G.K. Green, a senior physicist at Brookhaven National Laboratory on Long Island, N.Y., discusses the cosmotron, an atom smasher made possible by the Atomic Energy Commission and operated by nine universities, including Johns Hopkins. Mr. Green first explains that carbon atoms form charcoal and diamonds and that the nucleus of carbon consists of half neutrons and half protons. He then shows a model of a ring-shaped cyclotron, a slice of the magnet and vacuum chamber within, and a film of the actual machine in operation. A Van de Graaff generator, a particle accelerator, shoots protons into the vacuum chamber of the magnet, and they build up speed with each rotation up to 4 million revolutions per second. At 180,000 miles per second, the protons collide with a target resulting in mesons, medium weight particles. Mr. Green also shows a film of a cloud chamber in which atomic particles leave vapor trails. He says the purpose of the cosmotron is to probe the center of the atom.