VOLUME 3 Nuclear Fission 117 New Elements 117 The Discovery of Fission 122 The Nuclear Chain Reaction 127 The Nuclear Bomb 131 Nuclear Reactors 141 Nuclear Fusion 147 The Energy of the Sun 147 Thermonuclear Bombs 149 Controlled Fusion 151 Beyond Fusion 159 Antimatter 159 The Unknown 164 Reading List 166 [Illustration: _A total eclipse of the sun._] INTRODUCTION In a way, nuclear energy has been serving man as long as he has existed. It has served all of life; it has flooded the earth for billions of years. The sun, you see, is a vast nuclear engine, and the warmth and light that the sun radiates is the product of nuclear energy. In order for man to learn to produce and control nuclear energy himself, however (something that did not take place until this century), three lines of investigation—atoms, electricity, and energy—had to develop and meet. We will begin with atoms. ATOMIC WEIGHTS As long ago as ancient Greek times, there were men who suspected that all matter consisted of tiny particles which were far too small to see. Under ordinary circumstances, they could not be divided into anything smaller, and they were called “atoms” from a Greek word meaning “indivisible”. It was not until 1808, however, that this “atomic theory” was really put on a firm foundation. In that year the English chemist John Dalton (1766-1844) published a book in which he discussed atoms in detail. Every element, he suggested, was made up of its own type of atoms. The atoms of one element were different from the atoms of every other element. The chief difference between the various atoms lay in their mass, or weight.[1] Dalton was the first to try to determine what these masses might be. He could not work out the actual masses in ounces or grams, for atoms were far too tiny to weigh with any of his instruments. He could, however, determine their relative weights; that is, how much more massive one kind of atom might be than another.