The men who had gathered in the secret room were some of the finest scientists in the world. The leader of the group was Enrico Fermi (En-REE-ko FER-mee), an Italian scientist who had come to the United States. For some weeks the men had been quietly at work, carefully stacking a huge pile of pure graphite bricks. Here and there among the bricks they placed pieces of uranium. Fermi believed that when the pile reached a certain size, a chain reaction would start. By December 2, the size seemed to be right. [Illustration] Inside the pile were three control rods. They were made of cadmium, an element which soaks up flying neutrons like a sponge. With the rods in place, no reaction could take place. When the rods were withdrawn, the reaction would begin. To make sure that the pile would not get out of hand, the three control rods were operated in three different ways. The first one was controlled by an electrical switch and was completely automatic. The second, called ZIP, was tied to a rope in the balcony. In case of emergency, there was a man ready with an axe. He had only to chop the rope and ZIP would go crashing back into the pile. The third rod was moved by hand. It was time to begin. Fermi gave the signal for the automatic rod to be withdrawn. Immediately, the counters which measured radioactivity began to tick. Then Fermi gave the command, "ZIP out!" ZIP was drawn up on its balcony rope and the ticking of the counters at once became faster. Then Fermi turned to the man who controlled the last rod. This rod was marked in feet and inches, and Fermi said: "Pull it out to thirteen feet." All eyes were on the instruments. Not yet. A little more. Pull it out another foot. Not yet. The men grew more and more tense as the careful work went on. [Illustration] Finally, at about 3:25 in the afternoon, Fermi made a last check of his instruments and his calculations. Then he said: "Pull it out another foot. This is going to do it!" No one dared breathe. The ticks of the counters became so rapid they sounded like a steady hum. The pointers on the instruments swung all the way over--and stayed there. The first atomic chain reaction had been achieved! The pile was allowed to run for 28 minutes. Then the control rods were put back. Suddenly, all was quiet. There were no ticks from the counters. Not only had these men started a chain reaction, they had also been able to stop it. At last man could control the energy of the atom. One of the men present, Arthur H. Compton, ran to the phone to call James B. Conant, chairman of the U. S. National Defense Research Committee. But since our country was at war in 1942, it wasn't safe to talk about this important secret over the telephone. And so, on the spur of the moment, a quick-witted and historic conversation took place. Compton said: "Jim, you'll be interested to know that the Italian navigator has just landed in the new world."