Prior to 1900 most meteorologists recognized that atmospheric temperature decreased with height and they assumed that this decrease was continuous. Late in the nineteenth century, however, the French meteorologist Leon Philippe Teisserenc de Bort used hydrogen balloons with precisely calibrated thermometers to demonstrate that while temperature did indeed decrease with height to approximately 8–12 km, above that height the temperature remained constant, or even increased slightly. Teisserenc de Bort referred to the atmosphere above 8–12 km as the “isothermal zone.” Later, studies by the German meteorologist Richard Assmann confirmed the observations of Teisserenc de Bort, and even extended them to note that the so-called “isothermal zone” was actually a zone with consistent temperature increase as a function of height. This condition of warmer air above cooler air is now referred to as an “inversion,” thus distinguishing it from the more commonly observed pattern of decreased temperature with height. In later writings, during the early twentieth century, Teisserenc de Bort postulated the existence of two atmospheric layers separated by the inversion – the troposphere, literally translated from the Greek word “tropein,” which means to turnover, and the stratosphere, literally translated from the Latin word “stratificationem,” which means to form into layers. Since his writings on this subject, the temperature inversion observed by Teisserenc de Bort has become known as the tropopause, the region separating the troposphere from the stratosphere. The discoveries of Teisserenc de Bort were not only important for our understanding of the physical arrangement of the atmosphere, but by focusing on atmospheric turnover in the troposphere, they laid the foundation for our current understanding of surface-atmosphere transport and even more general aspects of atmospheric physics.