The thermal and chemical structure of the middle atmosphere is determined by molecules of air absorbing high-energy, solar, ultraviolet radiation. The dominant photochemical reaction for forming the stratosphere is dissociation of a molecule of oxygen into two atoms of oxygen. When a molecule is dissociated, the two pieces fly apart at high velocity. Temperature of air is directly proportional to the average velocity of all its molecules and atoms squared. Thus, photochemical dissociation converts bond energy efficiently and completely into air temperature. A molecule of oxygen is dissociated by absorbing ultraviolet-C radiation with frequencies around 1237 terahertz, energies around 5.1 electronvolts. Since oxygen makes up 20.95% of Earth’s atmosphere, there is ample oxygen to absorb all solar ultraviolet-C of appropriate frequencies that reaches the stratosphere, keeping the stratopause 30 to 40 oC warmer than the tropopause. Thus, the stratosphere forms an “electric” blanket warming Earth—electric in the sense that the thermal energy comes from a distant source, Sun, not from the body under the blanket, Earth. The second most important photochemical reaction in the stratosphere is dissociation of ozone by ultraviolet-B radiation with frequencies around 967 terahertz, energies around 4.0 electronvolts. While ozone concentrations, even in the ozone layer, are less than 10 parts per million, ozone is continually being formed and dissociated in the endless ozone-oxygen cycle, absorbing most solar ultraviolet-B radiation. When atoms of chlorine reach the lower stratosphere especially in winter, ozone concentrations that normally increase in winter can be depleted. One atom of chlorine, under the right conditions, can destroy 100,000 molecules of ozone. Depletion of the ozone layer allows more ultraviolet-B radiation than normal to reach Earth. Ultraviolet-B radiation is observed to cause sunburn, cataracts, skin cancer and mutations. It also dissociates ground-level ozone pollution, warming air in populated regions and penetrates oceans more than one hundred meters, very efficiently increasing ocean heat content as observed. Because of the ozone-oxygen cycle, where there are increased concentrations of ozone in the atmosphere, there is increased temperature. Sudden stratospheric warmings of 30-40 oC within days are typically associated with high concentrations of ozone and occur most frequently at altitudes of 30-50 km where dissociation of oxygen and ozone are most efficient. In 1798, Sir Benjamin Thompson proposed the mechanical theory of heat generated by friction when boring canon. This mechanical theory evolved into two fundamental assumptions: 1) heat is a flux of thermal energy measured in watts per square meter and 2) the greater the amount of flux absorbed, the hotter the body will become. Note that this approach never addresses the issue of what heat or thermal energy are, physically. (Complete abstract in poster file.)