Richard Green Parker.

A school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of online

. (page 27 of 38)
Online LibraryRichard Green ParkerA school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of → online text (page 27 of 38)
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tion his vessel is proceeding j and, although the needle varies a
little from a correcjjrpolarity, yet this variation is neither so
great, nor ro irregular as seriously to impair its use as a guide
to the vessel in its course over the pathless deep.


1131. The invention of the mariner's ompass is usual iv
ascribed to Flavio de Melfi, or Flavio Gioia, a Neapolitan, about
the year 1302. Some authorities, however, assert that it was
brought from China by Marco Paolo, a Venetian, in 1260. The
invention is also claimed both by the French and English.

^ 1132. The value of this discovery may be esti-

*as the mar- mated from the consideration that, before the use
.ncr's com- of the compass, mariners seldom trusted themselves
out of sight of land ; they were unable to make
long or distant voyages, as they had no means to find their way
back. This discovery enabled them to find a way where all is
trackless ; to conduct their vessels through the mighty ocean,
out of the sight of land ; and to prosecute those discoveries, and
perform those gallant deeds, which have immortalized the names
of Cook, of La Perouse, Vancouver, Sir Francis Drake, Nelson,
Parry, Franklin and others.

Which pole of 1133. Xhe north pole of a magnet is more
"ke^nore * powerful in the northern hemisphere, or north
powerful ? of the equator, and the south pole in the south-
ern parts of the world.

1134. When a piece of iron is brought sufficiently near to a
magnet, it becomes itself a magnet ; and bars of iron that have
ptood long in a perpendicular situation are generally found te
be magnetic.

How are arti- 1135> Artificial magnets are made by ap-
fieial magnets plying one or more powerful magnets to
pieces of steel. The end which is touched
by the north pole becomes the south pole of the new mag-
net, and that touched by the south pole becomes the north
pole. The magnet which is employed in magnetizing a
steel bar loses none of its power by being thus employed ;
and as the effect is increased when two or more magnets
are used, with one magnet a number of bars may be mag-
netized, and then combined together; by which means


fcheir power may be indefinitely increased. Such an ap-
paratus is called a compound magnet.

1136. There are several methods of making artificial magnets.
One f the most simple and effectual consists in passing a strong
horse-shoe magnet over bars of steel.

In making bar (or straight) magnets, the bars must be laid
lengthwise, on a flat table, with the marked end of one bar
against the unmarked end of the next ; and in making horse-
shoe magnets, the pieces of steel, previously bent into their
proper form, must be laid with their ends in contact, so as to
form a figure like two capital U's, with their tops joined together,
thus, c3^ ; observing that the marked ends come opposite to
those which are not marked ; and then, in either case, a strong
horse-shoe magnet is to be passed, with moderate pressure, over
the bars, taking care to let the marked end of this magnet pre-
cede and its unmarked end follow it, and to move it constantly
over the steel bars, so as to enter or commence the process at a
mark, and then to proceed to an unmarked end, and enter the
next bar at its marked end, and so proceed.

After having thus passed over the bars ten or a dozen times
jn each side, and in the same direction as to the marks, they
will be converted into tolerably strong and permanent magnets.
But if, after having continued the process for some time, the
exciting magnet be moved over the bars in a contrary direc-
tion, or if its south pole should be permitted to precede aftei
the north pole has been first used, the previously-excited mag-
netism will disappear, and the bars will be found in their original

This mode of making artificial magnets is likely. to be wholly
superseded by the new mode by electrical aid vthich will be
noticed in connexion with Electro-magnetism.

How is a com- 1137 - A compound magnet may be made by
pound magnet taking several horse-shoe magnets of equal size,
constructed? ^ after liayillg magnet i zed them, uniting them

together by means of screws.


1138. A magnetic needle is made by fastening tho steel on a
piece of ooard, and drawing magnets over it frjm the oentre

1139. A horse-shoe magnet should le kepi
How should a 7 r ,, , r

horw-ihoe armed, by a small bar ol iron or steel, connect-

magnet be kept ? ing the two poles. The bar is called " the

Interesting experiments may be made by a magnet, even of no
great power, with steel or iron tilings, email needles, pieces of fer-
ruginous substances, and black sand which contains iron. Such
substances may be made to assume a variety of amusing forms and
positions by moving the magnet under the card, paper or t:ble, on
which they are placed. Toys, representing fishes, frogs, aquatic
birds, &c., which are made to appear to bite at a hook, birds floating
on the water, &c., are constructed on magnetic principles, and sold
in the shops.

