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 26 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 26 of 38)
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fixed by a thumb-screw and an insulating piece of ivory to the


arm proceeding from the zinc cylinder. The amalgamated z:nc
if not acted upon by the diluted sulphuric acid until the circuit
of the battery is completed. But, as the nitric acid will filter
through the porous cell, and act upon the zinc, it is advisable to
remove the zinc from the acid when the battery is to remain
inactive. The action of Grove's battery may be considered as
three times greater than that of the sulphate of copper battery.
What are the 1083. The spark from a powerful voltaic bat-
effecls of a pow- tery acts upon and inflames gunpowder, char-

erful voltai- bat- coalj cotto n , and other inflammable bodies, fuses

tery? . ; .. .. , ,

all metals, ourns up or disperses diamonds and

other substances on which heat in other forms produces little or
no effect.

1084. The moat striking effects of Galvanism on the human
frame, aftor death, were exhibited at Glasgow, a few years ago.
The subject on which the experiments were made was the body of
the murderer Clydesdale, who was hanged at that city. He had
Deen suspended an hour, and the first experiment was made in
about ten minutes after he was cut down. The galvanic battery
employed consisted of 270 pairs of four-inch plates. On the appli-
cation of the battery to different parts of the body, every muscle
was thrown into violent agitation ; the leg was thrown out with
great violence, breathing commenced, the face exhibited extraordi-
nary grimaces, and the finger seemed to point out the spectators.
Many persons were obliged to leave the room from terror or sick-
ness ; one gentleman fainted, and some thought that the body had
really come to life.

1085. The wires, by which the circuit of the
How are the ' J

hands protected battery is completed, are generally covered with

when using a gutta-percha, in order that they may be held or
lattery ?

directed to any substance.

(n what respects 1086 ' There are three F inci P al circum -
loes the electric- stances in which the electricity produced by

ity produced by the ga i va nic or voltaic battery differs from
the galvanic bat- , ,

iery differ from tnat obtained by the ordinary electrical ma-

ihat obtained by chine ; namely,

the machine ? ^ The yery bw degree of intenslfy of tnat

produced by the galvanic battery, compared with that obtained
h\ the machine


1087 By inte7isity is here meant something analogous to
what is implied by density as applied to matter ; but in the ono
case it is a ponderable agent, in the other an imponderable, so
that a strict analogy cannot be made out between them. The
term density cannot be applied to any of the imponderable
agents, light, sound, heat or electricity. We speak of the in-
tensity of light, an intensity of heat, &c. Hence, the word
intensity is properly applied to electricity, and we speak of its
tension, instead of its density.

Which will de- The quant i t y O f electricity obtained by gal-
velop the great- ..... ,

er quantity of vamc action is much greater than can be

electricity, the obtained by the machine; but it flows, as it
ft3 were, in narrow stream, '

The action of the electrical machine may be compared to a mighty
torrent, dashing and exhausting itself in one leap from a precipitous
height. The galvanic action may be compared to a steady stream,
supplied by an inexhaustible fountain. In other words, the mo-
mentum of the electricity excited by galvanism is less than that
from the electrical machine ; but the quantity, as has been stated.
is greater.

(2.) The very large quantity of electricity which is set in mo-
tion by the voltaic battery ; and,

(3.) The continuity of the current of voltaic electricity, and
its perpetual reproduction, even while this current is tending to
restore the equilibrium.

1088. Whenever an electrical battery is charged, how great
soever may be the quantity that it contains, the whole of the
power is at once expended, as soon as the circuit is completed.
Its action may be sufficiently energetic while -it lasts, but it is
exerted only for an instant, and, like the destructive operation
of lightning, can effect during its momentary passage only sud-
den and violent changes, which it is beyond human power to
regulate or control. On the contrary, the voltaic battery con-
tinues, for an indefinite time, to develop and supply vast quan-
tities of electricity, which, far from being lost by returning to
their source, circulate in a perpe f ual tream and with uudiiuiu-


ished force. The effects of this continued current on the bodie>s
subjected to its action will therefore be more definite, and will
be constantly accumulating ; and their amount, in process of
time, will be incomparably greater than even those of the ordi-
nary electrical explosion. It is therefore found that changes ii
the composition of bodies are effected by galvanism which car
be accomplished by no other means. The science of galvanism
therefore, has extended the field and multiplied the means ot
investigation in the kindred sciences, especially that of Chem

