And then he noticed something else. No matter where the trees stood, no matter in what direction from the laboratory, they all bent inward toward the building ... and the whining, thundering, shrieking machine. Inside the laboratory an empty bottle crashed off a table and smashed into a thousand fragments. The tinkling of the broken glass was a silvery, momentary sound that protested against the blasting thrum of power that shook the walls. Manning fought along the floor to Russ's side. Russ roared in his ear: "Gravitational control! Concentration of gravitational lines!" The papers on the desk started to slide, slithering onto the floor, danced a crazy dervish across the room. Liquids in the laboratory bottles were climbing the sides of glass, instead of lying at rest parallel with the floor. A chair skated, bucking and tipping crazily, toward the door. * * * * * Russ jerked the power lever back to zero. The power hum died. The liquids slid back to their natural level, the chair tipped over and lay still, papers fluttered gently downward. The two men looked at one another across the few feet of floor space between them. Russ wiped beads of perspiration from his forehead with his shirt sleeve. He sucked on his pipe, but it was dead. "Greg," Russ said jubilantly, "we have something better than anti-gravity! We have something you might call _positive_ gravity ... gravity that we can control. Your grandfather nullified gravity. We've gone him one better." Greg gestured toward the machine. "You created an attraction center. What else?" "But the center itself is not actually an attracting force. The fourth dimension is mixed up in this. We have a sort of fourth-dimensional lens that concentrates the lines of any gravitational force. Concentration in the fourth dimension turns the force loose in three dimensions, but we can take care of that by using mirrors of our anti-entropy. We can arrange it so that it turns the force loose in only one dimension." Greg was thoughtful for a moment. "We can guide a ship by a series of lenses," he declared at last. "But here's the really important thing. That field concentrates the forces of gravity already present. Those forces exist throughout all of space. There are gravitational lines everywhere. We can concentrate them in any direction we want to. In reality, we fall toward the body which originally caused the force of gravitation, not to the concentration." * * * * *