280

THE MINOR PLANETS.

supposing their average diameter to he as we have suggested,and their density the same as that of the Earth , the actualnumber of the Minor Planets may he 1,100 times as great as229 ; i.e., it may exceed 250,000. But if they are for themost part far smaller than those which we have been able tosee;—in fact, so small that they will ever remain invisible evenin our largest telescopes ;—and not only so, but also of lighterdensity than we have supposed, it is by no means impossiblethat they may amount to several millions in number.

In a recent communication to the Vienna Academy , HerrHornstein has stated some reasons for believing that thediameter of most of those discovered of late years lies between5 and 15 miles ; and that, by an increase of telescopic power,we may probably detect many additional ones of this size inthe outer parts of the zone in which they are found. At thesame time, he thinks that the great majority of those inexistence, whose orbits lie nearer to that of Mars than tothat of Jupiter , have already been detected; and that thereare not many in that region, of still smaller size, whichincreased instrumental means would show.

In quoting these various statistics, we have endeavoured, inaccordance with our previously stated intention, to select, outof the mass of figures that lies before us, such as are bothimportant in themselves, and may also he useful in our discus-sion of the question to which we now proceed; viz.,—What isthe probable origin of this remarkable group of bodies ?

It is true that in some respects we know but little aboutthem; but we find that they are to be numbered by hundreds,if not by thousands, or even by millions. One is found to come5,000,000 miles within the orbit of Mars ; another travelsto a distance from the Sun which is equal to about ji-ths ofthe mean distance of the mighty planet Jupiter . With fewexceptions they are exceedingly small. Their orbits for themost part are of moderate eccentricity, and of moderateinclination to the plane of the ecliptic; but they occasionallyexhibit an unusually erratic form and position. We certainlyare not justified in speaking of these minor members of theSun’s family as a ring of planets. They may, so far as we