Windswept_ The Story of Wind and Weather - Marq de Villiers [18]
Philo of Byzantium, in the third century B.C. performed a more sophisticated version of Aristotle's mass experiment, and was thus the first to really prove that air had substance. He attached a tube to a glass globe, then inserted the open end of the tube into a dish of water. When he placed the globe in shadow, the water rose within the tube. When he exposed the globe to sunlight, the level fell. "The same effect," he wrote, "is produced if one heats the globe with fire."
He had—though he didn't know it—stumbled on the true cause of wind.5 He was the first meteorologist.
IV
And there the science of air rested, for another two thousand years or so. Inquiry into the physical world went on, but at a desultory pace, and philosophers turned their attention to other matters, such as the transmutation of base metals into gold, and to increasingly odd notions of cosmology; alchemy and astrology dominated the physical sciences until the Middle Ages. The first comprehensive theory after Aristotle's that sought to explain air and combustion wasn't formulated until the late seventeenth century. This phlogiston theory was entirely plausible in the light of current knowledge, though it, too, was entirely wrong. Its ascendancy lasted about one hundred years, and when it was finally put to rest, the way was opened for the birth of a modern, measurement-based, technologically oriented, practical discipline that we now know as atmospheric science, of which meteorology is an important part.
The theory was German in origin, and the two scientists most identified with it were Johann Joachim Becher and Georg Ernst Stahl, who first used the word phlogiston in 1700. Following the ancient Greek codification practice, the theory sought to reduce everything to three essences that make up all matter: sulfa, or terra pinguis, the essence of inflammability; mercury, or terra mercurialis, the essence of fluidity; and salt, or terra lapida. Terra pinguis was later renamed phlogiston. Under the pressure of the church, living matter was excluded from this taxonomy, because of course it contained the potential for a soul that differed in composition from nonliving matter, and since it was divinely inspired, was necessarily outside earthly classification. This was Stahl's vitalism theory, outlined in his The True Theory of Medicine.
The governing idea of phlogiston was that all metals were made of a calx, or residue, combined with phlogiston, the fiery principle, which was liberated during combustion, leaving only the calx. Air, according to this theory, was merely a receptacle for phlogiston. Combustibles, or calcinable substances, were not elements at all, but merely compounds containing phlogiston. For example, rusting iron was believed to be losing its phlogiston and thereby returning to its elemental state.
Similarly, flames extinguish because the air becomes saturated with phlogiston. Charcoal leaves little residue after burning because it is nearly pure phlogiston. Mice die in confined spaces because the air becomes saturated with phlogiston.
The theory had many advantages. It explained, for example, how air at first supports combustion and then after a while does not. It also addressed some of the obvious drawbacks of Aristotle's theory, particularly his hazy notions of chemical change. But phlogiston nevertheless came under increasing attack. At first, the results of hundreds of practical experiments in dozens of laboratories around Europe were shoehorned into the theory, but too many just didn't seem to fit. Why, for example, did some metals, such as magnesium, actually gain mass when burned? Phlogistonists finessed the discrepancy by assigning phlogiston a negative mass, or by asserting that air entered the metal to fill the vacuum after phlogiston left, but this satisfied hardly anyone.
Even Joseph Priestley, the towering and cantankerous intellect who discovered the existence