Page:The Solar System - Six Lectures - Lowell.djvu/38



if not my very first, is of such an one, and the memory of it has never been approached by any celestial phenomenon since. A total eclipse of the Sun is commonplace beside it. Of the four hundred up to now observed, the greater part move in orbits differing so little from the parabolic for the small fraction of their paths we are privileged to mark that to all intent they travel in parabolas. They lean, however, to the side of the ellipse. Most of them frankly do so, although so slightly that to determine their major axes to any degree of accuracy is not possible. Very few, three or four perhaps, hint at hyperbolas. Not one is such beyond question, however slightly. In my notes on Galle's catalogue, I find the following gloss at the end of the list: "There is not a single undisputed hyperbolic orbit; nor is there one in which the computed non-hyperbolic orbits are not in the majority."

From this fact of a practical parabolicity of path many astronomers have argued the exterritoriality of these bodies, and early in the last century Laplace set himself the problem of finding the probability of hyperbolic to elliptic orbits on the theory that they all came to the Sun from stellar space. In spite of several mistakes in his work, first pointed out by Gauss, he reached a