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 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; 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.

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 s.p.a.ce between the Warrior planet and Jove.

THE STORY OF NEPTUNE.

The discovery of the planet Neptune by Dr. Galle on the twenty-third of September, 1846, was one of the most important events in the intellectual history of this century. Certainly it was no small thing to find a new world. Discoverers on the surface of our globe are immortalized by finding new lands in unknown regions. What, therefore, should be the fame of him who finds a new world in the depths of s.p.a.ce? Perhaps the discoverer of an asteroid or planetary moon may not claim, in the present advanced stage of human knowledge, to rank among the flying evangels of history; but he who found the great planet third in rank among the worlds of the solar system, a world having a ma.s.s nearly seventeen times as great as that of our own, may well be regarded as one of the immortals.

We have referred the discovery of Neptune to Dr. Johann Gottfried Galle, the German astronomer and Professor of Natural Sciences at Berlin. But this Dr. Galle was only the _eye_ with which the discovery was made. He was a good eye; but the eye, however clear, is only an organ of something greater than the eye, and that something in this case consisted of two parts. The first part was Urbain Jean Joseph Leverrier, the French astronomer, of the Paris Observatory. The other part was Professor John Couch Adams, the astronomer of the University at Cambridge, England. These two were the thinkers; that is, they were, as it were, jointly the great mind of the age, of which Galle was the eye.

In getting a clear notion of the discovery of Neptune, several other personages are to be considered. One of these is the astronomer Alexis Bouvart, of France, who was born in Haute Savoie, in 1767, and died in June of 1843, three years before Neptune was found. Another personage was his nephew, the astronomer E. Bouvart, and a third was the noted Prussian, Friedrich Wilhelm Bessel, Director of the Observatory at Konigsberg, who was born in 1784, and died on the seventeenth of March, 1846, only six months before the discovery of our outer planet.

Still another character to be commemorated is the English astronomer Professor James Challis, Plumian Professor and Director of the Observatory at Cambridge, England. This contributor to the great event was born in 1803, and died at Cambridge on the third of December, 1882. Still another, not to be disregarded, is Dr. T.J. Hussey, of Hayes, England, whose mind seems to have been one of the first to antic.i.p.ate the existence of an ultra-Uranian planet. And still again, the English astronomer royal, Sir G.B. Airy must be mentioned as a contributor to the final result; but he is to be regarded rather as a contributor by negation. The great actors in the thing done were Leverrier, Adams and Galle. English authors contend strongly for placing the names in this order: Adams, Leverrier and Galle.

Suffice it to say that when Ura.n.u.s was discovered by the elder Herschel in 1781, that world was supposed to be the outside planet of our system. Hitherto the splendid Saturn had marked the uttermost excursion of astronomical knowledge as it respected our solar group.

For about a quarter of a century after Herschel's discovery the world rested upon it as a finality. The orbit of Ura.n.u.s was thought to circ.u.mscribe the whole. But in the meantime, observations of this...o...b..t led to the knowledge that it did not conform in all respects to astronomical and mathematical conditions. The orbit showed irregularities, disturbances, perturbations, that could not be accounted for when all of the known mathematical calculations were applied thereto. Ura.n.u.s was seen to get out of his path. At times he would lag a little, and then at other times appear to be accelerated.

Each year, when the earth would swing around on the Uranian side of the sun, the observations were renewed, but always with the result that the planet did not seem to conform perfectly to the conditions of his...o...b..t. What could be the cause of this seeming disregard of mathematical laws?

Astronomers could not accept the supposition that there was any actual violation of the known conditions of gravitation. Certainly Ura.n.u.s was following his...o...b..t under the centripetal and centrifugal laws in the same manner as the other planets. There must, therefore, be some undiscovered disturbing cause. It had already been noted that in the case of the infra-Uranian planets they were swayed somewhat from their paths by the mutual influence of one upon the other. This was noticeable in particular in the movements of Jupiter, Saturn and Ura.n.u.s. When Saturn, for instance, would be on the same side of the sun with Jupiter, it might be noted that the latter was drawn outward and the former inward from their prescribed curves. The perturbation was greatest when the planets were nearest, together. In like manner Ura.n.u.s did obeisance to both his huge neighbors on the sun's side of his...o...b..t. He, too, veered toward them as he pa.s.sed, and they in turn recognized the courtesy by going out of their orbits as they pa.s.sed.

What, therefore, should be said of the outswinging movement of Ura.n.u.s from his...o...b..t in that part of his course where no disturbing influence was known to exist? Certainly _something_ must be in that quarter of s.p.a.ce to occasion the perturbation. What was it?

It would appear that the elder Bouvart, the French astronomer referred to above, was the first to suggest that the disturbances in the orbit of Ura.n.u.s, throwing that planet from his pathway outward, might be and probably were to be explained by the presence in outer s.p.a.ce of an unknown ultra-Uranian planet. Bouvart prepared tables to show the perturbations in question, and declared his opinion that they were caused by an unknown planet beyond. No observer, however, undertook to verify this suggestion or to disprove it. Nor did Bouvart go so far as to indicate the particular part of the heavens which should be explored in order to find the undiscovered world. His tables, however, do show from the perturbations of the orbits of Jupiter, Saturn and Ura.n.u.s that the same are caused by the mutual influence of the planets upon one another.