1089. A common electrical battery may bo
char g ed from a voltaic battery of sufficient

sion manifested size ; but a battery constructed of a small num-
in the galvanic b er O f pairs, even though the plates are large,
furnishes no indication of attraction or repul-
sion equal to that which is given by the feeblest degree of
excitation to a piece of sealing-wax. A galvanic battery con-
sisting of fifty pairs of plates will affect a delicate gold-leaf
electrometer; and, with a series of one thousand pairs, even
pith balls are made to diverge.

1090. The effect of the voltaic pile on the
On what does ,11 .

the effect of the animal body depends chiefly on the number of

voltaic battery plates that are employed; but the intensity of
e ? en the spark and its chemical agencies increase

more with the size of the plates than with their number.

1091. Galvanism explains many facts in
Mention some of

the familiar ef- common life.

fects ofgalvan- Porter, ale, or strong beer, is said to have a
peculiar taste when drunk from a pewter ves
sel. The peculiarity of taste is caused by the galvanic circle
formed by the pewter, the beer, &c., and the moisture of the
under lip.

Works of metals the parts of which are soldered together
soon tarnish in the places where the metals are joined.

Ancient coins composed of a mixture of metal have cruiu-


bled to pieces, while those composed )i pure metal have been

The nails and the copper in sheathing of ships are soon
corroded about the place of contact. These are all the effects
of galvanism.

There are persons wno profess to be able to find out seams in
brass and copper vessels by the tongue which the eye cannot
discover ; and, by the same means, to distinguish the base mix-
tures which abound in gold and silver trinkets.

1092. From what has now been stated, it will be seen that
the effects of galvanic action depend on two nrcumstances ;
namely, 1st, the size of the plates employed ii i the circuit ;
and, 2dly, the number of the pairs constituting a battery. But
there is a remarkable circumstance to be noticed in this con-
nexion ; namely, that there is one class of facts dependent on
the extension of the size of the plates, and
On what does another on the increase of their number. The
the power of a f deve i op fa at and 7nagne tism is de-

battery to pro- e
auce heat and to pendent on the size of the plates, that is, on the

affect the animal ex t en t of the surface acted upon by the chem-

system respect- . .. .

ively depend ? lca * a g en ^ J while the power to decompose

chemical compounds, and to affect the animal
system, is affected in a greater ratio by the increase of the
number of the pairs.

1093. The name Color imotor (that is, the

heat ^ WaS a PP lied bv Dr ' Hare ' of
Philadelphia, to a very powerful apparatus which

he constructed, with large plates, and which he found possessed
of a very remarkable power in producing heat. Batteries con-
structed for this purpose usually consist of from one to eight
pairs of plates. They are made in various forms; sometime?
the sheets of copper and zinc are coiled in concentric spirals,
sometimes placed side by side ; and they may be divided into a
great number of small plates, provided that all the zinc plates
are connected together, and all tlie copper plates together, and


then tho.t the experiments are performed in a channel oj com*
munication, opened between the SETS OF PLATES, and not between
PAIIIS, as in the common battery ; for it is immaterial whether
one large surface be used, or many small ones electrically con-
nected together. The effect of all these arrangements, by which
the metallic surface of a single pair is augmented, is to increase
the quantity produced.

1094. The galvanic or voltaic battery is one of the most valuable
acquisitions of modern science. It has proved in many instances
the key by which science has entered into the innermost recesses of
nature, and discovered the secret of many of her operations. It
has, in great measure, lifted the hitherto impenetrable veil that has
concealed the mysterious workings in the material world, and has
opened a field for investigation and discovery as inviting as it is
boundless. It has strengthened the sight and enlarged the view of
the philosopher and the man of science, and given a degree of cer-
tainty to scientific inquiry hitherto known to be unreached, and sup-
posed to be unattainable ; and, if it has not yet satisfied the hopes
of the alchemist, nor emulated the gold-converting touch of Midas,
it has shown, almost to demonstration, that science may yet achieve
wonders beyond the stories of mythology, and realize the familial
adage that " truth is stranger than fiction

