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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

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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 32 of 38)
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in the moon's south limb will see the earth to the northward ,
those in the north limb will see it to the southward; those in
the east limb will see it to the westward ; while those in the
west limb will see it to the eastward ; and all will see it nearer
the horizon in proportion to their own distance from the centre
of the moon's disk. Similar appearances are exhibited to the
inhabitants of all secondary planets. These observations are
predicated on the supposition that the moon is inhabited. But
it is not generally believed that our Tnoon is inhabited, or in its
present condition fitted for the residence of any class of beings
1315. It is a singular circumstance, that before the discovery tf



ASTRONOMY. 37l

CTraims some d.sturbances and deviations were observed hy astron.
jniers in the motions of Jupiter and Saturn, which they could
account for onl y on the supposition that these two planets were in
duenced by the attraction of some more remote and undiscovered
planet. The discovery of Uranus completely verified their opinions.
and shows the extreme nicety with which astronomers observe the
motions of planets.



What led to the ^^ ^ F NEPTUNE. The discovery of the
discovery of the planet Neptune (named originally Le Verrier,
planet Neptune ? fi . om itg discovererj in 1846) is one of the g rea test

triumphs which the history of science records. As certain per-
turbations of the movements of Saturn led astronomers to sus-
pect the existence of a remoter planet, which suspicions were
fully confirmed in the discovery of Uranus, so also, after the dis-
covery of Uranus, certain irregularities were perceived in his
motiong, that led the distinguished astronomers of the day to the
belief that even beyond the planet Uranus still another undis-
covered planet existed, to reward the labors of the discoverer.
Accordingly Le Verrier, a young French astronomer, urged by
his friend A tag, determined to devote himself to the attempt
at discovery. With indefatigable industry he prepared new
tables of planetary motions, from which he determined the pertur-
bations of the planets Jupiter, Saturn, and Uranus, and as early
as June, 1846, in a paper presented to the Academy of Sciences
in Paris, he pointed out where the suspected planet would be
on the 1st of January, 1847. He subsequently determined the
mass and the elements of the orbits of the planet, and that, too, be-
fore it had been seen by a human eye. On the 18th of September
of 1846, he wrote to his friend, M. Galle, of Berlin, requesting
him to direct his telescope to a certain point in the heavens, where
he suspected the stranger to be. His friend complied with his
request, and on the first evening of examination discovered a
strange star of the eighth magnitude, which had not been laid down
in any of the maps of that portion of the heavens. The follow-
ing evening it was found to have moved in a direction and with a
velocity very nearly like that which Le Verrier had pointed out
Che planet wa t s found within less than one degree of the place
16



J72 NATUKA.L PHILOSOPHY.

where Le Verrier had located it. It was subsequently ascer-
tained that a young English mathematician, Mr. Adams, of
Cambridge, had been engaged in the same computations, and
had arrived at nearly the same results with Le Verrier.

1317. What shall we say of science, then, that enables its devoted
followers to reach out into space, and feel successfully in the dark
for an object more than twenty-eight hundred millions of iniJes
distant ?

1318. In conclusion of this brief notice of the planets, a plate
is here presented showing the relative appearance of the planets
is viewed through a telescope. It will be observed that the
planets Mercury and Venus have similar phases to those of our
uioon.

Pig 190




Relative Telescopic appearance of the Planets.



, 5 a 1319. OF COMETS. The word Comet is de-
? rived from a Greek word, which means hair; and
this name is given to a numerous class of bodies, which occa-
sionally visit and appear to belong to the solar system. These
bodies seem to consist of a nucleus, attended with a lucid
haze, sometimes resembling flowing hair ; from whence the
aame is derived. Some comets appear to consist wholly



ASTKONOMY. 373

af tftis hazy or hairy appearance, which is frequently ealloci
the tail of the comet.

Fig. 191




Comet of 1811, one of the most brilliaut of modern times. Period, 2888

years.

1320. In ancient times the appearance of comets was regard-
ed with superstitious fear, in the belief that they were the fore-
runners of some direful calamity. These fears have now been
banished, and the comet is viewed as a constituent member of
the system, governed by the same harmonious and unchanging
laws which regulate and control a the other heavenly bodies.

