salt or oxide, having a metallic base, forms part of the electric
circuit, and, by the electrical action, the oxygen or acid will be
drawn to the positive end of the circuit, while the pure meta)
vill be forced to the negative pole, where it will either combine
382 NATURAL PHILOSOPHY.
with the metal or adhere to it, taking its exact form. The
thickness of the coating of the pure metal will depend on tiw
length of time that the body to be coated is subjected to the
combined action, chemical and electrical. Hence a mere film
or a solid crust may be attached to any conducting substance.
When a substance not in itself a conductor is to be coated, it
must first be made a conductor by covering its surface with
some substance which will impart the conducting power. This
is usually effected by means of finely-powdered black lead.
1195. When a part only of a body is to be coated by tho
electrotype process, the parts which are to remain uncoate^ must
previously be protected by means of a thin covering of wax,
tallow or some other non-conducting substance.
1196. MAGNETO-ELECTRICITY. Mag-
What is Mag- , A . .^ f . , ,
neto-electridty? neto- electricity treats of the development
of electricity by magnetism.
How is Mag- 1197. Electric currents are excited in a
neto-electridty conductor of electricity by magnetic changes
developed? . , . , . . . . . m , ?L
taking place in its vicinity. Thus, the
movement of a magnet near a metallic wire, or near an iron
bar enclosed in a wire coil, occasions currents in the wire.
1198. When an armature, or any piece of soft iron, ia
brought into contact with one or both of the poles of a magnet,
it becomes itself magnetic by induction, and by its reaction
adds to the power of the magnet : on the contrary, when
removed from the contact, it diminishes the power of the mag-
net, and these alternate changes in its magnetic state induce a
current of electricity.
1199. The most powerful effects are obtained
b ? cauain g a bar of soft iron ' enclosed in a
ffects of mag- helix, to revolve by mechanical means near the
wto-ekctncity p i eg O f a stee j ma g ne t. As the iron approaches
the poles in its revolution, it becomes mag-
netic; as it recedes from them, its magnetism disappear* ; *md
MAGNETO- ELECTRICITY .
this alternation of magnetic states causes the flow of a current
of electricity, which may be directed in its course to screw-
cups, from which it may be received by means of wires con-
nected with the cups.
1200. TIIE MAGNETO-ELECTRIC MACHINE.-
* Fig. 181 represents the magneto-electric ma-
chine, in which an armature, bent twice at
right angles, is made to revolve rapidly in front of the poles of
a compound steel magnet of the U form. The U magnet, whose
aorth pole is seen at N, is fixed in a horizontal position, with its
poles as near the ends of the armature as will allow the latter
to rotate without coming into contact with them. The armature
is mounted on an axis, extending from the pillar P to a small
pillar between the poles of the magnet. Each of its legs is
enclosed in a helix of fine insulated wire. The upper part of
the pillar P slides over the lower part, and can be fastened in
tiny position by a binding screw. In this way the band con-
necting the two wheels may be tightened at pleasure, by in-
creasing the distance between them. This arrangement aLso
renders the machine more portable. By means of the multiply-
ing- wheel W, which is connected by a band with a small wheel
on the axis, the armature is made to revolve rapidly, so that
the magnetism induced in it by the steel magnet is alternately
;*&! NATUKAL PHILOSOPHY.
ilfi&troyed and renewed in a reverse direction to the previous
jne. When the legs of the armature are approaching the mag-
net, the one opposite the north pole acquires south polarity, and
the other north polarity. The magnetic power is greatest while
the armature is passing in front of the poles. It gradually
diminishes as the armature leaves this position, arid nearly dis-
appears when it stands at right angles with the magnet. A*
each leg of the armature approaches the other pole of the U
magnet, by the continuance of the motion magnetism is again
induced in it, but in the reverse direction to the previous one.
These changes in the magnetic state of the armature excite
electric currents in the surrounding helices, powerful in proper
tion to the rapidity with which the magnetic changes are pro-
1201. Shocks may thus be obtained from the machine, and, if the
motion is very rapid, in a powerful machine the torrent of shocks
becomes insupportable the muscles of the hands which grasp the
handles are involuntarily contracted, so that it is impossible to
loosen the hold. The shocks, however, are instantly suspended by
bringing the metallic handles into contact.