1095. MAGNETISM. Magnetism treata
netiim " aff ~ f tnc properties and effects of the magnet,
or loadstone.

1096. The term loadstone, or, more properly, leadstone, was ap-
plied to an ore of iron in the lowest state of oxidation, from its
attractive properties towards iron, -and its power of communicating
its power to other masses of iron. It received the name of Magnet
from Magnesia, in Asia Minor (now called Guzelhizar) , about fif-
teen miles from Ephesus, where its properties were first well known.
The term magnet is now applied to those substances which, natu-
rally or artificially, are endowed either permanently or temporarilv
with the same attractive power.

1097. Certain ores of iron are found to be naturally pos-
sessed oi magnetic properties, and are therefore called natural
or native magnets, or loadstones. Besides iron and some of the
compounds nickel, and, perhaps, cobalt, also possess magnetic
properties. But al. conductors of electricity are capable of
exerting the magnetic properties of attraction and rcpultdon

while conveying a current of electricity, as will be shown uncLr
the head of Electro-Magnetism.

1098. That part of science which relates to the development of
magnetism by means of a current of electricity will be noticed ufi-
der.the head of Electro-Magnetism, in which connexion will also
be mentioned the development of electricity by magnetism, to which
the term Magneto-Electricity has been applied.

What are the 1099. There are two kinds of magnets,
two kinds of namely, the native or natural magnet, an<3

the artificial.

1100. The native magnet, or loadstone, is an ore of iron,
found in iron mines, and has the property of attracting
*ron, and other substances which contain it.

What is a per- 1101. A permanent artificial magnet is a
manent magnet? piece of iron to which perm anent magnetic

properties have been communicated.


permanent periment, the artificial is to be preferred to

or the artificial ^ u magnet
magnet ?

1103. If a straight bar of soft iron be held in a vertical posi-
tion (or, still better, in a position slightly inclined to the perpen-
dicular, the lower end deviating to the north), and struck several
smart blows with a hammer, it will be found to have acquired,
by this process, all the properties of a magnet; or, in other
words, it will become an artificial magnet.

What are the 1104. The properties of a magnet are,
properties of a polarity ; attraction of unmagnetic iron ; at-

traction and repulsion of magnetic iron ; the
power of communicating magnetism to other iron. Beside*
these properties, the magnet has recently been discovered to be
possessed of electrical properties. These will be considered it
another connexi Dn.

What is the po- 1105. By the polarity of a magnet is meant
larity of a mag- the property of pointing or turning to the

north and south poles. The end which points


to the north is called the north pole of the magnet, and the
other the south pole.

1106. The attractive powor of a magnet is generally stated
to be greatest at the poles ; but the actual poles, or points of
greatest magnetic intensity, in a steel magnet, are not exactly
at the ends, but a little witnm them.

How willa mag- 1107 - When a magnet is supported in
net move when such a manner as to move freely, it will
eeysuspen spontaneously assume a position directed
nearly north and south.

1108. The points to which the poles of a
What are the ., 7 ml
magnetic poles / magnet turn are the magnetic poles. These

do not exactly coincide with the astronomical
poles of the earth ; but, although the value of the magnetic
needle has been predicated on the supposition that its polar-
ity is a tendency to point exactly to the north and south
poles of the earth, the recent discovery of the magnetic
poles, as the points of attraction, has not depreciated the
value of the compass, because the variation is known, and
proper allowances can be made for such variation.

1109. There are several ways of supporting

How are mag- ma g rie t, so as to enable it to manifest its
nets supported]

polarity, first, b,y suspending it, accurately

balanced, from a string. Secondly, by poising it on a sharp
point. Thirdly, by attaching it to some buoyant substance, and
allowing it to float freely on water.

of magnetic "at- 1110. Different poles of magnets attract,
traction and re- and similar poles repel each other.
pulsion ?

There is here a close analogy between the attractive and repul-
sive powers of the positive and the negative forms of electricity,
and the northern and southern polarities of the magnet. The same
law obtains with regard to both ; namely, between like ;>cu?m there
ff rt-pu/siitn, bfjiovn inlikc there is attraction


1111. A magnet, whether native or artificial attracts iron or
which has no magnetic properties ; but it both attracts and

reptls those substances when they are magnetic : that is the
oorth pole of one magnet will attract the south pole of another,
and the south pole of one will attract the north of another ;
but the north pole of the one repels the north pole of the other,
and the south pole of one repels the south pole of another.