1321. The number of comets that have occasionally appeared
within the limits of the solar system is variously stated from 350
to 500. The paths or orbits of about 98 of these have been
calculated from observation of the times at which they most
nearly approached the sun ; their distance from it and from the
earth at those times ; the direction of their movements, whether
from cae-t to wet?t, or from we?t to east ; and the places in tli3



374 NATURAL P11ILOSOPII1.

starry sphere at which their orbits crossed that of the earth and
their inclination to it. The result is, that, of these 98, 24 passed
between the sun and Mercury. 33 passed between Mercury and
Venus, 21 between Venus and the Earth, 16 between the Earth
and Mars, 3 between Mars and Ceres, and 1 between Ceres and
Japiter : that 50 of these comets moved from east to west ; that
fcheir orbits were inclined at every possible angle to that of the
earth. The greater part of them ascended above the orbit of
the earth when very near the sun ; and some were observed to
dash down from the upper regions of space, and, after turning
round the sun, to mount again.

1322. Comets, in their revolution, describe
What is the shape
of the orbits of long narrow ovals. They approach very near

comets ? the sun in one of the ends of these ovals, and

when they are in the opposite end of the orbit their distance
from the sun is immensely great.

1323. The extreme nearness of approach to the sun gives to
a. comet, when in perihelion, a swiftness of motion prodigiously
great. Newton calculated the velocity of the comet of 1680 to
be 880,000 miles an hour. This comet was remarkable for its
near approach to the sun, being no further than 580,000 miles
from it, which is but little more than half the sun's diameter
Brydone calculated that the velocity of a comet which he ob-
served at Palermo, in 1V70, was at the rate of two millions and
a half of miles in an hour.

1324. The luminous stream, or tail, of a comet, follows it aa
it approaches the sun, and goes before it when the 3omet recedes
from tho sun. Newton, and some other astronomers, considereo
the tails of comets to be vapors, produced by the excessive heat
of the sun. Others have supposed them to be caused by a re-
pulsive influence of the sun. Of whatever substance they may
be, it is certain that it is very rare, because the stars may bo
distinctly seen through it.

1325 The tails of comets differ very greatly in length,



&8T1CONOM1'.



and some are attended apparently by only a small cloudy
light, while the length of the tail of othsrs has been esti-
mated at from 50 to 80 millions of miles.



Kg. 192




The comet of 1680, observed by Newton. Eapidity of its motion around
the sun, a million of miles in an hour.

Length of tail, 100 millions of miles. Period, 600 years. It has never re-
appeared.

1326. It has been argued that comets consist of very little
solid substance, because, although they sometimes approach very
near to the other heavenly bodies, they appear to exert no sensi-
ble attractive force upon those bodies. It is said that in 1454
the moon was eclipsed by a comet. The comet must, therefore,
have been very near the earth (less than 240,000 miles) ; yet it
produced no sensible effect on the earth or the moon ; for it did
aoi cause them to make any perceptible deviation from their



37<3 NATURAL PHILOSOPHY.

accustomed paths round the sun. It has been ascertained tlt&i
comets are disturbed by the gravitating power of the planets ;
but it does not appear that the planets are in like manner affected
by comets.

Some comets have exhibited the appearance of two or raoiv
tails, and the great comet of 1744 had six

Fig 193




The great comet of 1744.



ASTRONOMY.



377



J8 4 27. Many comets escape observation because tb-.y traverse
fhat part of the heavens only which is above the borizon in the
Jay-time. They are. therefore, lost in the brilliancy of the sun.
and can be seen only when a total eclipse of the sun takes place.
Seneca, 60 years before the Christian Era, states that a large
comet was actually observed very near the sim, during an eclipse

1328. Dr. Halley, Professor Encke and Gambart, are the first
astronomers that ever successfully predicted the return of a
comet. The periodical time of Halley's comet is about 76 years.
It appealed last in the fall of 1835, and presented diilererit aj>




Halley's comet, as seen by (Sir Joiiu iierscheJ, October 29th, 1835. Da-
changeable in its appearance. First recognized by Halley in 1682. Period,
16 years.



378



^"ATUKAL PHILOSOPHY.



pearances from (113*61601 points of observation. That of Enck
is about 1200 days ; tliat of Biela, about 6 years. This last
comet appeared in 1832 and in 1838.

Pig. 195.




Halley's comet, as seen by Struve, Oct. 12th, 1835.
in 1682. Period, 75 years.