It seems to have remained for Dr. T.J. Hussey, of Hayes, England, to suggest the actual discovery of the unknown planet by following the clew of the disturbance produced by its presence in a certain field of s.p.a.ce. Dr. Hussey, in 1834, wrote to Sir George Biddell Airy, astronomer royal at Greenwich, suggesting that the perturbation of the orbit of Ura.n.u.s might be used as the clew for the discovery of the planet beyond. But Sir George was one of those safe, conservative scholars who scorn to follow the suggestions of genius, preferring rather to explore only what is known already. He said in answer that he doubted if the irregularity in the Uranian orbit was in such a state of demonstration as to give any hope of the discovery of the disturbing cause. He doubted even that there was such irregularity in the Uranian orbit. He was of opinion that the observers had been mistaken in the alleged detection of perturbations. So the Greenwich observatory was not used on the line of exploration suggested by Hussey.

Three years afterward, and again in 1842, Sir George received letters from the younger Bouvart, again suggesting the possibility and probability of discovering the ultra-Uranian planet. These hints were strengthened by a letter from Bessel, of Konigsberg. But Sir George B.

Airy refused to be led in the direction of so great a possibility.

It was in 1844 that Professor James Challis, of the Cambridge observatory, appealed to Sir George for the privilege of using or examining the recorded observations made at Greenwich of the movements of Ura.n.u.s, saying that he wished these tables for a young friend of his, Mr. John C. Adams, of Cambridge, who had but recently taken his degree in mathematics. Adams was at that date only twenty-five years of age. The royal astronomer granted the request, and for about a year Adams was engaged in making his calculations. These were completed, and in September of 1845, Challis informed Sir George Airy that according to the calculations of Adams the perturbations of Ura.n.u.s were due to the influence of an unknown planet beyond.

The young mathematician indicated in his conclusions at what point in the heavens the ultra-Uranian world was then traveling, and where it might be found. But even these mathematical demonstrations did not suffice to influence Sir George in his opinions. He was an Englishman!

He refused or neglected to take the necessary steps either to verify or to disprove the conclusions of Adams. He held in hand the mathematical computations of that genius from October of 1845 to June of the following year, when the astronomer Leverrier, of Paris, published to the world his own tables of computation, proving that the disturbances in the orbit of Ura.n.u.s were due to the influence of a planet beyond, and indicating the place where it might be found. There was a close agreement between the point indicated by him and that already designated by Adams.

It seems that this French publication at last aroused Sir George Airy, who now admitted that the calculations of Adams might be correct in form and deduction. He accordingly sent word to Professor Challis to begin a search for the unknown orb. The latter did begin the work of exploration, and presently saw the planet. But he failed to recognize it! There it was; but the observer pa.s.sed it over as a fixed star. As for Leverrier, he sent his calculations to Dr. Galle, of Berlin; and that great observer began his search. On the night of the twenty-third of September, 1846, he not only _saw_ but _caught_ the far-off world.

There it was, disc and all; and a few additional observations confirmed the discovery.

Hereupon Sir George Airy broke out with a claim that the discovery belonged to Adams. He was able to show that Adams had antic.i.p.ated Leverrier by a few months in his calculations; but the French scholars were able to carry the day by showing that Adams' work had been void of results. The world went with the French claim. Adams was left to enjoy the fame of merit among the learned cla.s.ses, but the great public fixed upon Leverrier as the genius who did the work, and Dr.

Galle as his eye.

Several remarkable things followed in the train. It was soon discovered that both Leverrier and Adams had been favored by chance in indicating the field of s.p.a.ce where Ura.n.u.s was found. They had both proceeded upon the principle expressed in Bode's Law. This law indicated the place of Neptune as 38.8 times the distance of the earth from the sun. A verification of the result showed that the new-found planet was actually only thirty times as far as the earth from the sun. In the case of all the other planets, their distances had been remarkably co-incident with the results reached by Bode's Law; but Ura.n.u.s seemed to break that law, or at least to bend it to the point of breaking--a result which has never to this day been explained.

It chanced, however, that at the time when the predictions of Leverrier and Adams were sent, the one sent to Galle and the other to Challis, Ura.n.u.s and the earth and the sun were in such relations that the departure of the orbit of Ura.n.u.s from the place indicated by Bode's Law did not seriously displace the planet from the position which it should theoretically occupy. Thus, after a little searching, Challis found the new world, and knew it not; Galle found it and knew it, and tethered it to the planetary system, making it fast in the recorded knowledge of mankind.

While Daniel O'Connell, the greatest Irishman of the present century, despairing of the cause of his country, lay dying in Genoa, and while Zachary Taylor, at the head of a handful of American soldiers was cooping up the Mexican army in the old town of Monterey, a new world, 37,000 miles in diameter and seventeen times as great in ma.s.s as the little world on which we dwell, was found slowly and sublimely making its way around the well nigh inconceivable periphery of the solar system!

EVOLUTION OF THE TELESCOPE.

The development of telescopic power within the present century is one of the most striking examples of intellectual progress and mastery in the history of mankind. The first day of the century found us, not, indeed, where we were left by Galileo and Copernicus in the knowledge of the skies and in our ability to penetrate their depths, but it did find us advanced by only moderate stages from the sky-lore of the past.

The after half of the eighteenth century presents a history of astronomical investigation and deduction which confirmed and amplified the preceding knowledge; but that period did not greatly widen the field of observation. If the sphere of s.p.a.ce which had been explored on the first day of January, 1801, could be compared with that which is now known and explored by our astronomers, the one sphere would be to the other even as an apple to the earth.