1112. If either pole of a magnet be brought near any small
piece of soft iron, it will attract it. Iron filings will sdso adhere
in clusters to either pole.

To what bod- 1113. A. magnet *nay communicate its

ies are the ma - ,. ,, . , v

netic properties properties to other unmagnetized bodies.

most easily com- But these properties can be generally con-
municatcd? > . ,, , .

veyed to no otter substances than iron.

nickel or cobalt, without the aid of electricity.

Coulomb has discovered that " all solid belies are sus-
ceptible of magnetic influence" But the " influence,"
is perceptible only by the nicest tests, and under peculiar

What are per- 1H4. All permanent natural and artificial
manent mag- magnets, as well as the bodies on wt icli they
act, are either iron in its pure state or such
compounds as contain it.

What effect has 1115 - The powers of a magn t are in-
the use of a ma g- creased by action, and are impaired and

net on its -power? 1^.1.1 j-

even lost by long disuse.

TJ-, . . 1116. When the two poles of a magnet are

V\ fiat is a

horse-shoe or brought together, so that the magnet resembles
u ****** in shape a horse-shoe, or the capital letter U,
it is called a horse-slioe magnet, or a U magnet ; and it may
be made to sustain a considerable weight, by suspending
substances from a small iron bar, extending from one pole


to tho other. This bar is called the keeper. A small adr-
ditiui may be made to the weight every d&y.

1117. Soft iron acquires the magnetic power very readily,
And also loses it as readily ; hardened iron or steel acquires
the property with difficulty, b^t retains it permanently.

MTT. < f 77 1118. When a magnet is broken or divided.

What follows

when a mag- each part becomes a perfect magnet, having


net is divided? b()th a north and gouth pole

This is a remarkable circumstance, since the central part of a,
magnet appears to possess but little of the magnetic power;
out, when a magnet is divided in the centre, this very part as-
sumes the magnetic power, and becomes possessed in the one
part of the north, and in the other of the south polarity.

1119. The magnetic power of iron or steel appears to reside
wholly on the surface, and is independent of its mass.
In what do 1120. In this respect there is a strong resem-

magnetism blance between magnetism and electricity. Elec-
and electricity . . A , . ; , ..

resemble each tricity, as has already been stated, is wholly con-

other? fined to the surface of bodies. In a few words,

magnetism and electricity may be said to resemble each other
in the following particulars :

(U) Each consists of two species, namely, the vitreous and
the resinous (or, the positive and negative) electricities ; and the
northern or southern (sometimes called the Boreal and the
Austral) polarity.

(2.) In both magnetism and electricity, those of the same
aamc repel, and those of different names attract each other.

(3.) The laws of induction in both are similar.

(4.) The influence, in both cases (as has just been stated)
resides at the surface, and is wholly independent of their mass.

What effect H21. Heat weakens, and a great degree of
has heat )n heat destroys the power of a magnet ; but the
magnetic attraction is undiminished by the in-
terposition of any bodies, except iron, steel, &c.


ftiuai jtiwr 1122. Electricity frequently changes the

-'"uses will aj poles of a magnet ; and the explosion of a small
feet the polar-

ityofa mag- quantity of gunpowder, on one of the poles.
"d f produces the same effect. Electricity, also,

sometimes renders iron and steel magnetic, which were
not so before the charge was received.

What is the 1123. The effect produced by two magnets,
e foutlemag- use( l together, is much more than double that
net ? of either one used alone.