What is Eke- 1140. Electro-magnetism relates to magnet-
tro'-nagnetism? j sm w hi c h j s induced by the agency of electricity.

1141. The passage of the two kinds of electricity (namely, the
positive and the negative) through their circuit is called the elec-
tric currents ; and the science of Electro-magnet' sin explains the
phenomena attending those currents. It has already been stated
that from the connecting wires of the galvanic circle, or battery,
there is a constant current of electricity passing from the zinc to
the copper, and from the copper to the zinc plates. In the single
circle these currents will be negative from the zinc, and positive
from the copper ; but in the compound circles, or the battery, the
current of positive electricity will flow from the zinc to the copper,
and the current of negative electricity from the copper to the zinc.
From the effect produced by electricity on the magnetic needle, it
had been conjectured, by a number of eminent philosophers, that
magnetism, or magnetic attraction, is in some manner caused b^
electricity. In the year 1819, Professor (Ersted, of Copenhagen,
made the grand discovery of the power of the electric current to
induce magnetism ; thus proving the connexion between magnetism
and electricity. In a short time after the discovery of Professor
(Ersted, Mr. Faraday discovered that an electrical spark could be
taken from a magnet ; and thus the relation between magnetism
and electricity was fully proved. In a paper'published a few years
ago, this distinguished philosopher has very ably maintained ihe
identity of common electricity, voltaic electricity, magnetic electric-
ity (or electro-magnetism), thermoelectricity, and animal electric-
ity. The phenomena exhibited in all these five kinds of electricity
(Jifler merely in degree, and the state of intensity in t'^c action cf tlu;

tti.&UTKO -MAC NkTIbM. 30;)

fluid. Thi discovery of Professor Oersted has been followed uut by
Ampere, who, by his mathematical and experimental researches, has
presented a theory of the science less obnoxious to objections than
that proposed by the professor. The discovery of CErstcd was
limited to the action of the electric current on needles previously
magnetized ; it was afterwards ascertained by Sir Humphrey Davy
and M. Arago that magnetism maybe developed in steel not pre-
viously possessing it, if the steel be placed in the electric current.
Both of these philosophers, independently of each other, ascertained
that the uniting wire, becoming a magnet, attracts iron filings and
collects sufficient to acquire the diameter of a common quill ; but
the moment the connexion is broken, all the filings drop off, and the
attraction diminishes with the decaying energy of the pile. Filings
af brass or copper, or wood-shavings, are not attracted at all.

1142. All the effects of electricity and galvanism that have
hitherto been described have been produced on bodies inter-
posed between the extremities of conductors, proceeding from
the positive and negative poles. It was not known, until the
discoveries of Professor (Ersted were made, that any effect
could be produced when the electric circuit is uninterrupted

What is the It will presently be seen that this constitutes the
difference be- g rea t distinction between electricity and electro-
\ricity and magnetism, namely, that one describes the effect
electro-mag- of electricity when interrupted in its course, and
that the other more especially explains the effect of
an uninterrupted current of electricity.

What are Jie 1143. The principal facts in connexion with the

prtnctpa science of electro-magnetism are,
i a c ts of elcc-

iro-magnet- (1.) That the electrical current, passing uninter.

tsm ? ruptedly through a wire connecting the two ends

of a galvanic battery, produces an effect upon the magnetic

(2.) That electricity will induce magnetism.

(3.) That a magnet, or bundle of magnets, will induce elec-

(4.) That the combined action of electricity and magnetism, as
described in this science, produces a rotatory motion of certain
kinds of bodies, in a direction pointed out by certain laws.

(5.) That the periodical variation of the magnetic needle


from the true meridian, or, in other words, the variation of thf
compass, is caused by the influence of the electric currents.

(6.) That the magnetic influence is not confined to iron, steel
&c., but that most metals, and many other substances, may be
converted into temporary magnets by electrical action.

(7.) That the magnetic attraction of iron, steel, &c., may b
prodigiously increased by electrical agency.

(8.) That the direction of the electric current may, in ah
cases, be ascertained.

