These small planets are all telescopic, invisible to the naked eye, with the exception of Vesta, and sometimes Ceres, which good sight can occasionally succeed in distinguishing; they are of the seventh, eighth, ninth, tenth, and eleventh magnitudes, and even still smaller, and it was for this reason also that so long an interval of time elapsed between the fourth and fifth discoveries. It is probable that all the small planets of any importance are now known, but that a great number—several hundreds, perhaps—still remain to be discovered of which the average brightness does not exceed that of stars of the twelfth magnitude, and of which the diameter is but a few miles. The diameter of the largest, Vesta, may be estimated at 400 kilometres (248 miles).
Hencke found successively the 5th and the 6th in 1845 and 1847; Hind, the English astronomer, the 7th and 8th in 1847; Graham, an English observer, the 9th in 1848; Gasparis, an Italian astronomer, the 10th and 11th in 1849 and 1850, and afterward seven others. Hind has further discovered eight others; Goldschmidt, a German painter (a naturalized Frenchman), discovered fourteen between 1852 and 1861.[27] They are now discovered by swarms; Paliser alone has found sixty-eight since 1874.
The names given to these small bodies commenced with the mythological army of divinities of the earth and ancient heaven; but even before the list had been exhausted certain scientific, or even national or political, circumstances caused the preference to be given to more modern names. It was thus that the 11th, discovered at Naples, received the name of Parthenope; the 12th, discovered in England, that of Victoria; the 20th, that of Massilia; the 21st, that of Lutetia; the 25th, that of Phocæa, before even Urania had been restored to the skies; the 45th was named in honor of the Empress of the French; the 54th, in honor of the illustrious Alexander von Humboldt; etc. The 87th, 107th, 141st, 154th, and 169th have been named in honor of a young astronomer who has devoted his best years to the culture of astronomy.
A rather curious fact is that they have put Wisdom (Sapientia) in the sky only at the 275th, discovered in 1888; Bellona has been placed there since the 28th (1854).
Of all this number of planets, the nearest to the sun is No. 149, Medusa, of which the distance is 2.17—that is to say, about twice as far from the sun as the earth; and the most distant is No. 279, Thule, of which the distance is 4.26, about 4¼ times our distance.
A large number of these small bodies are remarkable for their great eccentricity and for their high inclination to the ecliptic, an inclination so great that some of them leave the Zodiac; thus, Pallas (2) goes 34 degrees from the ecliptic; Euphrosyne (31) and Anna (265) and Istria (183), to 26 degrees. They are sometimes northern circumpolar stars, always above the horizon, sometimes southern stars, not arising above the horizon of Paris. All these orbits are so interlaced with each other that, if they were material hoops, we could by means of one or two taken by chance raise all the others.
Are they globes? Yes, doubtless, for the most part. But several among the smaller ones may be polyhedral, and may have proceeded from subsequent explosions; the variations of brightness which have been sometimes observed seem to imply surfaces irregularly broken.
Are they worlds? Why not? Is not a drop of water shown in the microscope peopled with a multitude of various beings? Does not a stone in a meadow hide a world of swarming insects? Is not the leaf of a plant a world for the species which inhabit and prey upon it? Doubtless among the multitude of small planets there are those which must remain desert and sterile because the conditions of life (of any kind) are not found united. But we can not doubt that on the majority the ever-active forces of nature have produced, as in our world, creations appropriate to these minute planets. Let us repeat, moreover, that for nature there is neither great nor little. And there is no necessity to flatter ourselves with a supreme disdain for these little worlds, for in reality the inhabitants of Jupiter would have more right to despise us than we have to despise Vesta, Ceres, Pallas, or Juno: the disparity is greater between Jupiter and the earth than between the earth and these planets.