What is meant 1124. When a magnet is suspended freely
by "the dip- f roin fts centre, the two poles will not lie in

ping of a mag-
net, and hav the same horizontal direction. This is called
ts it corrected? ^ j nc ii nat i on or t he dipping of the magnet.
1125. The tendency of a magnetic needle to dip is corrected,
in the mariner's and surveyor's comp-asses, by making the south
ends of the needles intended for use in northern latitudes some-
what heavier than the north ends. Compass-needles, intended
to be employed on long voyages, where great variations of lati-
tude may be expected, are furnished with a small sliding-weight,
by the adjusting of which the tendency to dip may be counter-
acted. The cause of the dipping of the needle is the superior
attraction caused by the closer proximity of the pole of the mag-
net to the magnetic pole of the earth. In north latitude, the
north pole of the needle dips ; in south latitude, the south pole.

l n w hat direc- 1126. The magnet, when suspended, does not

Han does a invariably point exactly to the north and south

nag-net point . , . ...

when free/y points, but varies a little towards the east or

' l Vended > t h e west This variation differs at different
places, at different seasons, and at different times in the day.
1127. T? e variation of the magnetic needle from what has been
supposed its true polarity was a phenomenon that for centuries
uad baffled the science of the philosopher to explain. Recent
discoveries have given a satisfactory explanation of this apparent


anomaly.* The earth has, in fact, four magnetic poles, two of
which are strong and two are weak. The strongest north pole
is in America, the weakest, in Asia. The earth itself is consid-
ered as a magnet, or, rather, as composed in part of m^gnetie
substances, so that its action at the surface is irregular. The
variation of the needle from the true geographical meridian ii
therefore subject to changes more or less irregular, t
What gift has 1128. The science of Magnetism has rendered
Magnetism i mmense advantages to commerce and navigation,
bestowed on by means of the mariner's compass. The Mari-

navigaticm ? ner's Compass consists of a magnetized bar of steel
What is the . , . fi ,

Mariner's called a needle; having at its centre a cap fitted to

? it, which is supported on a sharp-pointed pivot

* The following statement has been made in the National Intelligencer
on the authority of its London correspondent :

Mr. Faraday, in a late lecture before the Royal Institution upon the
Magnetic Forces, made the following important announcement .

" A German astronomer has for many years been watching the spots on
the sun, and daily recording the result. From year to year the groups of
spots vary. They are sometimes very numerous, sometimes they are few.
After a while it became evident that the variation in number followed ?.
descending scale through five years, and then an ascending scale through
five subsequent years, so that the periodicity of the variations became 8
visible fact.

" While our German friend was b%jr with his groups of sun-spots, a*
Englishman was busy with the variations of the magnetic needle, lie, too.
was a patient recorder of patient observation. On comparing his tabular
results with those of the German astronomer, he found that the variationi
of the magnetic ne>,Jle corresponded with the variations of the sun-spots,
that the years when the groups were at their maximum, the variations of
the needle were at their maximum, and so on through their series. Thia
relation may be coincident merely, or derivative ; if the latter, then do we
connect astral and terrestrial magnetism, and new reaches of science are
open to us."

t The northern magnetic pole on the western continent is in latitude 70
N. and longitude 97 VV. On the eastern continent the pole is about at the
point where the Lena River crosses the Arctic circle. The south poles are
nearly on the Antarctic circle, one in 130 E. longitude, and the other 120
W. from Greenwich. The poles are doubtless slowly swinging about the
poles of the earth. The direction of the needle for the northeast portion of
the North American continent is west of north. A line on winch the needle
points clue north runs through Lake Erie, the eastern pint of Ohio, a c< rner
of Pennsylvania, the District of Columbia, and North Carolina. West of
this line the needle points to the of north. At San Francisco the pres-
ent direction of the needle (1871) is nearly 17 east of north. The line of
no variation is slowly moving westward, and the direction of the needle
over the whole continent is slowly changing in the same direction.



Sxe<\ in the base of the instrument. A. circular plate, or card,
the circumference of which is divider into degrees, is attached
to the needle, and turns with it. On an inner circle of the card
tho thirty -two points of the mariner's compass are inscribed

Fig; 165.

1129. The needle is generally placed under the card of a
mariner's compass, so that it is out of sight; but small needles,
used on land, are placed above the card, not attached to it, and
the card is permanently fixed to the box.

] 130. The compass is generally fitted by two sets of axes to
an outer box, so that it always retains a horizontal position,
even when the vessel rolls. When the artificial magnet or necdU
is kept thus freely suspended, so that it may turn north or south,
the pilot, by looking at its position, can ascertain in what direc-

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 26 of 38)