The nineteenth century may be called the Age of the Asteroids. It was
on _the first night_ of this century that the first asteroid was
discovered! Through all the former ages, no man on the earth had had
definite knowledge of the existence of such a body. It was reserved
for Guiseppe Piazzi, an Italian astronomer at Palermo, to make known
by actual observation the first member of the planetoid group. If
human history had the slightest regard for the calendars of
mankind--if the eternal verities depended in any measure on the
almanac or the division of time into this age or that--we might look
with wonder on the remarkable coincidence which made the discovery of
the first asteroid to happen in the first evening twilight of the
first day of the nineteenth century!
At the close of the eighteenth century, mankind were acquainted with
all the major planets except Neptune. Uranus, the last of the group,
was discovered by the Elder Herschel, on the night of the thirteenth
of March, 1781. True, this planet had been seen on twenty different
occasions, by other observers; but its character had not been
revealed. Sir William called his new world Georgium Sidus, that is,
the George Star, in honor of the King of England. The world, however,
had too much intelligence to allow the transfer of the name of George
III. from earth to heaven. Such nomenclature would have been unpopular
in America! The name of the king was happily destined to remain a part
of terrestrial history!
For a while it was insisted by astronomers and the world at large that
the new globe, then supposed to bound the solar system on its outer
circumference, should be called Herschel, in honor of its discoverer.
But the old system of naming the planets after the deities of
classical and pagan mythology prevailed; and to the names of Mercury,
Venus, Mars, Jupiter, Saturn, was now added the name Uranus, that is,
in the language of the Greeks, _Heaven_.
Piazzi, scanning the zodiac from his observatory in Palermo, in the
early hours of that first night of the century, noticed a hitherto
unobserved star, which under higher power proved to be a planet. It
presented a small irregular disc, and a few additional observations
showed that it was progressing in the usual manner from west to east.
For some time such a revelation had been expected; but the result did
not answer to expectation in one particular; for the new body seemed
to be too insignificant to be called a world. It appeared rather to be
a great planetary boulder, as if our Mount Shasta had been wrenched
from the earth and flung into space. Investigation showed that the new
body was more than a hundred miles in diameter; but this, according to
planetary estimation, is only the measurement of a clod.
There had been, as we say, expectation of a discovery in the region
where the first asteroid was found. Kepler had declared his belief
that in this region of space a new world might be discovered.
Following this suggestion, the German astronomer Olbers, of Bremen,
had formed an association of twenty-four observers in different parts
of Europe, who should divide among themselves the zodiacal band, and
begin a system of independent scrutiny, either to verify or disprove
Kepler's hypothesis.
There was another reason also of no small influence tending to the
same end. Johann Elert Bode, another German astronomer, born in 1747
and living to 1826, had propounded a mathematical formula known as
Bode's Law, which led those who accepted it to the belief that a
planet would be found in what is now known as the asteroidal space.
Bode's Law, so-called, seems to be no real law of planetary
distribution; and yet the coincidences which are found under the
application of the law are such as to arouse our interest if not to
produce a conviction of the truth of the principle involved. Here,
then, is the mathematical formula, which is known as Bode's Law:
Write from left to right a row of 4's and under these, beginning with
the second 4, place a geometrical series beginning with 3 and
increasing by the ratio of 2; add the two columns together, and we
have a series running 4, 7, 10, etc.; and this row of results has an
astonishing coincidence, or approximate coincidence with the relative
distances of the planets from the sun--thus:
4 4 4 4 4 4 4 4 4
3 6 12 24 48 96 192 384
-- -- -- -- -- -- --- --- ---
4 7 10 16 28 52 100 196 388
The near agreement of this row of results with the row containing the
_actual_ relative distances of the planets from the sun may well
astonish, not only the astronomer, but the common reader. Those
distances--making 10 to represent the distance of the earth--are as
follows:
Mercury, 3.9; Venus, 7.2; Earth, 10; Mars, 15.2; Asteroids, 27.4;
Jupiter, 52; Saturn, 95.4; Uranus, 192; Neptune, 300.
In addition to Kepler's prediction and the indications of Bode's Law,
there was a _general_ reason for thinking that a planetary body of
some kind should occupy the space between the orbits of Mars and
Jupiter. The mean distance of Mars from the sun is about 141,500,000
miles; that of Jupiter, is about 483,000,000 miles. The distance from
one orbit to the other is therefore about 341,500,000 miles. Conceive
of an infinite sheet of tin. Mark thereon a centre for the sun.
Measure out a hundred and forty millions of miles, and with that
radius strike a circle. From the same centre measure out four hundred
and eighty-three millions of miles, and with that radius strike a
circle. Cut out the sheet between the two circles, and the vast space
left void will indicate the vacant area in the mighty disc of our
solar system. That this space should be occupied with _something_
accords with the plan of nature and the skill of the Builder.
So Olbers and his twenty-three associates began, in the last decade of
the eighteenth century, to search diligently for the verification of
Kepler's prediction and the fulfillment of Bode's Law. Oddly enough,
Piazzi was not one of the twenty-four astronomers who had agreed to
find the new world. He was exploring the heavens on his own account,
and in doing so, he found what the others had failed to find, that is,
the first asteroid.
The body discovered answered so little to the hopes of the
astronomical fraternity that they immediately said within themselves:
"This is not he; we seek another." So they continued the search, and
in a little more than a year Olbers himself was rewarded with the
discovery of the second of the planetoid group. On the twenty-eighth
of March, 1802, he made his discovery from an upper chamber of his
dwelling in Bremen, where he had his telescope. On the night in
question he was scanning the northern part of the constellation of
Virgo, when the sought-for object was found. This body, like the first
of its kind, was very small, and was found to be moving from west to
east in nearly the same orbit as its predecessor.