(9.) That magnetism is produced whenever concentrated elec-
tricity is passed through space.

(10.) That whila in common electrical and magnetic attrac-
tions and repulsions those of the same name are mutually
repulsive, and those of different names attract each other, in
the attractions and repulsions of electric, currents it is precisely
the reverse, the repulsion taking place only when the wires are
so situated that the currents are in opposite direction.

The consideration of the subject of electricity induced by
magnetism properly belongs to the subject of Magneto-elec-
tricity, in which connexion it will be particularly noticed.

How is the 1144. The direction of the electric current is

^rrenTo/ ascertained by means of the magnetic needle. If
electricity a sheet of paper be placed over a horse-shoe mag-
ascertained? net> an( j fi ne 1,1^ sau( l, or steel filings, be dropped
loosely on the paper, the particles will be disposed to arrange
themselves in a regular order, and in the direction of curve lines.
This is, undoubtedly, the eSect of some influence, whether that
ot electricity, or of magnetism alone, is not material at present
to decide.

How will a 1145 A magnet freely suspended tench

^magnTplace to assume a position at right angles to the

itself in relation direction of a current of electricity passing

to the electrical

Current? near jt '

11UJ. If a wire, which connects the extremities of a voltaie

"* LSM. 311

Buttery, be brought over and parallel with a magnetic neecTie ut
rest, or with its poles properly directed north and south, that
end of the needle next to the negative pole of the battery wi.'l
move towards the west, whether the wire be on one side of the
needle or the other, provided only that it be parallel with it.

1147. Again, if the connecting wire be lowered on either side
of the needle, so as to be in the horizontal plane in which the
needle should move, it will not move in that plane, but will have
a tendency to revolve in a vertical direction; in which, however,
it will be prevented from moving, in consequence of tjie attrac
tion of the earth, and the manner in which it is suspended
When the wire is to the east of the needle, the pole nearest to
the negative extremity of the battery will be elevated ; and
when it is on the west side, that pole will be depressed.

1148. If the connecting wire be placed below the plane in
which the needle moves, and parallel with it, the pole of the
needle next to the negative end of the wire will move towaida
the east, and the attractions and repulsions will be the reverse
of those observed in the former case.

How does the 1149. The action of the conducting-wire in
ekctrt-magnetic these cases exhibits a remarkable peculiarity.
current act? ^11 other known forceL exerted between two
points act in the direction of a straight line connecting these
points, and such is the case with electric and magnetic actions,
separately considered; but the electric current exerts its mag-
netic influence laterally, at right angles to its own course. Nor
does the magnetic pole move either directly towards or directly
from the conducting-wire, but tends to revolve around it without
changing its distance. Hence the force must be considered as
acting in the direction of a tangent to the circle in which the
magnetic pole would move.

What effect has H5Q. The two sides of an unmagnetized

a voltaic bat- . ,. -i i i ^i '

fry on unrru.g- stee ^ needle will become endued with the
r-m/ v/.i nor th and south polaiity, if tlie needle be


placed parallel with the connecting wire of a voltaic battery,
and nearly or quite in contact with it. But, if the needle
be placed at right angles with the connecting wire, it will
become permanently magnetic ; one of its extremities point-
ing to the north pole and the other to the south, when it is
finely suspended arid suffered to vibrate undisturbed.
To what may 1151. Magnetism maybe communicated

Communicated to n ' on all( ^ stee ^ by means of electricity

by the voltaic, from an electrical machine ; but the effect

battery, and . , . . .

uhat is the pro- can be more conveniently produced by means

cess called ? O f the voltaic battery. This phenomenon is

called electro-magnetic induction.

What is a 1152. A Helix is a spiral line, or a line wound

Helix ? into the shape of a cork-screw.

What use is H53. If a helix be formed of wire, and a

made of a helix , , , , , . , . , . . .

in conne.rhm " ar * stee ^ " e enclosed within the helix, on
irith the battery ? applying the conducting- wires of the battery
to the extremities of the helix, the steel bar will immediately
become magnetic. The electricity from a common electrical
machine, when passed through the helix, will produce the
same effect.

The wire which forms the helix should

And what must

first be done be coated with some non-conducting substance,
uitfi the wire of Slic h as silk wound around it : as it may then
the helix * in M n- - i

be formed into close coils, without suffering trio

electric fluids to pass from surface to surface, which would im-
pair its effect.

