Dick stumbled against the lowest step of an invisible flight. The breeze was cut off, showing that they had entered a building. Underneath was a large oval of bare ground. Dick found a handrail and groped his way up around a spiral staircase, four flights of it. "Here is a room!" * * * * * Dick saw that widening edge of door again. The room inside was perfectly visible, though it seemed to be supported upon air. It was a spheroid, of huge size, with a number of large windows set into the walls, and it was filled with machinery. About a dozen workmen in blue blouses were moving to and fro, attending to what appeared to be a number of enormous dynamos, but there were other apparatus of whose significance Dick was ignorant. The dynamos were whirring with intense velocity, but not the slightest sound was audible. Von Kettler stepped to a switch attached to a stanchion of white metal, surmounted by a huge opaque glass dome, and threw it over. Instantly the hum and whir of machinery became audible, the sound of footsteps, the voices of the workmen, and the creak of boards beneath their feet. "You see, we have discovered the means of destroying sound waves as well as shadows, and it was a much simpler feat," said Von Kettler with a sneer. "Tell them that when you get back to Washington, Yankee pig. Also you might be interested to know that most of your bombs fell on camouflaged structures that we had erected with the intention of deceiving you." He gestured to Dick to precede him, and halted him at a plain round iron pipe or rod that rose up through the floor and passed through the roof. It was surrounded by a mesh of fine wire. Attached to it were various gauges, with dials showing red and black numbers. "This is perhaps our greatest achievement, swine," remarked Von Kettler, affably. "You shall see its operations from above." He pointed to a narrow spiral staircase rising at the far end of the room. "It is the practical application of Einstein's gravitation and electricity in field relation. It is by means of this, and the three dynamos on the ground that we were able to neutralize your engines last night and bring them down where we wanted them. You must be sure to tell the Washington hogs about that." * * * * * He motioned to Dick to cross the room and ascend the spiral staircase. Following him, he flung another switch similar to the first one, and instantly all sound within the room was cut off. They ascended the winding flight and emerged upon a floor or platform. Dick felt it under his feet, but he could see nothing except the ground, far beneath him. He seemed to be suspended in the void. He stopped, groping, hesitating to advance. Von Kettler's jarring laugh grated on his ears. "Don't be afraid, swine," he jeered. "This place is enclosed. There is a shadow-breaking device on every floor, which renders us complete masters of camouflage."