Windswept_ The Story of Wind and Weather - Marq de Villiers [17]
It was, in fact, an early theory of everything, still the holy grail of science. It explained almost all the actions of nature. A fire, for example, was on earth merely impure ideal fire. When a pot was placed over a fire, the bottom of the pot became black; this happened because the real fire was a mixture of ideal fire and ideal earth, and therefore when the fire entered the pot to give it more of the property of hotness, some or all of the earth mixed with it was left behind as a soot. When sea water was heated, it absorbed the hotness of fire and moved away from water, becoming air; the impurity in real water, earth, then was left behind on the bottom of the pot as dry salt. And air, when cooled, would condense droplets of water, as when cold metal was placed in contact with the air above a kettle of boiling water or in moist air. This occurred because the property of coldness, taken from the metal or earth, moved the air toward wetness and therefore partially toward water.
Hmmm . . . it worked too. Mostly. But as a refinement, Aristotle, an honest skeptic, was obliged to add another element to the mix proposed by Empedocles. He called it quintaessentia, and the very name is a giveaway that he wasn't completely satisfied that the Big Four were a complete set. Quintaessentia was an eternal and unchangeable element otherwise known as ether, or space; it was the framework in which the other four existed, and it haunted physics until after 1850, when meticulous measurements finally made its retention impossible.
Aristotle also bought into the notion proposed by his master, Plato, that each of the four elements existed in a particular geometric form and the properties of the element were therefore related to that form. So fire particles were tetrahedrons, four-faced figures whose sharp points gave speed and burning sensations like arrows striking the flesh. Earth particles had the shapes of cubes, which accounted for their solidity; water particles had the smoother shape of twenty-sided icosahedrons, while those of air had the shape of an octahedron, a figure with eight sides. Ether, being the highest of the elements, had the most complex geometry, that of a pentagonal dodecahedron, a solid figure with twelve equal pentagonal faces. This was all wrong, of course, but not so wrong that its central notion, that each of the elements was made up of particles having a single definite shape, didn't resonate strongly with the modern theories of chemistry being developed in the seventeenth and eighteenth centuries.
The other prevailing Greek theory of the universe, and therefore of air, was the curiously modern-sounding theory of atoms. The first sighting of this interesting notion was in the writings of Leucippus, of whom otherwise nothing is known, and his student Democritus, somewhere around 400 B.C. They theorized, contrary to the four-elements school, that matter was not capable of infinite subdivision but contained ultimate and extremely small particles they called "atomus." These tiny particles, like matter, are eternal. Differences between substances are therefore due to the atoms of which they are composed, which are of different shapes and arrangements. Differences in the properties of substances, moreover, are not due to the atoms themselves but to the way in which they are arranged. The second point was that these atoms were in constant motion. The third was that they were separated by voids, or vacuums, in which they moved.
Aristotle disagreed vehemently with this whole idea of atoms. There was no such thing as a vacuum, he believed. Air has mass, yes— he showed that a container filled with air could not also be filled with water—but it couldn't possibly have weight; he flattened an airtight bag and weighed it, then filled it with