G. P. (George Payn) Quackenbos.

A natural philosphy: embracing the most recent discoveries in the various branches of physics .. online

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What does Fig. 321 represent ? 911. What is the effect of a helix on a steel bar in-




356



ELECTUO-HAGNETISil.



as to be lifted up and held suspended in the air in the mid-
dle of the helix. A bar of soft iron placed in the same po'
sition is endowed with strong magnetic properties for the
rig. 322. time, but instantly loses them when re-

moved, or when the current ceases to
pass. To be magnetized, the bar must
always be placed lengthwise of the helix,
that is, at right angles to the direction
in which the current is passing.

One of the most remarkable effects of the helix is
the suspension in the air, without any visible support,
of a heavy iron bar loaded with weights. A helix
consisting of a very long wire, forming several coils
one upon another, and charged by a powerful battery,
is held in a vertical position, as shown in Fig. 322.
An iron bar brought within the helix just at its base,
will be lifted up half way into it, and held there in
the centre of the hollow cylinder, without touching
it, as long as the current continues to pass. If pulled
down a little way, it immediately springs back to its
former position. The moment the current ceases, the
bar falls. With a powerful apparatus, a weight of
eighty pounds has been thus kept suspended in the
air.

Fig. 823. A no less interesting experiment,

showing the power of the helix, may be
performed with the apparatus repre-
sented in Fig. 323. The helix, A, is in
the form of a ring. B, C, are two semi-
circular pieces of soft iron, having their
ends accurately fitted to each other.
"When B and C are brought together so
as to form a circle, with one pair of their
joined ends within the helix, they are
endowed with so strong an attraction
for each other that two men can hardly
pull them apart.

912. Electro-Magnets. An

electro-magnet consists of a bar of soft iron within a helix.





troduced within it ? On a needle ? On a bar of soft iron ? To be magnetized, how
must the bar be placed? What is one of the most remarkable effects of the helix?
Pescribe tho experiment Describe tho experiment with tho apparatus represented



ELECTRO-MAGNETS.



357



It is strongly magnetic as long
as a current passes over the wire,
but loses its power the moment
the current ceases.

The most powerful electro-magnet is
made by bending a bar of soft iron into tho
form of a horse-shoe, as shown in Fig. 324,
and winding closely round it a large quan-
tity of insulated copper wire so as to form
a helix of several layers. The ends of the
wire, Z, C, are connected with a powerful
battery. A soft iron keeper, P N, connects
the poles, having a hook beneath, to which
weights may be attached. So strongly is
this keeper attracted that an enormous
force is required to separate it. An elec-
tro-magnet prepared as above has sup-
ported over 4,000 pounds. AN ELECTRO-MAGNET.

913. Electro-magnets furnish us with the most efficient
means of magnetizing an ordinary horse-shoe bar. The
mode of using them for this purpose is shown in Fig. 325.

Fig. 325.





The electro-magnet is applied at the bend, one pole on each arm, and
drawn towards the extremities, N, S. This is done several times on both
sides, when the bar is rendered permanently magnetic. To deprive it of its
magnetic power, reverse the process, by applying the poles of the electro-
magnet to the ends N, S, and drawing them towards the bend.

914. ELECTRO-MAGNETISM, AS A MOTIVE POWER. Wo
have seen that an electro-magnet is instantly endowed with

in Fig. 323. 912. Of what does an electro-magnet consist ? How is the most power-
ful electro-magnet made ? How great a weight has been supported with such an
electro-magnet ? 913. What is the most efficient means of magnetizing a horse-shoa



358 ELECTRO-MAGNETISM.

great attractive power for iron on being connected with a
galvanic battery, and as instantly divested of it when the
connection is severed. It may thus be made to impart
motion to an iron rod, and through it to various kinds of
machinery. So strong at one time was the impression that
the enormous attractive power of the electro-magnet could
be advantageously used as a mechanical agent, that the
United States government appropriated $20,000, and Russia
$120,000, for experiments on the subject ; and various ma-
chines were contrived in which it was used as a motive
power. In none, however, thus far invented, has it been
found to approach steam in efficiency or economy.