1202. THERMO-ELECTRICITY. Thermo-
What is Thar- , , . . f , - . .
no-electricity? electricity expresses a form of electricity
developed by the agency of heat.
1203. In the year 1822, Professor Seebeck, of Lorlin, dis-
covered that currents of electricity might be produced by the
partial application of heat to a circuit composed exclusively of
soJ.id conductors. The electrical current thus excited has been
termed Thermo-electric (from the Greek Thermos, wbich signi-
fies heat), to distinguish it from the common galvanic current;
which, as it requires the intervention of a fluid element, was
denominated a Hydro-electric current. The term Stereo-electric
current has also been applied to the former, in order to mark
its being produced in systems formed of solid bodies alone. It
is evident that if, as is supposed in the theory of Ampere, mag-
nets owe their peculiar properties to the continual circulation
of electric currents in their minute parts, these currents will
<\)iue under the description of the stereo-electric currents
TH UXMO ELECTRICITY.- -A8TKOM OMY. rfSfi
1204. From the views of electricity which have now been
given, it appears that there are, strictly speaking, three state*
of electricity. That derived from the common electrical ma-
chine i& in the highest degree of tension, and accumulates until
it is able to force its way through the air, which is a perfect
non-conductor. In the galvanic apparatus the currents have a
smaller degree of tension; because, although they pass freely
through the metallic elements, they meet with some impedimenta
in traversing the fluid conductor. But in the thermo-electric
currents the tension is reduced to nothing ; because, throughout
the whole course of the circuit, no impediment exists to its free
and uniform circulation.
1205. If the junction of two dissimilar metals be heated, an
electrical current will flow from the one to the other.
1206. Instead of two different metals, one metal in differen*
Conditions can be used to excite the current.
1207. Metals differ greatly in their power to excite a cur-
rent when associated in thermo-electric pairs. A current may
be excited with two wires of the same metal, by heating the
end of one, and bringing it into contact with the other. Thi?
experiment is mostr-successful when metals are used that have
the lowest conducting power of heat.
1208. Thermo-electric batteries have been constructed with
sufficient power to give shocks and sparks, and produce various
magnetic phenomena, indicative of great magnetic power ; but
the limits of this volume will not allow a further consideration
of the subject.
1209. ASTRONOMY. Astronomy treats
What is Aslron- r> L , -\ i i -i ^i i
omy i of the heavenly bodies, the sun, moon, plan-
ets, stars and comets, and of the earth as a
member of the solar system.
1210. The study of astronomy necessarily involves an acquaint-
ance with mathematics, but there are many interesting facts, which
have Leen fully established by distinguished astronomers, whicb
ought to be familiar to those who huve neither the opportunity nor
d8(.' NATURAL PHILOSOPHY.
tJio leisu/e to pursue the subject by the aid of mathematical light.
To such the following brief notice of the subject will not be devoid
1211. Some of the most distinguished men who
Who are some have contributed to the great mass of facts and
tf the most dis- laws which make up the science of Astronomy
tinguished As- were Hipparchus, Ptolemy, Pythagoras, Coperni-
tronomers ? cus, Tycho Brahe, Galileo, Kepler and Newton,
The present century has added to this list many
other* whose fame will descend to posterity with great lustre.
1212. Hipparchus is usually considered the father of Astronomy.
He was born at Nicaea, and* died about a hundred and twenty-five
years before the Christian era. He divided the heavens into con-
stellations, twelve in the ecliptic, twenty-one in the northern, and
sixteen in the southern hemisphere, and gave names to all the stars.
He discovered the difference of the intervals between the utinn-
nal and vernal equinoxes, and, likewise, by viewing a tree on a
plain, and noticing its apparent position from different places of
observation, he was led to the discovery of the parallax of the heav-
enly bodies ; that is, the difference between their real and apparent
position, viewed from the centre and from the surface of the earth.