1155. If such a helix be so placed that it may move freely
as when made to float on a basin of water, it will be attracted
and repelled by the opposite poles of a common magnet.

1156. If a magnetic needle be surrounded by coiled wire.
covered with silk, a very minute portion of electricity through

ELECT K< >- M A (T fcTISM . 3 1 it

the wire will cause the needle to deviate from it.s proper

Wh tisar Elec H&7. A needle thus prepared is called an
ro-mag-nf.tic Electro-magnetic Multiplier. It is, ia fact, a
Muliipier very delicate electroscope, or rather galvanom-

eter, capable of pointing out the direction of the electric cur
rent in all cases.

1158. Among the most remarkable of the
What is meant A , .., ,, . ,

)>/ the Electro- ^ acts connected with the science of electro-

magnetic Rota- magnetism is what is called the Electro-
magnetic Rotation. Any wire through
which a current of electricity is passing has a tendency to
revolve around a magnetic pole in a plane perpendicular to
the current, and that without reference to the axis of the
magnet the pole of which is used. In like manner a mag
netic pole has a tendency to revolve around such a wire.

1159. Suppose the wire perpendicular, its upper end posi-
tive, or attached to the positive pole of the voltaic battery, and
its lower end negative ; and let the centre of a watch-dial rep-
resent the magnetic pole : if it be a north pole, the wire will
rotate round it in the direction that the hands move ; if it be a
south pole, the motion will be in the opposite direction. From
these two, the motions which would take place if the wire were
inverted, or the pole changed, or made to move, may be readily
ascertained, since the relation now pointed out remains constant.

1160. Fig. 166 represents the ingenious ap-
^XVM i Fig. p ara t us> invented by Mr. Faraday, to illustrate
the electro-magnetic rotation. The central pil-
.ar supports a piece of thick copper wire, which, on the one
side, dips into the mercury contained in a small glass cujr 'A
To a pin at the bottom of this cup a small cylindrical magnet
is attached by a thread, so that one pole shall rise a little above
i.he surface of the mercury, and be at liberty to move around
Mi<! wire. Tlu> bottom of the cup is perforate!, nnd hup a cop*


16Q -

per pin passing through it, which, touching the mercury on the
inside, is also in contact with the wire that proceeds outward?.
' n that side of the in-
i .{.rumen t. On the other
bide of the instrument t>,
the thick copper wire,
soon after turning down,
terminates, but a thinnci
piece of wire forms a
communication between
it and the mercury on
the cup beneath. As
freedom of motion is re-
garded in the wire, it is made to communicate with the formci
by a ball and socket-joint, the ball being held in the socket by
a thread ; or else the ends are bent into hooks, and the one is
then hooked to the other. As good metallic contact is required,
the parts should be amalgamated, and a small drop of mercury
placed between them; the lower ends of the wire should also be
amalgamated. Beneath the hanging wire a small circular mag-
net is fixed in the socket of the cup , so that one of its poles
is a little above the mercury. As in the former cup, a metallic
connexion is made through the bottom, from the mercury to the
external wire.

If now the poles of a battery be connected with the horizon-
tal external wires c c, the current of electricity will be through
the mercury and the horizontal wire, on the pillar which con
nects them, and it will now be found that the movable part of
the wire will rotate around the magnetic pole in the cup b, and
the magnetic pole round the fixed wire in the other cup a, in the
direction before mentioned.

By a very delicate apparatus, the magnetic pole oi the
earth may be made to put the wire in motion.

