The mean distances of the minor planets between Mars and Jupiter vary from 2·20 to 3·49. The breadth of the zone is therefore 20,000,000 miles greater than the distance of the earth from the sun; greater even than the entire interval between the orbits of Mercury and Mars. Moreover, the _perihelion_ distance of some members of the group exceeds the _aphelion_ distance of others by a quantity equal to the whole interval between the orbits of Mars and the earth. The _Olbersian_ hypothesis of the origin of these bodies seems thus to have lost all claim to probability.[30] Professor Alexander's theory of the disruption of a primitive discoidal planet of great equatorial diameter, is less objectionable; still, however, it requires confirmation. But whatever may have been the original constitution of the ring,[31] its existence in its present form for an indefinite period is unquestioned. Let us then consider some of the effects of its secular perturbation by the powerful mass of Jupiter. _Portions of the ring in which the periods of asteroids would be commensurable with that of Jupiter._--The breadth of this zone is such as to contain several portions in which the periods of asteroids would be commensurable with that of Jupiter. As in the case of the perturbation of Saturn's ring by the interior satellites, the tendency of Jupiter's influence would be to form gaps or chasms in the primitive ring. The mean distance of an asteroid whose period is 1/2 that of Jupiter =3·2776 That of one whose period is 1/3 of Jupiter's =2·5012 " " 2/5 " =2·8245 " " 2/7 " =2·2569 " " 3/7 " =2·9574 " " 4/9 " =3·0299 For the purpose of facilitating the comparison of these numbers with the mean distances of the asteroids and of observing whether any order obtains in the distribution of these mean distances in space, we have arranged the minor planets, in the following table, in the consecutive order of their periods: Periods and Distances of the Asteroids.