[Illustration: _Tenth layer of graphite blocks containing pseudospheres of black and brown uranium oxide. The brown briquets, slightly richer in uranium, were concentrated in the central area. On the right is the nineteenth layer of graphite covering layer 18 containing slugs of uranium oxide._] One by one the cadmium rods were pulled out. The number of uranium atoms undergoing fission each second rose and, finally, at 3:45 p.m., the uranium fission became self-sustaining. It kept going on its own (with the cadmium rods ready to be pushed in if it looked as though it were getting out of hand—something calculations showed was not likely). News of this success was announced to Washington by a cautious telephone call from Arthur Holly Compton (1892-1962) to James Bryant Conant (1893- ). “The Italian navigator has landed in the new world”, said Compton. Conant asked, “How were the natives?”, and the answer was, “Very friendly”. This was the day and moment when the world entered the “nuclear age”. For the first time, mankind had constructed a device in which the nuclear energy being given off was greater than the energy poured in. Mankind had tapped the reservoirs of nuclear energy and could put it to use. Had Rutherford lived but 6 more years, he would have seen how wrong he was to think it could never be done. The people of earth remained unaware of what had taken place in Chicago and physicists continued to work toward the development of the nuclear bomb. Enriched uranium was successfully prepared. Critical sizes were brought low enough to make a nuclear bomb small enough to be carried by plane to some target. Suppose one had 2 slabs of enriched uranium, each below critical size, but which were above critical size if combined. And suppose an explosive device were added that, at some desired moment, could be set off in such a way that it would drive 1 slab of enriched uranium against the other. There would be an instant explosion of devastating power. Or suppose the enriched uranium were arranged in loosely packed pieces to begin with so that the flying neutrons were in open air too often to maintain the chain reaction. A properly arranged explosion might compress the uranium into a dense ball. Neutron absorption would become more efficient and again, an explosion would follow. [Illustration: _Nuclear Fission of Uranium: A neutron hits the nucleus of an atom of uranium. The neutron splits the nucleus into two parts and creates huge amounts of energy in the form of heat. At the same time other neutrons are released from the splitting nucleus and these continue the fission process in a chain reaction._] On July 16, 1945, a device that would result in a nuclear explosion was set up near Alamogordo, New Mexico, with nervous physicists watching from a safe distance. It worked perfectly; the explosion was tremendous.