PLANETOIDS, the name given to a great group of minute planets placed to gether between Mars and Jupiter. Professor Titius, of Wittenberg, having drawn attention in 1772 to the fact that, with the exception of Jupiter, each planet has an orbit just about double that near est to it on the side of the sun, Professor Bode, of Berlin, drew the natural infer ence that the one exception to the rule would probably be removed by the dis covery of a planet less remote from the sun than Jupiter, and more distant than Mars. On Jan. 1, 1801, a planetary body, afterward called Ceres, was found by Piazzi in the part of the solar system theoretically indicated; it was, however, far more diminutive in size than had been expected. Within the next six years three more asteroids (Pallas, Juno, and Vesta) were found in proximity to Ceres. Up to October, 1903, 542 small planets had been discovered, 70 by Americans. All are of minute size, and
some angular in place of spherical.
The term asteroid, applied to these small bodies, is now becoming obsolete, the appellation minor planets taking its place. They are sometimes also called extra-zodiacal planets, from their orbits stretching outside the zodiac, which is not the case with those of the normal type. Authorities differ respecting some minute points in the list of asteroids. Melete, when discovered on Sept. 9, 1857, was mistaken for Daphne, an error not detected till January, 1859. Herschel, Proctor, etc., number it 56, and place the date 1857, where it offends the eye, in 1859; others, with Mr. G. F. Chambers, transfer it to 1857, which alters the numbering of all the minor planets from 47 to 56. There are other minute differ ences between lists of asteroids by lead ing authorities.