He determined longitude and latitude, fixing the first degree of lon-
gitude at the Canaries.
1213. Ptolemy nourished in the second century of the Christian
era. He was a native of Alexandria, or Pelusium. In his system
he placed the earth in the centre of the universe, a doctrine univer-
sally adopted and believed until the sixteenth century, when it was
confuted and rejected by Copernicus. Ptciemy gave an account of
the fixed stars, and computed the latitude and longitude of one thou-
sand and twenty-two of them.
1214. Pythagoras was born at Samos, and his death is supposed
to have taken place about five hundred years before the Christian
era. He supposed the sun to be the centre of the universe, and
that the planets revolved around him in elliptical orbits. This doc-
trine, however, was deemed absurd until it was established by Co-
pernicus in the sixteenth century.
1215. Tycho Brahe, a Danish astronomer, flourished about the
middle of the sixteenth century. His astronomical system was sin-
gular and absurd, but the science is indebted to him- for a more cor-
rect catalogue of the fixed stars, and for discoveries respecting the
motions of the moon and the comets, the refraction of the rays of
light, and for many othei important improvements. To him, also,
was Kepler indebted for the principal facts which were the basis of
nis astronomical labors.
1216. Copernicus v~<is born in Prussia, in the latter part of the
fifteenth century. Ho revived the system of Pythagoras, which
placed the sun in the centre of the system. He taught the true
doctrine that the aarent motion of the heavenl bodies is caused
apparent motion of the heavenly
n of the earth. But, for
publication of his system, lie gained but
by the real motion of the earth. But, for nearly a century after
the publication of his sstem, lie gained but few followers.
1217 Galileo, a native of Pisa, flourished in the latter part of
the pixteenth century. By his observation of the planets Venus and
j upiter, he gained a decisive victory for the Copermcan system. He
rfjis persecuted and imprisoned by the inquisition for holding what
was thought, in that age of ignorance and superstition, to be heret-
ical opinions, and compelled on his knees to abjure the truths
whi :h he had discovered, and which he had too much sense to dis-
believe. Notice has already been taken of this distinguished phi-
losopher in connexion with the laws of falling bodies (see page 52),
for tii-D discovery of which the world is indebted to him.
1213. Kepler, who, from his great discoveries, is called the legis-
ator of the heavens, was a native of Wirtemberg, in 1571. Availing
himself of the observations of Tycho Brahe, he discovered three
great laws, known as Kepler's laws of the planetary motions, and on
them were founded the discoveries of Newton, as well as the whole
modern theory of the planets.
Kepler's laws could not have been discovered but for the observa-
tions of Tycho Brahe (as Kepler was not himself an observer), and
no further discoveries could have been made than Kepler made but
for the telescope of Galileo. It has elsewhere been stated that
Galileo was indebted to Jansen, of Holland, for the idea of the
telescope. But. since the days of Galileo, the telescope has been
most wonderfully improved, and invested with almost inconceivable
powers. Herschel computed that the power of his telescope was so
great as to penetrate a space through which light (moving with the
prodigious velocity of 200,000 miles in a second of time) would
require 350,000 years to reach us. But the great telescope of Lord
Rosse would probably reach an object ten times more remote.
1219. Sir Isaac Newton, who has been called the Creator of
Natural Philosophy, was born in Lincolnshire, England, in 1642.
His discovery of the universal law of gravitation, and many other
valuable and important contributions which he made to science.,
place him among the foremost of those to whom the world is in-
debted for an insight into the magnificent displays of the material
1220. According to the system of As-
Crtve an ac-
count of the tronomy which is now universally adopted,
wlar system as ^ sun > ^ tre of & system O f heavenly
now adopted. J
bodies, called planets, which revolve around
him as a centre.
Secondly. The earth is one of these planets.
Thirdly. Some of these planets are attended by satel-
lites or moons, which revolve around their respective
planets, and with them around the sun.
338 KATUBAL PHILOSOPHY.
Fourthly. The size, distance and rapidity of motion of
each of these planets is known to be different.