First seen by Halley



1329. The comet of 1758, the return of which was predicted
oy Dr. Halley, was regarded with great interest by astronomers,
because its return was predicted. But four revolutions before,
in 1456, it was looked upon with the utmost horror. Its long
tail spread consternation over all Europe, already terrified by
the rapid success of the Turkish arms. Pope Callixtus, on this
occasion, ordered a prayer, in which both the comet and the
Turks were included in one anathema. Scarcely a year or a



ASTRONOMY. 37 y

month now elapses without the appearance of a comet in our
system. But it is now known that they are bodies of such ex-
treme rarity that our clouds are massive in comparison with
them. They have no more density than the air under an ex-
nausted receiver. Herschel saw stars of the 6th magnitude
through a thickness of 30,000 miles of cometic matter. The
number of comets in existence within the compass of the solai
system is stated by some astronomers as over seven millions.

1330. Fig. 194 represents Halley's comet, as seen by Sir John
Herschel, while Fig. 195 represents the. same comet as seen only
a few days before by Struve.

1331. THE COMET or 1856. ^ The following interesting details in
relation to a comet expected in 1856 were given by Babinet, an em-
inent French astronomer. It is translated from the Courier des
Etats Unis.

" This comet is one of the grandest of which historians make
mention. Its period of revolution ia about three hundred years. It
was seen in the years 104, 392, 683, 975, 1264, and the last time in
1556. Astronomers agreed in predicting its return in 1848 ; but it
failed to appear, and continues to shine still unseen by us. Already
the observatories began to be alarmed for the fate of their beautiful
wandering star, when a learned calculator of Middlebourg, M.
Bomrne, reassured the astronomical world of the continued existence
of the venerable and magnificent comet.

" Disquieted, as all other astronomers were, by the non-arrival
of the comet at the expected time, M. Bomme, aided by the prepar-
atory labors of Mr. Hind, has revised all the calculations and esti-
mated all the actions of all the planets upon the comet for three
hundred years of revolution. The result of this patient labor gives
the arrival of the comet in August, 1858, with an uncertainty of
two years, more or less ; so that from 1856 to 1860 we may expect
the great comet which was the cause of the abdication of the Em-
peror Charles V., in 1556.

" It is known that, partaking of the general superstition, which
interpreted the appearance of a comet as the forerunner of som**
fatal event, Charles V. believed that this comet addressed its menaces
particularly to him, as holding the first rank among sovereigns. The
great and once wise but now wearied and shattered monarch, had
been for some time the victim of cruel reverses. There were threat-
ening indications in the political, if not in the physical horizon, of a
still greater tempest to come. lie was left to cry in despair, ( For-
tune abandons old men.' The appearance of the blazing star seemed
Co him an admonition from Heaven that he must cease to bo a sov-
if he would avoid a fatality from which one without author-

16*



380 NATURAL PHILOSOPHY.

ity might be spared. It is known that the emperor survived his
abdication but a little more than two years.

'* Another comet, which passed near us in 1835, and which has
appeared 25 times since the year 13 before the Christian Era, hari
been associated by the (superstitious with many important events
which have occurred near the periods of its visitation.

" In 1066, William the Conqueror landed in England at the head
of a numerous army about the time that the comet appeared which
now bears the name of Halley's comet. The circumstance was
regarded by the English as a prognostic of the victory of the Nor-
mans. It infused universal terror into the rninds of the people, and
contributed not a little towards the submission of the country after
the battle of Hastings, as it had served to discourage the soldiers
of Harold before the combat. The comet is represented upon the
famous tapestry of Bayeux, executed by Queen Matilda, the wife of
the conqueror.

" This celebrated tapestry is preserved in the ancient episcopal
palace at Bayeux. It represents the principal incidents, including
the appearance of the comet, in the history of the conquest of Eng-
land by William, Duke of Normandy. It is supposed to have been
executed by Matilda, the conqueror's wife, or by the Empress Ma-
tilda, daughter of Henry I. It consists of a linen web, 214 feet in
length and 20 inches broad ; and is divided into 72 compartments,
each having an inscription indicating its subject. The figures ara
all executed by the needle.

