A MXG OF WORLDS. 



471 



effecting the rediscovery on January 1, 1802. 

 Thus, the first night of the present century was 

 distinguished by the discovery of a new planet, 

 and, before the first year of the century had 

 passed, the planet was fairly secured. 



Piazzi, the discoverer of the planet, assigned 

 to it the name of the titular goddess of Sicily, 

 where the discovery was made — Ceres. 



Ceres was found to be traveling in an orbit 

 corresponding in the most satisfactory manner 

 with Bode's law. According to that law the 

 missing planet's distance from the orbit of Mer- 

 cury should have been 24 ; calling Mercury's dis- 

 tance from the sun 4, the actual distance of Ceres 

 is 23J. 



Yet astronomers were not satisfied with the 

 new planet. It traveled at the right mean dis- 

 tance from the sun; but, passing over its infe- 

 riority to its neighbors, Mars and Jupiter, in size 

 and splendor, it moved in most unplanetary 

 fashion. Instead of traveling nearly in the same 

 plane as the earth, like its neighbors Mars and 

 Jupiter, its path was inclined to that plane in an 

 angle of more than 10° — a thing as yet unheard 

 of among planets. As to its size, Sir W. Uer- 

 schel, from measurements made with his power- 

 ful telescopes, estimated the new planet's diame- 

 ter at about 160 miles, so that, supposing it of 

 the same density as our earth, its mass is less 

 than x^s'uoo part of hers. Thus, it would take 

 more than 1,560 such planets to make a globe as 

 massive as our moon. And even this probably 

 falls far short of the truth. For our earth owes 

 no small part of her density to the compression 

 produced by the attractive energy of her own 

 substance. The moon, which is less compressed, 

 has jnuch smaller density ; in fact, little more 

 than half the earth's. Mars, again, being smaller, 

 and having less attractive energy, has less densi- 

 ty than the earth (his density is about -fo of hers). 1 

 The tiny Ceres would be very much less com- 

 pressed, and, if made of the same substances, 

 as we may well believe, would probably have a 

 density less than half the moon's, or not very 

 much exceeding that of water. Thus, it would 

 probably take some half-million of worlds like 

 Ceres to make such a globe as our earth, while 



1 Of course, the giant planets Jupiter, Saturn, Ura- 

 nus, and Neptune, seem to present exceptions to the 

 rule we have here indicated. But there can be no 

 doubt that in their case intense heat expands the 

 planets' substance, while in reality we have no means 

 of forming an opinion respecting their real density, 

 since the surfaces we measure are not the real sur- 

 faces, but layers of clouds enwrapping these planets, 

 and lying who shall say how far from the solid surface ? 



from our moon six thousand such worlds as Ceres 

 might be made. It was natural that astronomers 

 should regard with some suspicion a planet falling 

 so far short of every known planet, and even of 

 a mere moon, in size and mass. 



But presently a discovery was made which 

 still more markedly separated Ceres from the 

 rest of the planetary family. Olbers, during his 

 search for Ceres, had had occasion to study very 

 closely the arrangement of the groups of small 

 stars scattered along the track which Ceres might 

 be expected to follow. What reason he had for 

 continuing his examination of these groups after 

 Ceres was found does not appear. Possibly he 

 may have had some hope of what actually oc- 

 curred. Certain it is that in March, 1802, or 

 nearly three months after Ceres had been redis- 

 covered, he was examining a part of the constel- 

 lation Virgo, close by the spot where he had 

 found Ceres on January. 1st, in the same year. 

 While thus at work, he noticed a small star 

 forming with two others, known by him, an equi- 

 lateral triangle. He felt sure this star had not 

 been there three months before, and bis first idea 

 was that it was a variable star. At the end of 

 two hours, however, he perceived that it had 

 moved slightly toward the northwest. On the 

 next evening it had moved still farther toward 

 the northwest. It was, in fact, a planet, and, to 

 the amazement of astronomers, the study of this 

 planet's motion showed that its mean distance 

 from the sun differed very little from that of Ce- 

 res. We speak of the amazement of astrono- 

 mers, because the fact thus discovered was, in 

 reality, the most surprising of any which had been 

 made known to them since the nature of Saturn's 

 ring was discovered by Iluygens in 1656. We 

 have become so accustomed of late to the dis- 

 covery of planets traveling along the region of 

 space between the paths of Mars and Jupiter, 

 that we are apt to forget how strange the circum- 

 stance must have appeared to astronomers at the 

 beginning of the present century, that the old 

 views respecting the solar system were errone- 

 ous, and that, in addition to the planets traveling 

 singly around the sun, the existence of a ring of 

 planets must be admitted. It is true that the 

 discovery of this second planet (to which the 

 name Pallas was given) did not fully demonstrate 

 this. Still it showed that Ceres was not traveling 

 alone in the region which had so long been sup- 

 posed untenanted. And as it seemed in some de- 

 gree to explain the smallness of Ceres, suggesting 

 the idea that possibly the combined mass of 

 bodies traveling in this space might not be great- 



