Page:The evolution of worlds - Lowell.djvu/129

Rh together. We see this in the arrangement of the orbits. If we plot the orbits of the asteroids, we shall be struck by the emergence of certain blanks in the ribbon representing sections of their path. It is the woof of a plaid of Jupiter's weaving. The gaps are where asteroids revolving about the Sun would have periods commensurate with his, $2⁄5$ ,$1⁄2$, $3⁄5$, $4⁄7$, and the like. Such bodies would return after a few revolutions, five of theirs, for instance, to Jupiter's two, into the same configurations with him at the same points of their orbits. Thus the same perturbation would be repeated over and over again until the asteroid's path was so changed that commensurability ceased to exist. And it would be long before perturbation brought it back again. Thus the orbits are constantly swinging out and in, all of them within certain limits, but those are most disturbed which synchronize with his. In this manner he has fashioned their arrangement and even prevented any large planet from forming in the gap.

Such restrictive action is not only at work to-day in the distribution of the asteroids and in the partitions of Saturn's ring, but it must have operated still more in the past while the system was forming. To Professor Milham of Williamstown is due the brilliant suggestion that this was the force that fashioned the planetary orbits. For a planet once given off from a