Among the privileged few to whom he had offered to exhibit his sidereal war-ship were Mr. and Mrs. Tassifer and, of course, Rhoda. It was a beautiful spring afternoon about two weeks after the conversation just recounted between the solicitor and his lady, and their chauffeur found great difficulty in threading his way among the crowds of people who had come out, as usual, to struggle for a glimpse of the famous machine that was going to essay a trip through space, not merely for the banal purposes of scientific discovery but actually to attack and alter the course of a celestial body. Finally having gained the gate without committing manslaughter, they found themselves on a flat parade-ground, in the center of which rested a gigantic, shining, circular tube, seventy-five feet in diameter and fifteen feet thick, built of aluminum plates, and surmounted by the superstructure which had been visible from outside, and which, as Bennie told them, bore the tractor that lifted the car. "It's the thing at the top shaped like an inverted thimble," he explained. "There's a big cylinder of metallic uranium inside, and we play our disintegrating rays on the under surface of this cylinder from those oblique tubes below. When the rays hit the uranium in the cylinder, the atoms explode, and the decomposition products are shot off downward at almost the velocity of light. A back pressure is thus produced which lifts the Ring exactly like a rocket." "How long does one of your cylinders last?" inquired Rhoda. "Atterbury--Pax's engineer, who came back with us--says that a cylinder is good for about a ten-hour run." "But you can't get very far out into space in ten hours, can you?" she queried. "What will you do when the cylinder is exhausted?" "I've figured out that we can get up a velocity of over fifteen miles a second with a one-hour run of the tractor," he answered. "If we then shut off the power, our momentum alone will carry us over fifty thousand miles during the next hour. So, you see, we can coast most of the way." One of the khaki-uniformed guards now detached and lowered a steel ladder and then climbed up and opened a round door in a sort of vestibule on the side of the Ring. "Now, Mrs. Tassifer," remarked Bennie, "that is the air-lock. It has double doors. When the car is in a vacuum, or beyond the earth's atmosphere, the contained air would all rush out into space if there were any direct communication with the outside. You enter the air-lock from the inside, close and bolt the inner door behind you, open the other door and step out, just as the divers leave and enter a submarine on the bottom of the ocean."