A boat 2S feet long with a dozen persons on board has been propelled
against the current at the rate of three miles an hour by electro-magnetic
action. A locomotive engine has also been driven from ten to twelve miles
an hour. But this is the utmost that has been effected, and in both cases
the cost of keeping the galvanic battery in operation was much greater than
that of producing an equivalent quantity of steam. The difficulty appears to
be twofold. First, the attractive power of the magnet rapidly diminishes as
ihe distance from it increases. Secondly, electric currents opposite in direc-
tion to the primary one are excited in the moving machinery ; which, in-
creasing in power .with its velocity, nullify much of the effect of the magnet.
Until these difficulties are removed, electro-magnetism can not be advan-
tageously used as a mechanical agent.

915. THE ELECTKO-MAGNETIC TELEGRAPH. Although
unavailable as a motive power, electro-magnetism has been
turned to practical account in the Telegraph, one of the
crowning triumphs of human ingenuity. For this great
invention as at present perfected, which enables us, almost
with the rapidity of thought, to communicate with distant
points, over miles of intervening land 6r sea, the world is
chiefly indebted to an American Samuel F. B. Morse.

916. Morse's Telegraph. The principles on which Morse's
Telegraph operates are as follows :



bar ? Describe the process. 914. On what principle may an electro-magnet be mado
to impart motion to an iron rod ? For what were appropriations made by the United
States government and Eussia? What has been effected with machinery moved by
electro-magnetism? How does the expense compare with that of steam? What
difficulties interfere with the usefulness of electro-magnetism as a motive power ?
S15. In what has electro-magnetism been turned to practical account ? To whom i






THE ELECTRO-MAGNETIC TELEGRAPH.



359



1. An electro-magnet may be alternately endowed with
and deprived of the property of attracting iron by connect-
ing and disconnecting it with a galvanic battery.

2. The battery may be miles away from the magnet. If
wires connect the two, the electric current will still be car-
ried to the helix and produce the same effects.

3. A person stationed near the battery may complete
and break the circuit at pleasure. As he does so, one end
of a lever placed near the poles of the distant magnet will
be attracted or released. When it is attracted, the other
end of the lever, which is furnished with a point, is made
to indent a strip of paper passed in front of it by machinery,
with dots or dashes, according to the time that the opera-
tor by the battery keeps the circuit complete. If, now,
different combinations of dots and dashes are agreed upon
to represent certain letters, it is evident that a message can
be communicated from the one point to the other.

Fig. 326 represents Morse's recording apparatus.

Tig. 32G.




the world chiefly indebted for the Telegraph ? 916. State the principles on which
Morse's Tolegraph operates. Describe Morse'a recording apparatus, and its mode of



360 ELECTKO-MAGNETISM.

A B is the electro-magnet, connected with the distant battery by the wires
L, M, which are raised on poles and insulated by glass supports. C is an
armature of soft iron attached to one end of the lever D D, so as to rest about
one-eighth of an inch above the poles of the magnet. The other end of the
lever carries a point or style, I, which is raised as C is depressed. A strip
of paper, F, F, rolled on the spool E, is made to pass in front of the style,
between the two cylinders G, H, by means of wheel-work set in motion by
the weight J when the current passes. K is a spring, to pull down the end
of the lever bearing the style when the other end is released by the magnet.
A striking apparatus was formerly connected with the machinery in such a
way as to give warning to the attendant with the first motion of the lever ;
but it is now generally dispensed with, as the clicking sound produced by
the lever is found to be sufficient for the purpose.

Instead of carrying both wires over poles from the electro-magnet to the
battery, the earth is now generally made to form one-half the circuit. This
is effected by carrying down the wire from the magnet, and connecting it
with a metallic plate buried in the ground ; a similar plate must be buried
where the battery is stationed, and a wire from the latter connected with
it. If this is done, but one wire need pass over the poles to complete the
circuit.

917. The apparatus used by the operator where the
battery is stationed, to complete and break the circuit, is
called the Signal Key. It is represented in Fig. 327.

By pressing on the knob,

Fig. 32T. the screws in which the wires

are fastened are connected,
and the circuit is completed.
On removing the hand, the
knob springs up, the circuit is
broken, and the current ceases.
If the knob is kept pressed
down, the paper at the other
end is indented with a contin-
uous line ; but by tapping on
it so as to form different com-
binations of dots and dashes.

