G. P. (George Payn) Quackenbos.

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

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current is produced on the wire, as is shown by a galvanometer attached to
it. This principle has been applied in different magneto-electric machines,
with which water may be decomposed, platinum wire heated to redness,
sparks produced, shocks given, and other experiments performed.

929. THE MAGNETO-ELECTEIC MACHINE. Fig. 328 rep-
resents one form of the Magneto-electric Machine.

S is a compound horse-shoe magnet supported on three pillars. In front
of its poles, and as near as it can be brought without touching, is a bar of
soft iron bent at right angles, and surrounded with several coils of insulated
copper wire. The ends of this wire are pressed by springs against a con-
Prove that it renders the helix magnetic. What phenomena are exhibited by two
straight wires traversed by electric currents, when brought near each other ?
927. What is Magneto-electricity ? What is said of its phenomena ? 928. What is the
first experiment illustrative of magneto-electricity? The second experiment ? In
what is the principle hero described applied ? 929. Describe the Magneto-electric



MAGNETO-ELECTRIC MACIIINE. 307

Fig. 328.




MAGNETO-ELECTRIC MACHINE.

ducting metallic plate, connected by wires passing under the stand with, the
screw-cups A, B. The soft iron armature just described is mounted on an
axis which is made to revolve by a wheel turned by a handle. The handle
being rapidly turned, each half-revolution of the armature brings its extrem-
ities near opposite poles of the magnet, thus reversing its polarity, and pro-
ducing a strong electric current on the wire. If small copper cylinders
attached to the wires are grasped one in each hand, as shown in the figure,
a series of severe shocks are received, and the muscles are so contracted that
it is almost impossible to open the hands and let go the conductors.

Machines of this kind, adapted to medical use, have been found effica-
cious in cases of rheumatism, dyspepsia, sprains, nervous diseases, &c., the
current being made to pass through the diseased part.



930. Experiments with powerful electro-magnets show
that almost all substances are susceptible of magnetic in-
fluence. Some are attracted by the magnet ; others, re-
pelled ; while a few are not acted on at all, though when
more powerful magnets shall bo made they may perhaps
be found to fall under one of the two previous classes.

Hence arises a three-fold division of bodies. 1. Mag-
netic bodies, or such as are attracted by an electro-magnet.

Machine represented in Fig. 823, and its mode of operation. What is the effect of
such a machine on the human system ? What use has been made of machines of this
kind? 930. What has been shown by experiments with powerful electro-magnets?
Name tho three classes into -which bodies are divided with reference to the influence



368



DIAMAGNETISM.



2. Diamagnetic, or such as are repelled,
such as are not acted on at all.

Fig. 329.



3. Indifferent, or



The difference between these three classes
of bodies may be illustrated with the apparatus
shown in Fig. 329. N, S, are the poles of an
electro-magnet, which is connected by the wires
C, Z, with a galvanic battery. A bar of iron,
nickel, cobalt, manganese, or other magnetic
substance, suspended between the poles so as to
move freely, will come to rest with its ends as
near them as possible, in the position II. On
the contrary, a bar of bismuth, phosphorus, zinc,
tin, or other diamagnetic substance, similarly
suspended, will be repelled and come to rest at right angles to the position
just described, as shown by the dotted line, with its sides opposite the poles
of the axis and its ends as far from them q,s possible. Similar attraction and
repulsion are exhibited if the substances are presented to either pole sepa-
rately. An indifferent substance will remain in any position in which it is
placed, being neither attracted like the iron nor repelled like the bismuth.

Similar experiments may be made on liquids and gases by enclosing them
in tubes. It is thus found that oxygen is magnetic ; water, alcohol, ether,
and the oils, diamagnetic.




CHAPTER XVIII.

ASTRONOMY.

931. ASTRONOMY is the science that treats of the heav-
enly bodies, their motions, size, distance, &c.

By the heavenly bodies are meant the sun, the moon,
stars, planets, and comets.

932. Astronomy, as it is the most sublime, is also the oldest of sciences.
The shepherds of the patriarchal age, tending their flocks by day and night
beneath the canopy of heaven, naturally directed their gaze to the brilliant



xerted on them by electro-magnets. Define each. Illustrate the difference be-
tween these three crosses with the apparatus represented in Fig. 329. How may sim-
ilar experiments bo made on liquids and gases ? What gas is found to bo magnetic ?
What liquids are diamagnetic ?

