"There's something wrong!" he shouted to Burke. "We're way off our course!" "What's happened?" yelled Atterbury, shooting, in his favorite posture, feet foremost, out of the condenser-room. "We're running all cock-eyed! Look where the sun is--the earth!" "They ought to be nearly in line," replied Burke, in a confused way. "There's some new influence at work here." "But I've lost Medusa entirely!" Hooker called down to them. "I can't imagine what's up. Of course, we left the earth with its axial and orbital velocities as well as our own. I thought I'd worked it out all right, but I must have overlooked something. Anyhow, the first thing to do is to get back on our course. Atterbury, start up your engines half-speed; I'll call to you when I want your whole force. Burke, you must slant the tractor over and turn the Ring until we are pointing toward Medusa. I don't know just how she'll act, but I think we can tip her almost any way we please. When we're pointed in the right direction, we'll straighten out the tractor and give her full-speed ahead. Are you ready?" Atterbury darted back toward the condenser-room, and almost immediately the hum of the dynamo began again. With its resumption, their weight returned, but hardly enough to enable them to walk in comfort. "Ah," exclaimed Burke, "It sure feels good to be on foot again! I was getting darn tired of this spook business." Under Hooker's directions, he moved the control-lever until Medusa swam again into the field of the telescope. Then, as the green star neared the center of the lens, Bennie ordered him to straighten the course and directed Atterbury to turn on full-speed. The noise of the machinery increased, and with it came a further increase in their weight. The whole force of the tractor was again pressing them on toward their distant goal. Bennie once more descended from the observation-cage and took his place beside Rhoda at the deadlight on the floor of the car. Hypnotized by the wonder and beauty of the crescent earth beneath them, they hardly noticed that it was gradually shifting its place. Suddenly, it slipped entirely out of sight. "Hang it!" shouted Bennie, in despair. "We've lost control of the Ring!" Where, before, the earth had been, there now appeared the stupendous disk of the full moon. At the same moment, Burke uttered an exclamation of fear. "We're all out of kilter!" he cried. "I was looking down through the observation-window at the earth, and--all of a sudden it wasn't there!" "The Ring is evidently slowly turning over," stammered Bennie. "If our tractor were not running, it wouldn't matter, but our direction must now be changing from moment to moment. We may have been captured or pulled out of our course by the moon! It's pretty near us, and you know how Jupiter changes the orbits of the comets that pass near it." At that moment, Atterbury appeared in the doorway.