THE SIGNAL KEY.

which stand for letters, and

are understood at both ends of the line, a message is transmitted. Accord-
ing to Morse's system, the following combinations are used to represent the
different letters and figures :



operation. "What was formerly connected with the machinery ? "Why is it now dis-
pensed with? Instead of carrying both wires over poles from the electro-magnet to
the battery, what is now the more usual arrangement ? How is the earth made to
form half of the circuit? 91T. "What is the Signal Key? Describe it, and its modo




MOKSE'S TELEGRAPH.



361



LETTERS.



a


j


b

C-


k-


-

d


m


e -


n


/


o -


h


P

q-


t - -


r - - -



To prevent confusion, a small space is left after each letter, a longer one
between words, and a still longer one at the end of a sentence. The opera-
tors in telegraph offices become so familiar with this alphabet that they un-
derstand a message from the mere clicks of the lever, without looking at
the paper on which it is recorded.

918. An electric current is transmitted by a wire to a
great distance, but not with undiminished power. When,
therefore, the stations are very far apart, the electro-
magnet is charged too feebly to make the style indent the
paper. In this case, the wire from the original battery is
made to act on a very delicate armature, so as to complete
the circuit of a second battery placed near the machine.
This Relay Battery, as it is called, acts on the recording
apparatus as described above, or transmits a fresh and vig-
orous current to another relay battery. In this way lines
of any length may be formed.

As relay batteries do not interrupt the circuit, any number of them may
be placed at intervals along a line. Each may work a recording apparatus
of its own, and a given communication may thus be registered simultane-
ously at a multitude of different stations.

Eelay batteries may be dispensed with by increasing the number of plates
employed and distributing them in groups along the line. It has been com-
puted that if a telegraph wire could be carried round the earth, 1200 of
Grove's pint cups, distributed in equi-distant groups of fifties, would supply
the galvanic power for the whole distance.

of operation. How are the different letters represented? 918. "What difficulty is
there when the current is transmitted to a great distance ? How is this remedied ?
How does the Kelay Battery act? How may a given message be registered simulta-
neously at different stations ? What may bo substituted for relay batteries ? How
many cups would supply the galvanic power for a telegraph round the earth?
16



362 ELECTRO-MAGNETISM.

919. Houses and Bain' 1 s Telegraph. Morse's appara-
tus, having been first introduced and being very simple
and not likely to get out of order, is more used than any
other, both in this country and in Europe. There are other
ingenious systems, however, which are employed to some
extent. Among these are House's Printing Telegraph and
Bain's Electro-chemical Telegraph.

House's apparatus is one of the most wonderful achievements of invent-
ive art. Making use of the electro-magnet in connection with ingenious and
somewhat intricate machinery, it enables the operator, by playing on twenty-
eight keys like those of a piano (representing the twenty-six letters and two
punctuation points), to print ordinary letters on a strip of paper at the other
end of the line at the rate of about two hundred a minute. The great advan-
tages of House's system are that there is little or no liability to mistake in
transmitting a message, and that the latter, being produced in Roman cap-
itals, need not be transcribed, but may be sent just as it comes from the
machine to the person for whom it is intended.

In Bain's Electro-chemical Telegraph no magnet is used. The point of
the wire, which is stationary, constitutes the pen, and rests lightly on a me-
tallic plate, which is made to revolve by machinery. On this plate is placed
paper which has been previously moistened with some chemical preparation
decomposable by voltaic electricity. When the connection is made by the
distant operator, the current passes from the wire to the plate through the
paper, and in passing decomposes the chemical compound with which the
paper is impregnated. The result is a deep blue spot on the paper, which
renders the dot or dash visible, just as the indentation does according to
Morse's system. As even a feeble voltaic current has the power of decom-
position, there is not the same necessity for relay batteries on Bain's line as
on either of the others.