931. What is Astronomy? What are meant by the heavenly bodies ? 932. Who



ASTRONOMY. 369

orbs with which it is studded, observed their motions, and thus became the
first astronomers. Chaldean observations are said to extend back to within
a hundred years of the flood. The Chinese, also, paid great attention to this
science in remote antiquity. We are told that more than 2,000 years before
the birth of Christ, an emperor of Clu'na put to death his two chief astrono-
mers for not predicting an eclipse of the sun.

Destitute of the admirable instruments which modern science has pro-
duced and used with signal success, the ancient astronomers of course erred
in many of their conclusions. We can only wonder that they obtained as
much knowledge as they did respecting the heavenly bodies.

933. To unfold the principles of astronomy at length
would require a volume, and to understand them thorough-
ly, a knowledge of the higher mathematics is essential. We
can here present only such leading facts as will serve to
give a general view of the science.

934. FUNDAMENTAL FACTS. The great facts established
by the researches of astronomers are as follows :

1. Space is filled with worlds.

Looking up into the heavens on a clear night, we see them all around us.
The telescope reveals millions. There are no doubt millions more too remote
to be seen at all, and others which from being non-luminous escape our vis-
ion. Powerful instruments reach to points from which light, travelling as it
does with the enormous velocity of 192,000 miles in a second, would be 60,000
years in reaching us, and throughout the whole of this vast field worlds are
everywhere scattered. We can but infer that the regions to which man's eye
has never penetrated are similarly studded ; and that, if an observer could
be transported to the remotest star visible with his telescope, he would see
spread before him in the same direction a firmament no less rich and splendid
than that which he beheld from the earth.

2. These worlds are divided into systems, the members
of which are bound together by mutual attraction. Each
system has a central sun, round which the other members,
called Planets, revolve. While this revolution is going on,
the suns themselves with their respective planets move
about a common fixed central point.

3. The stars that we see twinkling in the sky are suns.

were the first astronomers ? How far back are Chaldean observations said to extend?
"What story shows the attention paid to astronomy by the Chinese in remote anti-
quity? What is said of the ancient astronomers ? What is the first great fact estab-
lished by astronomers? What facts are stated respecting the number of worlds?
AVhat inference is drawn respecting the regions of space unpenctrated by the eye of
man? How are these Avorlds divided? What are the stars that wo see twinkling
10*



370 ASTEONOMY.

The planets that we suppose to revolve about them are
non-luminous, and therefore invisible.

4. Some of these planets have satellites or moons moving
around them, and with them around the sun of the system
to which they belong.

5. The Earth, which we inhabit, is a planet belonging
to what is known as the Solar System, of which the Sun is
the centre. The Earth is attended by one satellite known
as the Moon.

TEie Solar System.

935. The Solar System, as at present known, consists of
the sun, its centre; seventy planets revolving round it,
of which sixty-two, on account of their small size, are called
Asteroids (starlike bodies) ; twenty moons revolving round
the planets ; and many thousand comets, the exact number
of which is unknown.

936. That the earth and other planets move round the sun, was taught by
the philosopher Pythagoras about 500 B. c. Deceived by appearances, how-
ever, the ancients generally rejected this theory, and believed the earth to be
the fixed centre of motion for all the heavenly bodies. Some made the plan-
ets revolve round the sun, and the sun carrying the planets with it to move
round the earth. The Egyptian astronomer Ptolemy supposed the universe
to consist of a number of hollow spheres arranged one within another, and
appropriated respectively to the sun, the moon, the planets, and the stars.
The earth, according to Ptolemy, was at the centre of these spheres, which
turned round it from east to west every twenty -four hours, carrying the stars
and planets with them ; being of crystal, they were perfectly transparent,
and the inner ones did not therefore obscure the more distant luminaries
seen through them.

These theories, particularly Ptolemy's, prevailed till about the middle of
the sixteenth century, when the Prussian philosopher Copernicus revived the
teachings of Pythagoras, and established what is called from him the Coper-
nican System, which is now acknowledged as the true theory of the universe.
Fearing the prejudices of his fellow-men, Copernicus withheld his system
from them for some years. His great work, in which his views were embod-



in the sky ? Why are not their planets visible ? By what are some of the planets
attended? What is the Earth? By what is it attended? 905. Of what does the
Solar System, as at present known, consist ? 936. What was Pythagoras's theory of
the universe ? What was the belief of the ancients generally ? Give an account of
Ptolemy's theory. By whom and when was the true system revived ? When was



THE SOLAR SYSTEM. 371

led, was finally published ia 1543, just in time for a copy to be placed in his
hands on his death-bed.

