With an odd persistence, though, the question continued to trouble my thoughts in the hours that followed, and when we finally swept in toward the solar system twelve hours later, it was with a certain abstractedness that I watched the slow largening of the yellow star that was our sun. Our velocity had slackened steadily as we approached that star, and we were moving at a bare one light-speed when we finally swept down toward its outermost, far-swinging planet, Neptune, the solar system's point of arrival and departure for all interstellar commerce. Even this speed we reduced still further as we sped past Neptune's single circling moon and down through the crowded shipping-lanes toward the surface of the planet itself. Fifty miles above its surface all sight of the planet beneath was shut off by the thousands of great ships which hung in dense masses above it--that vast tangle of interstellar traffic which makes the great planet the terror of all inexperienced pilots. From horizon to horizon, it seemed, the ships crowded upon each other, drawn from every quarter of the Galaxy. Huge grain-boats from Betelgeuse, vast, palatial liners from Arcturus and Vega, ship-loads of radium ores from the worlds that circle giant Antares, long, swift mail-boats from distant Deneb--all these and myriad others swirled and circled in one great mass above the planet, dropping down one by one as the official traffic-directors flashed from their own boats the brilliant signals which allowed a lucky one to descend. And through occasional rifts in the crowded mass of ships could be glimpsed the interplanetary traffic of the lower levels, a swarm of swift little boats which darted ceaselessly back and forth on their comparatively short journeys, ferrying crowds of passengers to Jupiter and Venus and Earth, seeming like little toy-boats beside the mighty bulks of the great interstellar ships above them.