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Fission v. Fusion. The new-style "fusion" of hydrogen and the old-style "fission" of uranium have a family resemblance. Both depend on the odd and unexplained fact that atomic nuclei do not weigh as much as the sum of the individual nucleons (protons and neutrons) which they contain. It is as if a dozen apples in a paper bag did not weigh as much as the same apples spilled out on the kitchen table and weighed separately...
Even more oddly, some large nuclei (e.g., uranium) weigh more than two-middle-sized nuclei containing between them an equal number of nucleons. It is as if a bushel basket of apples lost weight when the apples were put into two baskets...
Uranium fission works by dividing large "bushel basket" nuclei. When a uranium nucleus splits in two, forming two smaller nuclei such as krypton and barium, the weight of all fragments added together is less than that of the original uranium. The weight-loss turns into free energy...
Reluctant Clouds. In arid regions like New Mexico, Langmuir explained, big cumulus clouds often rise high in the air without dropping any rain. In such cases, the air does not contain enough natural nuclei (suitable dust particles) for moisture to condense upon. The warm air from over a sun-heated plain boils upward vigorously, but the moisture in it does not condense until the cold upper levels are reached. Then it condenses suddenly into very small ice particles that drift off at about 35,000 feet, leaving the ground dry, its inhabitants disappointed...
...milk rain from these reluctant clouds, said Langmuir, is to seed the air with particles of silver iodide, on which moisture condenses easily. When enough nuclei are present, snowflakes form on them at a comparatively low level. This condensation releases heat, which makes the air rise faster. The resulting turbulence tears the snowflakes apart. The fragments grow into larger flakes, releasing still more heat. The meteorological "chain reaction" turns the cloud into a violent thunderstorm that dashes torrents of rain on the ground below...