Kjrtfoiii Pi* 1161. Fig. 167 represents another ingenious

Ki<. contrivance, invented by M. Ampere for illus-


tratiiig the electro-magnetic rotation ; and it has the advantage
of comprising within itself the voltaic combination which is
employed. It consists of a cylinder of copper
about two inches high, and a little less than two
inches internal diameter, within which is a small
cylinder, about one inch in diameter. The two
cylinders are connected together by a bottom,
having an aperture in its centre the size of the
smaller cylinder, leaving a circular cell, which
may be filled with acid. A piece of strong cop-
per wire is fastened across the top of the inner
cylinder, and from the middle of it rises, at a
right angle, a piece of copper wire, supporting a
very small metal cup, containing a few globules of mercury. A
cylinder of zinc, open at each end, and about an inch and a
quarter in diameter, completes the voltaic combination. To the
latter cylinder a wire, bent like an inverted U, is soldered at
opposite sides ; and in the bend of this wire a metallic point is
fixed, which, when inserted in the little cup of mercury, sus-
pends the zinc cylinder in the cell, and allows it a free circular
motion. An additional point is directed downwards from the
contra! part of the stronger wire, which point is adapted to a
small hole at the top of a powerful bar magnet. When the
apparatus with one point only is charged with diluted acid, and
set on the magnet placed vertically, the zinc cylinder revolves
'n a direction determined by the magnetip pole which is upper-
most. With two points, the copper revolves in one direction
and the zinc in a contrary direction.

1162. If, instead of a bar magnet, a horse-shoe magnet be
employed, with an apparatus on each pole similar to that which
has now been described, the cylinders in each will revolve in
apposite directions. The small cups of mercury mentioned in
the preceding description are sometimes omitted, and the points
are inserted in an indentation on the inverted U.


How is the mag 1163. The magnetizing power of the con-
o/lhe n Kry r ductin g * of a Battery is very greatly in-
increased f creased by coiling it into a helix, into which
the body to be magnetized may be inserted. A single cir-
cular turn is more efficient than a straight wire, and each
turn adds to the power within a certain limit, whether the
whole forms a single layer, or whether each successive turn
encloses the previous one.*

How is a Mix 1164 ' When a helix of S reat P wer is
of great power required, it is composed of several layers of

obtained? . mu **". -i t v

wire. Ihe wire terming the coil must be

insulated by being wound with cotton, to prevent any lat-
eral passage of the current.

1165. Fig. 168 represents a helix on a stand.
A bar of soft iron, N S, being placed within
tbe helix, is connected with the battery- bv

Fig. 168.

Fig. 168.

* The amount of power dereloped by electro-magnets depends, when the
size of the magnet and its envelope of wire is suitable, upon the amount of
zinc consumed in the battery. Much controversy has been held about the
possibility of so employing electro-magnetism as to substitute it economic-
ally as a motive force for those agents now employed viz., steam, water,
and air. The attempts thus far have been, unsuccessful. Although many
machines have been devised whose propelling force was electricity or olec-
tro-magnetiRm, the cost of their propulsion was far greater than by any
other plan in use.


tncans of the screw-cups on the base of the stand. The two
extremities of the bar instantly become strongly magnetic, and
keys, or pieces of iron, iron filings, nails, &c., will be held up
so Jong as the connexion with the battery is sustained. But, so
soon as the connexion is broken, the bar loses its magnetic
power, and the suspended articles will fall. The bar can be
made alternately to take up and drop such magnetizable articles
as are brought near it, as the connexion with the battery is
made or broken.

1166. A steel bar placed within the helix acquires the polar-
ity less readily, but retains it after the connexion is broken.
Small rods or bars of steel, needles, &c., may be made perma
nent magnets in this way.

1167. A bar temporarily magnetized bv
What is an Etec- . , , . . . n , r ,,
tro-ma'rnet? " ie electric current is called an Electro-

1168. To ascertain the poles of an elec-

ffow ran the poles . . , , , J ,

of an electro- tro-magnet, it must be observed that the
magnet be dis- north pole will be at the furthest end of
the helix when the current circulates in
the direction of the hands of a watch.

1169 Magnets of prodigious power have been formed by
mean- 1 of voltaic electricity.

\Vliat was the H70. An electro-magnet was constructed by
ptnt-KT of the Professor Henry and Dr. Ten Eyck which was

electro-magnets capal)]e O f supporting a weight of 750 pounds.

constructed .v/ L

Prof. Henry They have subsequently constructed another,

and ^ Dr. Ten w hi c h will sustain 2063 pounds. It consists of
a bar of soft iron, bent into the form of 2
horse-shoe, and wound with twenty-six strands of copper bell-
wire, covered with cotton threads, each thirty-one feet long ;
about eighteen inches of the ends are left projecting, so that
only twenty-eight feet of each actually surround the iron. The
aggregate length of the coils is therefore 728 feet. Each strand


is ^ound on a little less than an inch ; in the middle of the
horse-shoe it forms three thicknesses of wire ; and on tho ends,

Online LibraryRichard Green ParkerA school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of → online text (page 27 of 38)