Part 7 (1/2)

At the close of the eighteenth century, mankind were acquainted with all the major planets except Neptune. Ura.n.u.s, 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 circ.u.mference, should be called Herschel, in honor of its discoverer.

But the old system of naming the planets after the deities of cla.s.sical and pagan mythology prevailed; and to the names of Mercury, Venus, Mars, Jupiter, Saturn, was now added the name Ura.n.u.s, 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 un.o.bserved 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 s.p.a.ce. 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 s.p.a.ce a new world might be discovered.

Following this suggestion, the German astronomer Olbers, of Bremen, had formed an a.s.sociation 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 s.p.a.ce.

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 astonis.h.i.+ng 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; Ura.n.u.s, 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 s.p.a.ce 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 s.p.a.ce left void will indicate the vacant area in the mighty disc of our solar system. That this s.p.a.ce should be occupied with _something_ accords with the plan of nature and the skill of the Builder.

So Olbers and his twenty-three a.s.sociates 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...o...b..t 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 G.o.ddess 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 ill.u.s.trates 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 Astraea. 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 pa.s.sed 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 s.p.a.ce about the centre of the planetary zone between Mars and Jupiter is occupied with these mult.i.tudinous 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 const.i.tuting 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 s.p.a.ce. Possibly there may be enough of such matter to const.i.tute 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 s.p.a.ce, 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 s.p.a.ce. Possibly one of the greater fragments may gain in ma.s.s 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 aeons 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 princ.i.p.al 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 Dusseldorf, twenty-four; Watson, of Ann Arbor, twenty-two; Borrelly, of Ma.r.s.eilles, 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.