The Copernican system at first met with but moderate favor. Its truth,
however, was established by Galileo, whose observations with the newly-
invented telescope afforded him incontrovertible arguments in its favor. Yet
the advocates of the old system were determined to close their eyes. On
Galileo's announcing the discovery of four moons about the planet Jupiter,
they denied the possibility of their existence ; and when he urged them to
look for themselves through his telescope, they refused to have anything to
do with an instrument they despised. An astronomer of Florence gravely
argued that as there were only seven apertures in the head two eyes, two
ears, two nostrils, and one mouth and as there were only seven metals, and
seven days in the week, so there could be only seven planets. As there were
six principal planets and one moon then known, the number was complete,
and Galileo's pretended planets must be impossibilities. But such absurd
arguments could not long obscure the light of truth.

937. THE SUN (0). The Sun, the great source of light
and heat to the planets, is the centre of the solar system. It
is an immense globe, five hundred times as large as all its plan-
ets put together. Its diameter is 882,000 miles. Placed where
the earth is, it would fill the whole orbit of the moon, and
extend 200,000 miles beyond it in all directions. Its volume
is nearly a million and a half times as great as the earth's,
and it contains more than 350,000 times as much matter.

938. Solar Spots. Viewed through a telescope, the sun
looks like a globe of fire. Its surface, however, is not al-
ways wholly luminous. A number of dark spots, surround-
ed by a lighter shadow, are at times scattered here and
there within a zone extending 35 degrees on each side of
the solar equator. The number and size of these spots
differ at different times ; for, while some last a couple of
months or even longer, others change their form from day
to day. They have been known to vanish almost instantly
and to appear as suddenly. Some years none at ah 1 are
visible ; in others, as many as 200 are seen at once, cover-

the work of Copernicus relating to this subject published ? By whom was the truth of
the Copernican system established ? What were the arguments with which Galileo
was met? 93T. What is the Sun ? How great is its diameter ? Placed where the earth
is, how far would it extend ? How does its volume compare with the earth's ? Its
matter ? 938. How docs the sun look, when viewed through a telescope ? Describe
the spots which are sometimes visible. What is said of their number and size ? What



372 ASTRONOMY.

ing so much of the surface as materially to diminish the
quantity of light emitted.

By comparing a number of observations on the solar spots, we find that
they are subject to periodical increase and decrease. They become larger
and more numerous for a certain time till they reach a maximum, after which
they gradually diminish, till all disappear, or nearly so ; new ones then be-
come risible, and go on increasing during the same period as before. This
period seems to be a little over eleven years.

Spots have occasionally appeared of such size that they could be readily
discerned with the nakeji eye. One thus seen for a week in June, 1843, must
have been 77,000 miles across, or nearly ten times the size of the earth.

Astronomers have tried to account for the solar spots in various ways.
The prevailing opinion is that the light received from the sun does not come
from its surface, but from a luminous atmosphere of great depth with which
it is surrounded; and that the spots in question are simply portions of the
dark body of the sun, which become visible when the luminous atmosphere
is opened by upward currents from the surface or any other agency. The
disturbance of this atmosphere, by whatever it is caused, is most frequent
near the solar equator. Peculiarly bright streaks of light, called faculw, are
often found near the spots or where they have just disappeared. They are
supposed to be the ridges of vast waves in the luminous atmosphere just de-
scribed.

939. Constitution of the Sun. The sun's density is
about one-fourth that of the earth. Respecting its consti-
tution little is known, nor are we any better informed as to
what produces its intense heat and light. It was formerly
supposed that the whole mass was in a state of combustion.
But how can such combustion be kept up without dimin-
ishing the material on which it feeds ? The difficulty of
answering this question has led the later astronomers to
point to friction or electricity as the most probable source
of solar heat and light.