Here then was something wonderful. Olbers at once advanced the
hypothesis that probably the two bodies thus discovered were fragments
of what had been a large planet moving in its orbit through this part
of the heavens. If so there might be--and probably were--others of
like kind. The search was at once renewed, and on the night of the
first of September, 1804, the third of the asteroid group was found by
the astronomer Hardy, of Bremen. The belief that a large planet had
been disrupted in this region was strengthened, and astronomers
continued their exploration; but two years and a half elapsed before
another asteroid was found. On the evening of March 29, 1807, the
diligence of Olbers was rewarded with the discovery of the fourth of
the group, which like its predecessors, was so small and irregular in
character as still further to favor the fragmentary theory.
How shall we name the asteroids? Piazzi fell back upon pagan mythology
for the name of his little world, and called it Ceres, from the Roman
goddess of corn. Olbers named the second asteroid Pallas; the third
was called Juno--whose rank in the Greek and Roman pantheon might have
suggested one of the major planets as her representative in the skies;
and the fourth was called Vesta, from the Roman divinity of the
hearthstone.
Here then there was a pause. Though the zodiac continued to be swept
by many observers, a period of more than thirty-eight years went by
before the fifth asteroid was found. The cycle of these discoveries
strikingly illustrates the general movement of scientific progress.
First there is a new departure; then a lull, and then a resumption of
exploration and a finding more fertile than ever. It was on the night
of the eighth of December, 1845, that the German astronomer Hencke
discovered the fifth asteroid and named it Astræa. After a year and a
half, namely, on the night of the first of July, 1847, the same
observer discovered the sixth member of the group, and to this was
given the name Hebe. On the thirteenth of August in the same year the
astronomer Hind found the seventh asteroid, and named it Iris. On the
eighteenth of October following he found the eighth, and this was
called Flora. Then on the twenty-fifth of April, 1848, came the
discovery of Metis, by Graham. Nearly a year later the Italian De
Gasparis found the tenth member of the system, that is, Hygeia. De
Gasparis soon discovered the eleventh body, which was called
Parthenope. This was on the eleventh of May, 1850.
Two other asteroids were found in this year; and two in 1851. In the
following year _nine_ were discovered; and so on from year to year
down to the present date. Some years have been fruitful in such finds,
while others have been comparatively barren. In a number of the years,
only a single asteroid has been added to the list; but in others whole
groups have been found. Thus in 1861 twelve were discovered; in 1868,
twelve; in 1875, _seventeen_; in 1890, fourteen. Not a single year
since 1846 has passed without the addition of at least one known
asteroid to the list.
But while the number has thus increased to an aggregate at the close
of 1890 of three hundred and one, many of the tiny wanderers have
escaped. Some have been rediscovered; and it is possible that some
have been twice or even three times found and named. The whole family
perhaps numbers not only hundreds, but thousands; and it can hardly be
doubted that only the more conspicuous members of the group have ever
yet been seen by mortal eye.
A considerable space about the centre of the planetary zone between
Mars and Jupiter is occupied with these multitudinous pigmy worlds
that follow the one the other in endless flight around the sun. It is
a sort of planetary shower; and it can hardly be doubted that the
bodies constituting the flight are graded down in size from larger to
smaller and still smaller until the fragments are mere blocks and bits
of world-dust floating in space. Possibly there may be enough of such
matter to constitute a sort of planetary band that may illumine a
little (as seen from a distance) the zone where it circulates.
As to the origin of this seemingly fragmentary matter, we know
nothing, and conjectures are of little use in scientific exposition.
It may be true that a large planet once occupied the asteroidal space,
and that the same has been rent by some violence into thousands of
fragments. It may be observed that the period of rotation of the
inferior planets corresponds in general with that of our earth, while
the corresponding period of the superior or outside planets is less
than one-half as great. The forces which produced this difference in
the period of rotation may have contended for the mastery in that part
of our solar system where the asteroids are found; and the disruption
may have resulted from such conflict of forces.
Or again, it may be that a large planet is now in process of formation
in the asteroidal space. Possibly one of the greater fragments may
gain in mass by attracting to itself the nearer fragments, and thus
continue to wax until it shall have swept clean the whole pathway of
the planetary matter, except such small fragments as may after æons of
time continue to fall upon the master body, as our meteorites now at
intervals rush into our atmosphere and sometimes reach the earth.
Some astronomers have given and are still giving their almost
undivided attention to asteroidal investigation. The discoveries have
been mostly made by a few principal explorers. The astronomer, Palisa,
from the observatory of Pola and that of Vienna, has found no fewer
than seventy-five of the whole group. The observer, Peters, at
Clinton, New York, has found forty-eight asteroids; Luther, of
Düsseldorf, twenty-four; Watson, of Ann Arbor, twenty-two; Borrelly,
of Marseilles, fifteen; Goldschmidt, of Paris, fourteen, and Charlois,
of Nice, fourteen. The English astronomers have found only a few.
Among such, Hind of London, who has-discovered ten asteroids, is the
leader.
The Italian, German and American astronomers are first in the interest
and success which they have shown in this branch of sky-lore. Their
investigations have made us acquainted with the dim group of little
worlds performing their unknown part in the vast space between the
Warrior planet and Jove.