Fifthly. The stars are all of them suns, with systems
of their own, and probably many, if not all of them,
having planets, with their moons revolving around them
Sixthly. There is a central point of the universe, around
which all systems revolve.
Whatismeant 1221 F THE S LAR SYSTEM.-By the
by the Solar Solar System is meant the sun and all the
System? heavenly bodies which revolve around it.
These are the planets with their satellites or moons, our
earth with its moon, together with an unknown number
What are 1222 - OF THE PRIMARY PLANETS. Those
Primary bodies which revolve around the sun, with-
Planete? out rev olving, a t the same time, around
some other central body, are called Primary Planets.
1223. For many years the planets were con-
Gwethenames u i
of the eight sidered to be six in number only, and they were
primary all, except our earih, named after the gods Oi
planets. heathen mythology, Mercury, Venus, Earth,
Mars, Jupiter, and Saturn. In the year 1781, Sir William
Herschel discovered another, to which the name of Uranus has
been given; an<^ in the year 1846 an eighth was discovered, to
which the nan e of Le Verrier was at first given, from a dis-
tinguished Fr-^i ch astronomei, by moans of whom it was pointed
out. It is now known by the name of Neptune.
How many 1224. Besides these primary planets, it was
minor pri- discovered, between the years 1800 and 1807,
mary planets , /
have been dis- that between Mars and Jupiter there were TOUT
covered? smaller planets, of such diminutive size, compared
with the others, that they were called Asteroids. Since the year
1845 one hundred and nine more have been discovered, so that
there are now known to be no fewer than one hundred and
thirteen asteroids, or minor planets, between the orbits of Mars
1225. THE MINOR PLANETS. The following is a catalogue
of the minor planets at present known, arranged in the order
of their discovery, together with the other known planets of out
solar system :
Nime and Number by which
the Minor Planets are known.
Date of Discovery.
Names of Discoverers.
1 Ceres . . .
1801.. Jan. 1 .
Piazzi, of Sicily.
1 802.. March 28...
Gibers, of liromoii.
1804. .Sept. 1
1807.. March 29..
1845.. Dec. 8
1847. .July 1
1 1 en eke, of Germany.
1847.. August 13...
1847. .Got 18
Hind, of London.
1848.. April 26
Graham, of Ireland
1849 April 12
1850.. May 11 ...
1850 Sept 18...
1850.. Nov. 2
1851.. May 19...
1851.. July 29
1852 March 17
1852.. April 17
Luther, of Germany.
1852 June 25
1852.. August 22...
1852.. Sept. 19
1852 Nov 15
22. Calliope ..
lS52..Nov 16 .
23. Thalia *....
1852.. Deo. 15
1853 April 5
1S53 April 6
1853 May 5
1 854.. March 1
1S54 March 1
1854.. July 22
1854.. Sept 1..:...
1854 Get 9 8
Ferguson, of Washington.
1854 .Get 28 ...
1855.. April 14
1855.. April 27.
Sir William Ilerschel.
1846.. Sept 23... -j
Dr. Galle, of Berlin, by d'reo
tion of Le Verrier, of Paris.
The 112th asteroid was discovered in September, 1870. The 113th, in
March ; the 114th, in July, 1871. The honor of many late discoveries of
these bodies rests with Frof. Watson of this country.
NATDKAL 1H1J/)S< >l'H V.
What is the 1%2G. The name planet properly means
tiifftrence be- a wandering star, and was given to this
tween a planet c l ass o f the heavenly bodies because they
and a star? ,, . , ., t , . ,.
are constantly moving, while those bodies
wfcich are called fixed stars preserve their relative posi-
tions. The planets may likewise be distinguished from
the fixed stars by the eye by their steady light, while
ilic fixed stars, on the contrary, appear to twinkle.
1227. The sun, the moon, the planets, and the fixed stars,
which appear to us so small, are supposed to be large worlds,
of ; arious sizes, and at different but immense distances from us.
The reason that they appear to us so small is, that on account of
their immense distances they are seen under a small angle of vision.
