The banging on the agricultural dome, _had to be stopped_! A hole would let in the gas! Rifles, that had been brought back on the ship as curiosities, were given to each earthman. They loaded them carefully while they searched for some means of reaching the trouble. When the leader of the dome heard what they were planning, he showed them sealed openings to a space between the sections of metal, which hadn't been used since the city was built. The dome was constructed in three layers, for insulation, and to give added protection. It was like a maze, to work their way toward the pounding through the network of struts. At times they had to crawl on their hands and knees, at others there were clearly defined passages. They were afraid, and not ashamed to show it. They were hunting creatures which they knew nothing about--didn't even know whether bullets would affect them! They might face thinking beings, or forms of life that only wanted to search in the domes for food. It was not a pleasant thought. Every rifle was cocked as they neared the source of the pounding. Every nerve drawn to the finest point. Suddenly Dick stopped. He was ahead of the others and first to glimpse what they faced. He motioned to use the oxygen masks, as he fastened his own in place. As they crept closer, light glinted on the giant pointed hammer, operated from beyond the outer layer of metal. It rose and fell at even intervals, through the rent in the upper surface. The ram had already crushed through two thicknesses of metal, and was battering at the inner layer. The inside section was more like glass than metal and dim light passed through, but the outer layers were opaque. When the huge ram disappeared from the glow of light it left a gaping hole where it had been. It was of material they had never seen and glistened with a brownish hue. It appeared to shorten and expand in diameter, each time it struck the surface. For a moment they hesitated, trying to decide the best means of attack. Whatever animated the ram was above their vision, and they had to be close to the opening to see it. Each time the shiny object descended, the dome vibrated beneath their feet. As long as the vibration remained they were safe, but when it felt like a thud--the metal would be cracking! Thousands of helpless people were depending on the action of earthmen, for their future existence. They seemed to think that it was only necessary to _tell_ their troubles to these amazing strangers, to have them solved. Stories about the use of water to drive the space ship, had circulated throughout the cities, crediting the newcomers with superhuman powers. As the little party crept nearer, they separated, to approach the opening from every direction. Dick was to fire first--if he saw anything to shoot at! It might be a powerful machine, clamped to the outer surface, instead of a being that could be injured. The glass globes of the masks were clouding with moisture, and it was hard to see.