly inclined from the
perpendicular, the lower end pointing to the north, and then strike it
smartly several times with a large iron hammer, and it will be found to
possess the powers of a magnet, although but slightly.
TO SHOW MAGNETIC REPULSION AND ATTRACTION.
[Illustration: _Fig. 1._
_Fig. 2._]
Suspend two short pieces of iron wire, N S, N S, so that they will hang
in contact in a vertical position. If the north pole of a magnet N be now
brought to a moderate distance between the wires, they will recede from
each other as in figure 1.
The ends S S being made south poles by induction from the north pole N,
will repel each other, and so will the north poles N N. This separation
of the wires will increase as the magnet approaches them, but there will
be a particular distance at which the attractive force of N overcomes the
repulsive force of the poles S S, and causes the wires to converge as in
figure 2; the north poles N N still exhibiting their mutual repulsion.
VARIATION OF THE NEEDLE.
The magnetic needle does not point exactly north and south, but the north
pole of the needle takes a direction considerably to the west of the true
north. It is constantly changing, and varies at different parts of the
earth, and at different times of the day.
DIP OF THE NEEDLE.
Another remarkable and evident manifestation of the influence of the
magnetism of the earth upon the needle is the inclination or dip of the
latter, which is a deviation from its horizontal place in a downward
direction in northern regions of its north, and in southern regions of its
south pole. The causes of the dipping of the needle are yet unexplained.
In balancing the needle on the crd, on account of this dipping, a small
weight or moveable piece of brass is placed on one end of the needle, by
the shifting of which either nearer to or further from the center, the
needle will always be balanced.
TO SUSPEND A NEEDLE IN THE AIR BY MAGNETISM.
Place a magnet on a stand to raise it a little above the table; then bring
a small sewing-needle containing a thread, within a little distance of the
magnet, keeping hold of the thread to prevent the needle from attaching
itself to the magnet. The needle in endeavoring to fly to the magnet, and
being prevented by the thread, will remain curiously suspended in the air,
like Mahommed's coffin.
MAGNETISM BY HAMMERING.
Place a bar of iron in a vertical position, and give it a series of slight
blows with a hammer or poker, when it will acquire a feeble degree of
magnetism; hence it happens, that the anvils and other tools employed in
smithies are endowed with magnetism.
It is, however, a remarkable circumstance, that if you strike a magnet
its magnetizing force will be either very much impaired, or altogether
destroyed.
Percussion and friction in the required position would seem, from this
and preceding experiments, to be the chief means of magnetizing iron and
steel. These operations, as it were, waken up the inert particles of the
metal to admit new magnetism, or to develop that which already resides in
it, originally derived from the earth.
POWER OF THE ELECTRO MAGNET.
[Illustration]
The same influence which affects the magnetic needle already described,
will also communicate magnetism to soft iron. If a bar of that metal, bent
as in the drawing, be surrounded with a common bonnet wire, or a copper
wire prevented from touching the iron by a winding of cotton or thread,
and then if a current of voltaic electricity be sent through the wire,
the bar becomes a powerful magnet, and will continue so as long as the
connection with the battery is preserved. On breaking the contact, the
magnetism disappears. This experiment may be easily made by the young
reader with a horse-shoe magnet, surrounded by several coils of wire. P is
the positive and N the negative pole.
THE MARINER'S COMPASS.
The mariner's compass is an artificial magnet fitted in a proper box,
and consists of three parts--1, the box; 2, the card or fly; and 3, the
needle. The box is suspended in a square wooden case, by means of two
concentric brass circles called gimbals, so fixed by brazen axes to the
two boxes, that the inner one, or compass-box, retains a horizontal
position in all motions of the ship. The card is a circular piece of paper
which is fastened upon the needle, and moves with it. The outer edge of
the card is divided into thirty-two points, as shown in the engraving,
called points of the compass. The needle is a slender bar of hardened
steel, having a hollow agate cup in the center, which moves upon the point
of a pivot made of brass.
[Illustration]
TO MAKE ARTIFICIAL MAGNETS WITHOUT THE AID EITHER OF NATURAL LOADSTONES OR
ARTIFICIAL MAGNETS.
[Illustration]
Take an iron poker and tongs, or two bars of iron, the larger and the
older the better, and fixing the poker upright, hold to it with the left
hand near the top P by a silk thread, a bar of soft steel about three
inches long, one fourth of an inch broad, and one twentieth thick; mark
one end, and let this end be downwards. Then grasping the tongs T with
the right hand a little below the middle, and keeping them nearly in a
vertical line, let the bar B be rubbed with the lower end L of the tongs,
from the marked end of the bar to its upper end, about ten times on each
side of it. By this means the bar B will receive as much magnetism as will
enable it to lift a small key at the marked end; and this end, the bar
being suspended by its middle or made to rest on a joint, will turn to the
north, and is called its north pole, the unmarked end being the south
pole. This is the method recommended by Mr. Caxton, in his process, which
he regarded superior to those in former use, and of which a more detailed
account will be found in his interesting volume.
THE WATCH MAGNETIZED.
Borrow a watch from the company, and inquire if it will go when laid
on the table. Then place it just over the point at which a magnet is
fixed underneath the top of the table, and the magnet will attract the
balance-wheel of the watch, and cause it to stop.