" The same comet, in 1451, threw terror among the Turks under
the command of Mahomet II., and into the ranks of the Christians
during the terrible battle of Belgrade, in which forty thousand Mus-
sulmans perished. The comet is described by historians of the time
as ' immense, terrible, of enormous length, carrying in its train a
tail which covered two celestial signs (60 degrees), and producing
universal terror.' Judging from this portrait, comets have singu-
larly degenerated in our day. It will be remembered, however, that
in 1811 there appeared a comet of great brilliancy, which inspired
some superstitious fears. Since that epoch science has noted nearly
30 comets, which, with few exceptions, were visible only by the aid
of the telescope. Kepler, when asked how many comets he thought
there were in the heavens, answered, ' As many as there are fish in
the sea.'

" Thanks to the progress of astronomical science, these singular
8tars are no longer objects of terror. The theories of Newton,
Halley, and their successors, have completely destroyed the imag-
inary empire of comets. As respects their physical nature, it was
for a long time believed that they were composed of a compact
centre, surrounded by a luminous atmosphere. On this subject the
opinion of M. Babinet, who must be regarded as good authority on
such questions, is as follows : ' Comets cannot exercise any materiaJ
influence upon our globe ; and the earth, should it traverse a comet
in its entire breadth, w< uld perceive it no more than if it should jrosw



a cloud A hundred thousand millions of tmis lighter than our at-
mosphere, and which could no more make its way through our air
than the slightest puff of an ordinary bellows could make its way
through an anvil.' It would be difficult to find a comparison more
reassuring. ' ' *

What are the 1332 ' F TIIE FlXED S ' rARS ' ~ The Fixed
Fixed Stars Stars are all supposed to be immensely large
suppose*/ to be? bodieg; like our Qwn ^ shining by their

c.wn liglit, which they dispense to systems of their own

, 1383. They are classed by their apparent

fixed stars magnitudes, those of the sixth magnitude being
classified? the smallest tnat can be geeu by the naked

eye. Stars which can be seen only by means of the telescope

* THE COMET OP 1853. Mr. Hind, in a letter to the Dmdon Times, give?
the following particulars with regard to the comet which appeared during
the year now closing (1853):

" The comet which has been so conspicuous during the last week was very
favorably seen here on Saturday, and again on Sunday evening. On the
latter occasion, allowing for the proximity of the comet to the horizon, and
the strong glow of twilight, its nucleus was fully as bright as an average
star of the first magnitude ; the tail extended about three degrees from the
bead. When viewed in the comet-seeker, the nucleus appeared of a bright
gold color, and about half the diameter of the planet Jupiter, which was
shining at the same time in the southern heavens, and cou'd be readily com-
pared with the comet. The tail proceeds directly from the head in a single
stream, an] not, as sometimes remarked, in two branches. The distance of
this body irom the earth at 8 o'clock last evening, was 80,000,000 miles ;
and hence it results, that the actual diameter of the bright nucleus was
8000 miles, or about equal to that of the earth, while the tail had a real
'ength of 4,500,000 miles, and a breadth of 250,000, which is rather over the
distance separating the moon from the earth. It is usual to assume that
the intensity of a comet's light varies as the reciprocal of the products of
the squares of the distance from the earth and sun; but the present one has
undergone a far more rapid increase of brilliancy than would result from
this hypothesis. The augmentation of light will go on till the 3rd of Sep-
tember, and it will be worth while to look for the comet in the day-time
about that date ; for this purpose an equatorially mounted telescope will
bo required, and I would suggest the addition of a light green or red glass,
to take off the great glare of sunlight, the instrument being adjusted to a
i'ccus on the planet Venus. This comet was discovered on the 10th of June,
by Mr. Kliukenfues, of the Observatory at Gottingen, but was not bright
enough to be seen without a telescope until about August 13. In a letter,
copied into the Times a few days since, Sir William Hamilton hints at the
possibility of this being the comet I had been expecting; but I avail myself
oi the present opportunity of stating that such is not the case, the elements
of tho orbits having no resemblance. The comet referred to will probably
reappeir between the years 1858 and 1861 ; and, if the perihelion passage
takes place during the summer months, we may expect to see a body of tkr
u\-re imposing aspect than the one at present visible."



,W2 NATURAL PHU

are caLed telescopic stars. Th >y, also, are classified;

the classes reaching even to the seventeenth or twentieth

magnitude.

How many 1334. The number of the stars of the

stars are there first magnitude is about twenty-four : of
of the first and ., ", . , . ~ A v, -, . ,

second magni- th e second magnitude, fifty ; of the third.

tude f two hundred. The number of the smallest,

visible without a telescope, is from twelve to fifteen
thousand.

