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Page 34
"The stars and the mail�d moon,
Though they seem to fall and die,
Still sweep in their embattled lines
An endless reach of sky.
"And though the hills of Death
May hide the bright array,
The marshalled brotherhood of souls
Still keeps its onward way.
"Upward, forever upward,
I see their march sublime,
And hear the glorious music
Of the conquerors of Time.
"And long let me remember
That the palest fainting one
May to diviner vision be
A bright and blazing sun."
THOMAS BUCHANAN READ.
[Page 117]
VII.
SHOOTING-STARS, METEORS, AND COMETS.
"The Lord cast down great stones from heaven upon them unto Azekah,
and they died."--_Joshua_ x. II.
[Page 118]
[Illustration: A SWARM OF METEORS MEETING THE EARTH.
Their orbits are all parallel. Those coming in direct line to the
eye appear as stars, having no motion. Those on one side of this
line are seen in foreshortened perspective. Those furthest from
the centre, other things being equal, appear longest. The centre,
called the radiant point, of these November meteors is situated
in Leo; that of the August meteors in Perseus. Over fifty such
radiant points have been discovered. Over 30,000 meteors have been
visible in an hour.]
[Page 119]
VII.
_SHOOTING-STARS, METEORS, AND COMETS._
Before particularly considering the larger aggregations of matter
called planets or worlds as individuals, it is best to investigate
a part of the solar system consisting of smaller collections of
matter scattered everywhere through space. They are of various
densities, from a cloudlet of rarest gas to solid rock; of various
sizes, from a grain's weight to little worlds; of various relations
to each other, from independent individuality to related streams
millions of miles long. When they become visible they are called
shooting-stars, which are evanescent star-points darting through
the upper air, leaving for an instant a brilliant train; meteors,
sudden lights, having a discernible diameter, passing over a large
extent of country, often exploding with violence (Fig. 48), and
throwing down upon the earth aerolites; and comets, vast extents
of ghostly light, that come we know not whence and go we know not
whither. All these forms of matter are governed by the same laws
as the worlds, and are an integral part of the solar system--a
part of the unity of the universe.
[Illustration: Fig. 48.--Explosion of a Bolide.]
Everyone has seen the so-called shooting-stars. They break out
with a sudden brilliancy, shoot a few degrees with quiet speed,
and are gone before we can say, "See there!" The cause of their
appearance, the [Page 120] conversion of force into heat by their
contact with our atmosphere, has been already explained. Other facts
remain to be studied. They are found to appear about seventy-three
miles above the earth, and to disappear about twenty miles nearer
the surface. Their average velocity, thirty-five, sometimes rises to
one hundred miles a second. They exhibit different colors, according
to their different chemical substances, which are consumed. The
number of them to be seen on different nights is exceedingly
variable; sometimes not more [Page 121] than five or six an hour,
and sometimes so many that a man cannot count those appearing in a
small section of sky. This variability is found to be periodic.
There are everywhere in space little meteoric masses of matter, from
the weight of a grain to a ton, and from the density of gas to rock.
The earth meets 7,500,000 little bodies every day--there is
collision--the little meteoroid gives out its lightning sign of
extinction, and, consumed in fervent heat, drops to the earth as gas
or dust. If we add the number light enough to be seen by a
telescope, they cannot be less than 400,000,000 a day. Everywhere we
go, in a space as large as that occupied by the earth and its
atmosphere, there must be at least 13,000 bodies--one in 20,000,000
cubic miles--large enough to make a light visible to the naked eye,
and forty times that number capable of revealing themselves to
telescopic vision. Professor Peirce is about to publish, as the
startling result of his investigations, "that the heat which the
earth receives directly from meteors is the same in amount which it
receives from the sun by radiation, and that the sun receives
five-sixths of its heat from the meteors that fall upon it."
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