920. Submarine Telegraphs. Submarine Telegraphs are
telegraphs connecting points separated by water, .-in which
the wire is submerged. The first successful telegraph of
this kind was laid in 1851 across the English Channel, and
connected Dover with the French coast. This was fol-
lowed by several others; and in 1858, after several unsuc-
cessful attempts, a telegraph cable nearly 2,000 miles in
length w r as laid across the Atlantic Ocean, between Valen-

t)19. AVliat other telegraph systems besides Morse's are in use? What is said of
House's apparatus ? What are its great advantages ? What is the principle involved
in Bain's Electro-chemical Telegraph ? What advantage is there connected with this
eystem? 920. What are Submarine Telegraphs? Where and when was tho first
Submarine telegraph laid ? In 1S53 what great enterprise was carried through ? De-



HISTORY OF THE TELEGRAPH. 363

tia Bay, Ireland, and Trinity Bay on the coast of New-
foundland. It consisted of a group of seven copper wires
insulated and protected by a casing of gutta-percha, the
whole surrounded by strands of iron wire, and sunk to the
bottom of the ocean, at a depth nowhere exceeding 2^ miles.

Public interest was strongly excited in this great enterprise ; but it has
thus far been doomed to disappointment. After transmitting several mes-
sages, the Atlantic Telegraph, for some unexplained reason, ceased to work,
though signals have from time to time been received. There is little doubt,
however, that the work is feasible, and that we shall soon have regular tele*
graphic communication between the opposite sides of the Atlantic.

921. History of the Telegraph. The fact that factional
electricity could be conveyed by wires to a great distance
was known more than a hundred years ago. Franklin, in
1748, set fire to alcohol by means of a wire from an elec-
trical machine carried across the Schuylkill River. The
first attempt to transmit a communication by electricity,
however, was made in 1774 by Le Sage \luh sahzh~\, a
Frenchman, at Geneva,

Le Sage used twenty-four wires insulated in glass tubes buried in the
earth, each of which represented a letter of the French alphabet. The wires
were connected with an electrical machine in the order necessary to spell out
the words, and electroscopes attached to them at the other end indicated this
order by their successive divergence to an attendant stationed there.

922. Volta's discovery in 1800 furnished afar more effi-
cient agent for telegraphic communication than frictional
electricity, and was followed in a few years by a plan for an
electro-chemical telegraph, requiring thirty-five wires, to
represent the different letters and figures, and to act by
the decomposition of water.

The great discovery of electro-magnetism in 1819 called
forth many new suggestions, among others, the use of the
deflections of the needle as signals ; but none of the plans
proposed were practicable on a large scale. A more per-



Bcribo the Atlantic cable. What is said of the working of the Atlantic telegraph?
921. What fact relating to frictional electricity was known more than a hundred years
ago? "What experiment was performed by Franklin inl~4S? Who made the first
attempt to transmit a message by electricity ? Describe the plan of Le Sago. 922. By
what was the discovery of voltaic electi-icity followed ? What suggestions were called



364 ELECTRO-MAGNETISM.

manent galvanic power was needed ; and this was not sup-
plied till 1836, when Daniell brought out his constant bat-
tery. The appearance of this battery and the improved
electro-magnets prepared by Prof. Henry, was followed in
1837 by the invention of apparatus for transmitting and
recording communications, by Samuel F. B. Morse, who
had been experimenting on the subject for five years. Ap-
plication was at once made to the Congress of the United
States for aid to construct a line of sufficient length to test
the invention ; and after discouraging delays, in 1843, the
sum of $30,000 was appropriated by that body, with which
a line was established between Baltimore and Washington,
a distance of forty miles. The enterprise was crowned with
complete success ; and the first news transmitted was the
proceedings of the democratic convention of 1844, then
sitting in Baltimore, by which James K. Polk was nomi-
nated for the presidency.

So manifold were the advantages of telegraphic communication, that im-
mediately on the announcement of Morse's success companies were formed,
and wires were soon seen threading the country in all directions. The va-
rious lines now in operation in the United States and British Provinces make
a total of about 45,000 miles, on nine-tenths of which Morse's apparatus is
used, House's and Bain's being chiefly employed on the remainder. With
Morse's instruments about 9,000 letters may be transmitted in an hour. The
construction of the line costs not far from $15P a mile.

The same year in which Morse perfected his invention (1837), plans for
telegraphic communication based on the deflections of the needle were an-
nounced by Wheatstone in England, and Steinheil [stine'-7tile], a German
philosopher, to whom the discovery that the earth could be made to com-
plete the circuit seems to be due. They are therefore sometimes mentioned
as entitled to share with Morse the honor of his great invention. Their sys-
tems, however, were but modifications of what had been proposed some years
before ; though practicable, they could not compete in rapidity of operation
with Morse's, and consequently never came into general use.

