Six days after that momentous meeting of the council, a mighty fleet of air-boats rose and circled above the city. The character of the invisible force-shield above the city had been altered to allow the passage of any air-boat through it, and now no less than five hundred of the air-boats hovered over Kom. In design they were much like the ones I had vaguely glimpsed in the city of cylinders, long and flat and narrow, pointed at either end and with a low wall around their sides for the protection of their occupants. The people of Kom had worked wonders in those six days, thus to construct half a thousand of the flying cars, and to equip them with a time-wave apparatus like our own. Every car was thus equipped, the apparatus on each being a direct copy of that in our own car. Lantin and I still clung to our own car, however, which had been overhauled for us by the scientists of Kom after our crash, and which was unhurt by the collision. And most of our time, during that period, had been engaged in directing the manufacture of the time-traveling apparatus, and teaching a selected few the operation of it. These few, in turn, taught many others, and by the time we were ready for our start, there was at least one man on each air-boat who understood the time-wave mechanism. The plans of our expedition were simple enough. We were to drop down on the city of cylinders, destroy it utterly, and annihilate both the Kanlars and the Raider, if possible. I think that in reality none of the members of our expedition had any real desire to meet the Raider, but I knew that in spite of the fear they had of him, they would obey the orders of Kethra without faltering. I knew but little of the weapons which the scientists of Kom had furnished to the occupants of the air-boats. Kethra had spoken to us of a sound-ray, an intense beam of sound-vibrations which, directed on some object, could be changed in frequency until it matched that object's frequency of vibration, which would result in the destruction of the thing so focused on. It was the principle of two tuning-forks, which will cause each other to vibrate across a great distance, if of the same period of vibration. I had heard mention of other weapons, also, designed to combat the Raider, but had seen none of these. Now, as the great fleet hovered and circled above the white city of Kom, with our own time-car poised above the fleet, a single large air-boat drove up through the mass of the others and hung beside us. It was the car of Kethra, a long, black one, and near its pointed prow stood the white-robed leader himself. He bent, spoke an order into a mouthpiece, and then his car slanted up and northward, with swiftly increasing speed, while the great fleet below did likewise, his order being communicated by a form of radio to every air-boat. Still hanging beside the car of Kethra, our own time-car raced along, since we were to guide the fleet toward the city of cylinders.