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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



A EING OF WOKLDS. 



THREE hundred years ago, when what was 

 called the Copernican Paradox was strug- 

 gling for existence against the then orthodox 

 Ptolemaic astronomy, the solar system was sup- 

 posed to consist of eight bodies. The followers 

 of Copernicus believed in a central sun, round 

 which six orbs revolved, while around one of 

 these — our earth — traveled one other orb — mak- 

 ing (with the central sun) eight bodies in all. The 

 followers of the old astronomy, including at that 

 time nine-tenths of the astronomers of repute, 

 believed in a central earth, round which traveled 

 seven planets, the sun and moon being two of 

 these, only distinguished from the rest (as plan- 

 ets) by the comparative simplicity of their move- 

 ments. During last year the number of bodies 

 forming the solar system, without including com- 

 ets or meteorites, or the multitudinous satellites 

 which compose the ring of Saturn, has been 

 raised to 200 — so that for every orb known in 

 the days of Copernicus and his first followers, 

 twenty-five are now recognized by astronomers. 

 Year after year more are becoming known to us. 

 In fact, planets are being discovered so fast, that, 

 after an effort (by dividing the watch upon them 

 among the leading observatories) to keep them 

 well under survey, the task has become regarded 

 as almost hopeless. One or two of the flock are 

 already missing ; and it seems not improbable 

 that, before many years have passed, twenty or 

 thirty planets will have to be described as miss- 

 ing, while endless controversies may possibly 

 arise, respecting those newly discovered each 

 year, on the delicate question whether a dis- 

 covery or a rediscovery has been effected. 



It is hardly necessary to say, perhaps, that 

 we refer to that strange ring of small planets 

 which travels between the paths of Mars, the 

 miniature of our earth, and Jupiter, the giant of 

 the solar system, as far surpassing our earth in 

 size as it is surpassed by the sun. In the wide 

 space between these two planets wander thou- 

 sands of tiny planets. They form a zone of di- 

 vision not only between Mars and Jupiter, thus 

 unlike each other, but between the family of 

 small planets of which our earth is the principal 

 member, and the family of large planets — Jupiter, 

 Saturn, Uranus, and Neptune. It is a strange 

 thought that for ages these bodies have been 

 circling round the sun unknown to men, though 



so near to us, compared with the fixed stars, that 

 from the nearest of these the whole ring, far 

 within which, be it remembered, the earth trav- 

 els, would appear as the merest point in space. 

 Still stranger is the thought that, among the 

 members of this system or ring of worlds utterly 

 invisible to ordinary eyesight, there must be pre- 

 sented at times, if living creatures are there to 

 see, some of the most remarkable celestial scenery 

 visible from any part of the solar system. For 

 the orbits of these bodies interlace in a strangely 

 complex manner. At times, from one or other of 

 the set, several of the rest must be seen at so 

 short a distance as to appear larger and more 

 conspicuous than Jupiter or Venus appears to 

 ourselves, while occasionally an even nearer ap- 

 proach must be made. In fact, in this part of 

 the solar system, and in this part alone, colli- 

 sions between planets are possible catastrophes ; 

 though, fortunately, the motions of these bodies 

 being always in the same direction, they cannot 

 encounter each other full tilt, but can only come 

 into collision by the swifter overtaking the slower. 

 Even of this there is little risk, so small are those 

 planets, and so enormous the ring of space in 

 which they travel. 



For many years the idea had been gaining 

 ground that those astronomers who were using 

 their telescopes in the search for small planets, 

 were wasting time which might be better em- 

 ployed. " Of what use," many asked, " can it be, 

 now that we know these bodies may be counted 

 by thousands, to search night after night for 

 hours on the chance of discovering a few each 

 year?" But recently it has %een seen that the 

 small planets may give us very useful infor- 

 mation. They have, in fact, already told us how 

 much their giant neighbor, Jupiter, would weigh 

 if he could be put in a scale against the earth — 

 or, rather (for that was already known), they 

 have shown us that Jupiter had been rightly 

 weighed in another way. And now it seems 

 likely that we shall learn from this despised 

 family the true measure of the sun's distance, | 

 and with that the scale of the solar system, the 

 quantity of matter contained by the sun, and 

 many other matters of great importance in as- 

 tronomy. 



As one of the longest known among the minor 

 planets has already given a very fair answer to 