Whatuniver- 1228. It has been stated, in the early pages
sallow keeps of this book, that every portion of matter is at-
^r a ^f tracted b y y other p rtion ' and * tha
bodies in their force of the attraction depends upon the quantity
places? O y ma f( er an d the distance. As attraction is
mutual, we find that all of the heavenly bodies attract the
earth, and the earthr likewise attracts all of the heavenly bodies.
It hr.s been proved that a body when actuated by several forces
will be influenced by each one, and will move in a direction
between them. It is so with the heavenly bodies ; each one of
them is attracted by every other one ; and these attractions are
BO nicely balanced by creative wisdom, that, instead of rushing
together in one mass, they are caused to move in regular paths
Ccalled orbits) around a central body, which, being attracted in
different directions by the bodies which revolve around it, will
its^f revolve around the centre of gravity of the system. Thus,
the sun is the centre of what is called the solar system, and the
planets revolve around it in different times, at different dis-
tances, and with different velocities.
1229. The paths or courses in which the
P lanets move arounJ the sun are called
All of the heavenly bodies move in conic sections,* namely, itf
circle, the ellipse, tins parabola and the hyperbola.
What is meant 1230. In obedience to the universal law of
by a year . gravitation, the planets revolve around the
sun as the centre of their system ; and the time that each
one takes to perform an entire revolution is called its year
Thus, the planet Mercury revolves around the sun in 87
of our days ; hence a year on that planet is equal to 87
days. The planet Venus revolves around the sun in 224
days ; that is, therefore, the length of the year of that
planet. Our earth revolves around the sun in about ^65
days and 6 hours. Our year, therefore, is of that length.
1231. The length of time that each planet take.* in perform-
ing its revolution around the sun, or, in other words, the length
of the year on ea>a planet, is as follows. (The fractional
parts of the day are omitted.} In the same connexion will also
be found the mean distance of each planet from the sun. -ind
the time of revolution arcur.d its axis , or, in other words the
length of the day on each.
Length of the Year in
Mean distance from
in millions of Miles.
Length of lb
Day in Hours
1 Ceres . ..
15. Eunomla _
* Conic sections are curvilinear figures, so called because they can all be
formed by cutting a cone in certain directions. If a cone be cut perpendicu-
lar to its axis, the surface cut will be a circle. If cut oblique to the axis,
the surface cut will be an ellipse. If cut parallel to the slope of the cone,
the section will be a parabola. If cut parallel to the axis, the section will ba
Length of the Year
Mean Distance from
the Sun in millions
Lentil of iba
Dav in HOM*
18. Mel ( H.nione
20. Ma-^ilia . .
85. f -
Give an ac-
The sun turns on its axis in about 26 days and 10 hours.
1232. There is a very remarkable law, dis-
covered by Professor Bode, founded, it is true,
on no known mathematical principle, but which
has been found to accord so exactly with other calculations,
that it is recognized as Bode's law for estimating the distance
of the planets from the sun. Thus :
Write the arithmetical progression,
0, 3, 6, 12, 24, 48, 96, 192, 384.
To each of the series add 4, and we have the sums,
4, 7, 10, 16, 28, 52, 100, 196, 388,
which will represent very nearly the comparative distance of
each planet. Now, the distance of the earth from the sun is
92 millions of miles, and as that distance is represented in the
progression by 10, it follows that the distance of Mercury is 7 * 6
of 92 millions, of Venus ^g, &c.
Wh tied t 1233. It is to be observed, however, that before
the discovery tne discovery of the minor planets, there was a
of the minor very remarkable interval between the planet. 1
Jupiterj and that Bode > s law/
to accord with the ^distance of all the other planets,
appeared here to fail in its application. Kepler had suspected
that an undiscovered planet existed in the interval ; but it was
not certainly known until a number of distinguished observers
assembled at Lilienthal, in Saxony, in 1800, who resolved to
direct their observations especially to that part of the heavens
where the unknown planet was supposed to be. The result of
the labors of these observers, and others who have followed
them, has been the discovery of the one hundred and thirteen