How many of 1335. Within a few years the distances
the fixed stars of nine of the fixed stars have been calcu-
have had their lated> rpj^ distance is so immense, that
distances very .11.

nearly ascer- light, travelling with the inconceivable
tainedf velocity of nearly two hundred thousand

miles in a second of time, from Sirius, is more than
twenty years in reaching the earth ; from Arcturus,
more than twenty-five years ; and from the Pole Star,
more than forty-eight years.

1336. Tens of thousands of years must roll away before
the most swiftly-flying of all the fixed stars can complete
even a small fragment of its mighty orbit ; but such has
been the advance of science, that if a star move so slowly
'as to require five millions of years to complete its revo-
lution, its motion couid be perceived in one year ; and in
ten years its velocity can be computed, and its period wiU
become known in the lifetime of a single observer.

Who first di 1337. The stars are the fixed points k
tided the stars which we must refer in observations of the



niotions of a11 the heavenly bodies. Hence
the stars were grouped in the earliest ages,
(but by whom we know not), numbered and divided into
constellations, the names of which have survived the fal] of
empires.



ASTRONOMY. ^Scl

What probably iS38. It is generally supposed that part,
causes the dif- ^ llot a u of t } ie c iiff ereilce i n the apparent
fcrenceinthe . ' , . . * {_ ...

^parent size magnitudes ol the stars is owing to the dif-

ofthe stars? ference in their distance.

1339. The distance of the stars, according to Sir J.
ilerschel, cannot be less than 19,200,000,000,000 miles.
How much greater it really is, we know not, except in
a few cases.

1340. Although the stars generally appear fixed, they all have
motion ; but their distance being so immensely great, a rapid mo-
tion would not perceptibly change their relative situation in two or
three thousand years. Some have been noticed alternately to ap-
pear and disappear. Several that were mentioned by ancient as-
tronomers are not now to be seen ; and some are now observe* 1 ,
which were unknown to the ancients.

1841. Many stars which appear single to the naked eye, when
viewed through powerful telescopes, appear double, treblo, and evei.
quadruple. Some are subject to variation ir.. their apparent magni-
tude, at one time being of the second or third, and at another of
the fifth or sixth magnitude.

What is the ' 1342. The Galaxy, or Milky Way, is a
Galaxy? remarkably light, broad zone, visible in

the heavens, passing from noith-east to south-west. It
is known to consist of an immense number of stars,
which, from their apparent nearness, cannot be distin-
guished from each other by the naked eye.

1343. Sir Wm. Herschel saw, in the course of a quarter of an
hour, the astonishing number of 116,000 stars pass through the
deld of his telescope, while it was directed to the milky way.

1344. The ancients, in reducing astronomy to a sci-
ence, formed the stars into clusters, or constellations, to
which they gave particular names.

1345. The number of constellations among the ancienta
\vas about 50. The moderns have added about 50 more.

1346. Oar observations of the stars and nebulae are confined
principally to those of the northern hemisphere. Of the

tious near the south yole we know but little.



NATUliAL PHILOSOPHY.

What effect 1847. In determining the true place of any

] a$ h^on r the of the celestial bodies > the refractive power of
length oj tht the atmosphere must always be taken into
**y* consideration. This property of the atmo-

sphere adds to the length of the days, by causing the sun
to appear before it has actually risen, and by detaining its
appearance after it has actually set.

1348. On a celrstial globe, the largest star in each constellation
is usually designated by the first letter of the Greek alphabet, and
the next largest by the second, &c. When the Greek alphabet is
exhausted, the English alphabet, and then numbers, are used.

Wh ar the 1349. The stars, and other heavenly bodies
stars never are never seen in their true situation, because

seen in their ^ motion of light is progressive ; and. during
true position ? . 6

the time that light is coming to the earth,

the earth is constantly in motion. In order, therefore, to
see a star, the telescope must be turned somewhat before
the star, and in the direction in which the earth moves.

Wliat is meant ^ 35 * ^ ence ' a ra y ^ ^8 nt P assin g through
by the aberra- the centre of the telescope to the observer's
Hon of light * e ^ Q ( j oeg not comc i(j e w j t h a direct line from

his eye to the star, but makes an angle with it ; and this is
termed the aberration of light.

What is the 1351. The daily rotation of the earth on its



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 32 of 38)