940. Motions. The more permanent of the sun's spots,
if observed from time to time, are found to change their
position on its disk, or face. First becoming visible on the

is found "by comparing a number of observations on the solar spots ? What is the
length of the period? Of what size have spots occasionally appeared ? What Avas
the diameter of one seen in June,. 1843? What is the prevailing opinion of astrono-
mers respecting these spots ? What are faeula? What are they supposed to be ?
939. How does the sun's density compare- with the earth's ? What is known respect-
ing its constitution and heat? To what have the later astronomers pointed as the
most probable source of solar heat and light? 940. How is it proved that the sun



THE ZODIACAL LIGHT. 373

east side, they gradually move towards the "west, and in
about thirteen days are lost from sight in that direction.
After a similar period they reappear in the east. This
phenomenon shows that the sun turns on its axis from
west to east ; its revolution is performed in about 25 days,
8 hours.

Besides turning on its axis, the sun, attended by its
planets, moves at the rate of 8 miles a second in a circular
path round a centre far off in the fields of space. So vast
is this path that it will take the sun 18,200,000 years to get
once completely round it.

941. The Zodiacal Light. A faint light, shaped like a
sugar-loaf, is sometimes seen stretching obliquely upward
in the heavens, from 70 to 100 degrees, from that part of
the horizon where the sun is about rising or has just set.
This phenomenon is known as the Zo-di'-a-cal Light. It is
brightest and most distinctly defined in tropical regions,
where it is visible most of the time. In high latitudes it is
seldom clearly seen, except during March and April just
after sun-set, and in September and October immediately
before dawn.

The cause of the zodiacal light is unknown. Some suppose it to be an
expansion of the solar atmosphere ; others, a thin vapor, charged with mat-
ter from the tails of comets, of which the sun's attraction has deprived them ;
others, again, have suggested that it is a remnant of the original matter of
which both sun and planets were made. The latest theory is, that it is a neb-
ulous ring, surrounding the Earth, like the ring of the planet Saturn.

Ttie Planets.

942. By the Planets of the solar system are meant those
heavenly bodies that revolve directly about the sun in ob-
long curves, and shine by its reflected light.

The word planetes in Greek means " a wanderer", and the bodies in ques-
tion are so called in contradistinction to the fixed stars, which keep the same

turns on its axis? What is the time of its revolution ? What other motion has ther
sun ? How largo is the path it travels ? 941. Describe the Zodiacal Light. Where
is it brightest ? When is it seen in high latitudes ? What opinions have been ad-
vanced to account for the zodiacal light? 942. What are the Planets ? What does
the word planetes mean ? From what are the planets to be distinguished ? How



374 ASTEONOMT.

position in the heavens relatively to each other. The planets and the fixed
stars are easily distinguished ; the former shine with a steady light, the latter
twinkle.

943. The moons are sometimes called Secondary Plan-
ets. In that case, the bodies that revolve directly about
the sun are called Primary Planets.

944. The planets are also distinguished as Inferior and
Superior. The Inferior Planets are those that are nearer
to the sun than the earth is ; the Superior Planets are those
that are farther from the sun than the earth is.

945. OKBITS OF THE PLACETS. The path of a planet
round the sun is called its Orbit. The planets being at
different distances from the sun, their orbits differ in length,
.though they are similar in shape.

946. The planetary orbits are not circles, but oblong
curves called Ellipses. Hence a planet is nearer the sun in
one part of its course than in another. That point of its
orbit at which it is nearest the sun is called its perihelion
(plural, perihelia) ; that in which it is farthest from the sun
is its aphelion (plural, aphelid). When a planet's distance

from the sun is spoken of, its mean dis-
tance is meant. This is obtained by add-
ing its greatest and least distance to-
gether and dividing by 2.

These definitions are illustrated in Fig. 330.
ABP C represents an ellipse. S is the sun, situ-
ated not at the centre of the ellipse, but at one of two
points within it called foci. P shows the position
of a planet at its perihelion, and A at its aphelion.

The orbits of the planets lie in different planes,
more or less inclined to each other.

947. Besides their revolution round the sun, the planets
have another motion round their own axes. The time that



can the planets and the fixed stars be told apart? 943. What constitutes the differ-
ence between Primary and Secondary Planets ? 944 Between Inferior and Superior
Planets? 945. What is a planet's orbit? 946. What is the shape of the planetary
orbits ? What is a planet's Perihelion ? Aphelion ? When a planet's distance from
the sun is spoken of, what is meant ? How is the mean distance obtained ? Illus-
trate these definitions with Fig. 330. What is said of the planes of the orbits?
9i7. What other motion have the planets besides their revolution round the sun?