923. ELECTKO-MAGNETIC CLOCKS. American ingenuity

forth by the discovery of electro-magnetism ? By whom and when was the first per-
fect apparatus for transmitting and recording communications invented ? What two
improvements prepared the way for Morse's invention ? How was Morse enabled to
test his invention ? What was the result? What was the first news transmitted?
How many miles of telegraph are noSv in operation ? On how much of this is Morse's
apparatus used? What is the cost of constructing a telegraphic line? Who arc
sometimes mentioned as sharing with Morse the honor of inventing tho telegraph ?



ELECTRO-MAGNETIC CLOCKS. 365

has applied electro-magnetism to the determining of minute
intervals of time and the regulation of clocks. The time
of astronomical observations may thus be fixed with perfect
precision to the tenth of a second.

The pendulum of a clock, for instance, is, by some mechanical contrivance,
made by its vibrations to close and break a galvanic circuit. With Morse's
apparatus, each vibration is indicated by a dot on a strip of paper passed in
front of the style. If now an observer have a signal-key connected with the
same circuit, by depressing it the instant a star passes one of the wires of
his telescope, he permanently records its transit on the same paper by a dot
intermediate between two vibration-dots, the exact time of which is known.

924. By the same agency a number of clocks may be
made to keep uniform time.

This is effected by connecting any number of distant clocks, by means of
wires, with one standard time-piece, which is itself connected with a gal-
vanic battery, so that the circuit may be closed and broken by all the pen-
dulums simultaneously. Wheels connect the pendulums with the hands of
the clocks, which are thus made to move with perfect uniformity. Some
railroad companies use an arrangement of this kind to make the clocks at
their different stations keep time together.

925. ELECTKO-MAGNETIC FIKE-ALAKM. The principle of
the telegraph has been used for raising a simultaneous alarm
of fire at a number of difierent stations connected with one
principal station by wires. By completing and breaking
the galvanic circuit, an attendant who is constantly on watch
at the principal station, and receives his information by tel-
egraphic signals from the district in which the fire is de-
tected, strikes alarm-bells at the various distant stations a
certain number of times, according to the number of the
district in question. Such an arrangement has been used
in Boston with great success.

926. THE HELIX, A MAGNET. The helix, when traversed
by a current of electricity, not only has high magnetizing
powers, as we have seen, but is also itself a magnet. If

What is said of their claims ? 923. To what has American ingenuity applied electro-
magnetism ? Show how an astronomical observation may be telegraphically record-
ed. 924. How may a number of clocks be made to keep uniform time by means of
electro-magnetism ? 925. For what has the principle of the telegraph been used ?
Show how an alarm of fire may be simultaneously raised at different stations.
826. What is the effect of an electric current traversing a helix on tho"hclix itself?



366 MAGNETO-ELECTKICIT Y.

suspended so as to allow it freedom of motion, it points
north and south, and dips like the magnetic needle. So,
like poles of two helices repel each other ; unlike poles at-
tract each other.

Even when not bent in the form of helices, two wires traversed by elec-
tric currents, if brought near each other in parallel lines and free to move,
exhibit mutual attraction or repulsion. When their currents move in the
same direction, they attract each other ; when in contrary directions, they
repel each other.

Magiaetto-electricity.

927. Not only is magnetism developed by electric cur-
rents, but electric currents are produced by magnetism.
That branch of science which treats of electric currents so
produced is called Magneto-electricity.

The phenomena of magneto-electricity, like those of electro-magnetism,
go far towards proving the intimate connection between electricity and mag-
netism, if not their actual identity.

928. Experiments. Connect the ends of wire from a helix with a galva-
nometer. Then quickly thrust into the helix one of the poles of a bar mag-
net. The needle of the galvanometer is at once deflected, showing the pas-
sage of an electric current over the wire. If the opposite pole is introduced
into the helix, a current passes in the contrary direction.

"Within a helix place a soft iron bar of such length that each end may
project a little. Over its ends bring the poles of a horse-shoe magnet, so
suspended as to have freedom of revolution. On turning the magnet rapidly,
the poles of the bar are reversed twice for each revolution, and an electric



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 35 of 42)