NORTH AND SOUTH POLES OF THE MAGNET.
[Illustration]
Each magnet has its poles, north and south, the north or south poles of
one magnet, repel the north and south pole of another. If a magnet, as
in the following figure, be dipped in some iron filings, they will be
immediately attracted to one end. Supposing this to be the north pole,
each of the ends of the filings, not in contact with the magnet, will
become north poles, while the ends in contact will by induction become
south poles. Both will have a tendency to repel each other, and the
filings will stand on the magnet as in the figure.
POLARITY OF THE MAGNET.
The best method of proving this is to take a magnet or a piece of steel
rendered magnetic, and to place it on a piece of cork by laying it in a
groove cut to receive it. If the cork be placed in the center of a basin
of water, and allowed to swim freely on its surface, so that it is not
attracted by the sides of the basin, it will be found to turn its north
pole to the north, and its south pole to the south, the same as the
mariner's compass. If you fix two magnets in two pieces of cork, and place
them also in a basin of water, and they are in a parallel position with
the same poles together, that is, north to north, and south to south, they
will mutually repel each other; but if the contrary poles point to one
another, as north to south, they will be attracted.
[Illustration]
MAGNETIC ACTION AND REACTION.
A magnet and a piece of iron attract each other equally, whatever
disproportion there is between their sizes. If either be balanced in a
scale, and the other be brought within a certain distance beneath it,
the very same counterpoise will be required to prevent their approach,
whichever be in the scale. If the two were hanging near each other, as
pendulums, they would approach and meet, but the little one would perform
more of the journey in proportion to its littleness.
TO PASS MAGNETISM THROUGH A BOARD.
Place a common sewing-needle on a smooth horizontal board, and move a
strong magnet underneath the board, when the needle will revolve along the
board, according to the peculiar motion given to the magnet.
THE MAGNETIC TABLE.
Under the top of a common table, place a magnet that turns on a pivot,
and fix a board under it that nothing may appear. There may also be a
drawer under the table, which you pull out, to show that there is nothing
concealed. At one end of the table there must be a pin that communicates
with a magnet, and by which it may be placed in different positions;
this pin must be so placed as not to be visible to the spectators. Strew
some steel filings, or very small nails, over that part of the table
where the magnet is. Then ask any one to lend a knife, or a key, which
will then attract part of the nails or filings. Then placing your hand,
in a careless manner, on the pin at the end of the table, you alter the
position of the magnet; and giving the key to any person, you desire
him to make the experiment, which he will then not be able to perform.
You then give the key to another person, at the same time placing the
magnet, by means of the pin, in the first position, when that person will
immediately perform the experiment.
INTERESTING PARTICULARS CONCERNING THE MAGNET.
Fire-irons which have rested in one position in a room during the summer
months are often highly magnetic.
Iron bars standing erect, such as the gratings of a prison cell, or the
iron railings before houses, are often magnetic.
The uppermost of the iron tires round a carriage wheel attracts the
north end of a magnet, and has hence south polarity, while the lower end
attracting the south end of the same, has north polarity.
CONCLUSION.
The preceding experiments in Electricity, Galvanism, and Magnetism, we
have selected for the simple yet clear expositions which they offer of the
fundamental principles of those branches of philosophy; more elaborate
experiments we have refrained from inserting, as although, perhaps, more
astonishing and impressive in their effects, the costly and cumbrous
apparatus which they require, raise them far above the means of most boys,
for whose instruction and amusement we cater.
EXAGGERATED MAGNETISM.
Our readers will, doubtless, recollect several stories, in which
the powers of the magnet are greatly exaggerated. Other accounts of
its virtues, though true in fact, yet really appear, without some
consideration, to be fictitious.
In a German collection of fairy tales, in which the ancient chivalry of
the court of the famous Charlemagne, the faithful squires who attended
on his heroic knights, the damsels in distress whom they relieved, the
dwarfs who were their friends, and the giants and magicians who "worked
their earthly woe," are the principal characters, we remember a passage to
the effect following: "The knight, who volunteered to adventure forward
from the body of cavalry that were bent on this exploit, to reconnoitre
the position of this gigantic enchanter's castle, had scarcely approached
within sight of it, when he beheld the enormous bulk of the giant himself
leaning against the outward wall. Pursuant to the instructions he had
received, the knight, forthwith, turned his gallant steed's head towards
his companions in arms, and, at a swift pace, came pricking o'er the
plain. He now heard the giant in pursuit, and struck his spurs into his
good steed's flank; but, alas! he had scarcely approached within view
of the chivalric troop, when the mighty hand of the giant magician was
stretched forth, armed only with one of his horse's shoes, which was
made of loadstone, and, by its attractive powers on his steel armor, his
grieved associates had the mortification of seeing the knight unhorsed."
THE MAGIC OF
PNEUMATICS AND AËROSTATICS.
[Illustration]
"There is a tricksey spirit in the air
That plays sad gambols."--BEN JONSON.
The branch of the physical sciences which relates to the air and its
various phenomena is called Pneumatics. By it we learn many curious
particulars. By it we find that the air has weight and pressure, color,
density, elasticity, compressibility, and some other properties with which
we shall endeavor to make the young reader acquainted by many pleasing
experiments, earnestly impressing upon him to lose no opportunity of
making physical science his study.