THE PLANETS.



375



it ^akes a planet to make one revolution on its axis is called
its Day.

948. TABLE. A Table of the planets follows, in the or-
der of their distances from the sun, which are given in the
second column. Their diameters in miles are given in the
third column ; the number of our days that it takes them
to revolve round the sun, in the fourth ; and the hours re-
quired for the revolution of each on its axis, in the fifth.
The Tables in the Fifth Edition of Herschel's " Outlines of
Astronomy" (1858) are here followed.



Name.


Distance from
Sun in miles.


Diameter
in miles.


Year expressed in
the Earth's days.


Day expressed
in hours, &c.


Mercury .


36,890,000


3,183


88


21* '5 m


Venus . .


68,770,000


8,103


225


23 21


Earth . .


95,298,260


7,926


3651/4


24


Mars . .


145,205,000


4,546


687


24 37


ASTEROIDS


j from 210 to


est. at from


from 1,191 )


unknown


(62)


1 301 millions


100 to 1,000


to 2,051 )




Jupiter


495,815,500


90,734


4,333


gh 5 5 m 27-


Saturn . .


909,029,700


76,791


10,759


10 29 17


Uranus


1,828,048,000


35,307


30,687


9 30


Neptune .


2,862,404,000


39,793


60,126


unknown



949. Mercury, Venus, Mars, Jupiter, and Saturn, being visible to the
naked eye, were known to the ancients. Uranus was discovered in 1781 by
Sir William Herschel, from whom it was first commonly called Herschel. Its
discoverer gave it the name of Georgium Sidus, in honor of King George III.
Both these names, however, were discarded for the mythological one by
which it is at present known. The first of the asteroids, Ceres, was discov-
ered in 1801 by the Sicilian astronomer Piazzi [pe-at'-ze], Pallas was added
to the list in 1804 ; Juno, in 1804 ; Vesta, in 1807 ; and the remainder, since
1844.

Neptune was discovered in 1846 by Dr. Galle [gal'-la], of Berlin. It was
first called Le Verrier [luTi va-re-a'], in honor of an eminent French astrono-



What is meant by a planet's day ? 948. Eeferring to the Table, which of the planets
do you find the smallest (the asteroids excepted), and which the largest? Which
takes the shortest time to revolve around the sun, and which the longest ? Which
three have a day very nearly as long as the Earth's ? Which three have days less than
half as long as the Earth's? 949. Which of tho planets were known to the ancients?
Which was the next discovered ? What other names has Uranus borne ? When and
by whom was the first asteroid discovered ? When were the rest added to tho list?
When and by whom was Neptune discovered? What was it first called, and why?



376 ASTRONOMY.

mer, who by a series of calculations established the fact that there was a
more distant planet than Uranus, and instructed Dr. Galle in what part of the
heavens to look for it.

950. BODE'S LAW. By comparing the distances of the
planets from the sun, Bode [bo'-da] arrived at the following
law : Take the geometrical progression

3 6 12 24 48 96 192 384,
each term of which (after the second) is obtained by doub-
ling the preceding one. To each term add 4, and we get

4 7 10 16 28 52 100 196 388.
The distances of the nearer planets are approximately pro-
portioned to these numbers. That is, Mercury's distance be-
ing 36,890,000 miles, Venus's will be \ as much, the Earth's
y ; &G. Bode's law, however, does not apply to Saturn,
TJranus, and Neptune. They are all, particularly the last,
much nearer the sun than this law would make them.

951. Fig. 331 shows the comparative size of the planets.
The asteroids are too small to appear on this scale.

Fig. 331.




Herschel uses the following illustration to give an idea of the relative sizo
of the planets and their orbits : " Choose any well levelled field or bowling-
green. On it place a globe two feet in diameter ; this will represent the Sun
Mercury will be represented by a grain of mustard-seed, on the circumference
of a circle 164 feet in diameter for its orbit ; Venus a pea, on a circle of 284
feet in diameter ; the Earth also a pea, on a circle of 430 feet ; Mars a rather
large pin's head, on a circle of G54 feet; the Asteroids, grains of sand, in



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 36 of 42)