Diagram showing the four elements, seasons and                                  body types, based on an edition of Isidore of                                  Seville’s Liber de Responsione Mundi (6th                                  or 7th century CE), Augsburg in 1472. Courtesy                                  Huntington Library.
 
 
                                                                                                                                           Elementary Knowledge
                                                                                                 May 31, 2010                                             
 
                                             A cornerstone of ancient Greek                                              science was the theory of the four                                              elements: Pythagoreans, Platonists,                                              Aristotelians and Stoics alike                                              subscribed to the idea that all                                              visible matter is formed of earth,                                              water, air and fire, varying only in                                              concentration and mode of                                              intermixture.The 'four                                              element theory' reached its standard                                              form when Empedocles of Acragas                                              (±492-432 BCE) synthesised earlier                                              attempts to identify the prima                                              materia, the primary or original                                              substance from which all else was                                              derived – historically as well as                                              chemically.
 
                                            During the formative period of Greek                                              philosophy, Thales of Miletus                                              (±624-547 BC) had argued that “the                                              beginning and end of the universe                                              was water”, while the Pythagorean                                              Hippasus of Metapontum (±500 BCE),                                              Heraclitus of Ephesus (±535-475 BCE)                                              and Zeno of Elea (±490-±430 BCE?)                                              all recognised fire as the first                                              principle. Other opinions were                                              voiced as well.
 
                                            The notion of the four classical                                              elements remained intact for                                              centuries and was used to account                                              for commonly observed physical                                              processes, including weather and                                              climate, as well as for cosmogonic                                              theories. The only significant                                              modification was Aristotle’s                                              treatment of the ‘fire’ constituting                                              stars and planets as a separate,                                              fifth element called ‘
aether’,                                              an innovation which only the                                              Aristotelians seem to have embraced.                                              As one follower put it: “The                                              substance of the heaven and the                                              stars we call aether … it is an                                              element different from the four                                              elements, pure and divine.” The idea                                              was that aethereal objects were                                              perfectly immutable, while ‘fiery’                                              ones were prone to change and decay.
 
                                            The theory fell out of favour with                                              the rise of modern chemistry in the                                              late 17th century. In 1669, the                                              German physician and alchemist,                                              Johann Joachim Becher, split the                                              element of earth into three,                                              corresponding to different degrees                                              of viscosity and fluidity. During                                              the same decade, the Irish                                              alchemist, Robert Boyle, while                                              pioneering chemical analysis,                                              theorised that the traditional                                              elements really were compounds and                                              mixtures, consisting of smaller                                              particles with a greater diversity.
 
                                            As the infant science of chemistry                                              progressed, the number of recognised                                              elements rose from 33 in 1789 and 49                                              in 1818 to the 66 that Dmitri                                              Mendeleyev incorporated in his                                              periodic table in 1869. This further                                              increased to the 118 elements that                                              have been observed up until now,                                              either in the laboratory, in space                                              or in nature.
 
                                            From this point of view, the ancient                                              Greek notion of ‘four elements’                                              sounds hopelessly obsolete, but is                                              it reasonable to view it as a                                              precursor to the modern chemical                                              definition of ‘elements’? Are                                              ancient and modern ‘elements’ really                                              the same thing? It is true that                                              Platonists associated each of the                                              four elements with one of the                                              regular polyhedra, so as to make                                              sense of their physical properties.                                              But were these philosophers really                                              so naïve as to imagine that all                                              known physical behaviour is                                              reducible to just four constituents?
 
                                            A recurrent topic in the classical                                              literature concerned the cycles                                              according to which one ‘element’                                              would transform into another. In the                                              modern sense of the word, elements                                              jumping positions in the periodic                                              table must be understood either in                                              terms of alchemy or of nuclear                                              chemistry, such as radioactive decay                                              or nuclear fusion. Yet it is clear                                              that this is not what Greek                                              philosophers were preoccupied with.                                              Heraclitus, for example, “called                                              change the upward and the downward                                              path, and held that the world comes                                              into being in virtue of this.
 
                                            When fire is condensed, it becomes                                              moist, and when compressed it turns                                              to water, water being congealed thus                                              turns to earth, and this he calls                                              the downward path. And, again, the                                              earth is in turn liquefied, and from                                              it water arises, and from that                                              everything else; for he refers                                              almost everything to the evaporation                                              from the sea. This is the path                                              upwards”. Clearly, speculations of                                              this type do not involve chemical                                              elements, but 
states of                                              aggregation.
 
                                            After the English natural                                              philosopher, Joseph Priestley                                              (1733-1804), successfully isolated                                              different ‘airs’ or gases, including                                              oxygen, three states of matter were                                              widely recognised – solids, liquids,                                              and gases. At a later date, one of                                              the most significant fall-outs of                                              the study of electromagnetism was                                              the recognition of a fourth state.                                              Its discoverer, the English                                              scientist, Michael Faraday                                              (1791-1867), dubbed it “radiant                                              matter”:
 
                                            “If now we conceive a change as far                                              beyond vaporisation as that is above                                              fluidity, and then take into account                                              also the proportional increased                                              extent of alteration as the changes                                              rise, we shall perhaps, if we can                                              form any conception at all, not fall                                              far short of radiant matter … The                                              simplicity of such a system is                                              singularly beautiful, the idea                                              grand, and worthy of Newton’s                                              approbation.”
 
                                            Sixty years later, it was Faraday’s                                              compatriot, Sir William Crookes                                              (1832-1919), who followed up in                                              earnest the suggestion of “Matter                                              classed into four states – solid,                                              liquid, gaseous, and radiant – which                                              depend upon differences in the                                              essential properties”. The term 
                                             plasma was employed for the                                              “radiant” or partly ionised gases by                                              the Nobel-prize winning American                                              chemist and physicist, Irving                                              Langmuir (1861-1957), in 1928.
 
                                            The discovery of the plasma state                                              allows a reappraisal of the ancient                                              theory of elements. If the four                                              ‘elements’ of the Greeks were really                                              states of matter, the concept is no                                              longer antiquated, but up to speed                                              with current understanding. If                                              ‘earth’ corresponds to solids,                                              ‘water’ to liquids, ‘air’ to gases,                                              and ‘fire’ to plasmas, the likes of                                              Empedocles effectively anticipated                                              Faraday by more than two millennia                                              with their insight that fire and                                              lightning represent an essentially                                              different regime of matter than                                              ordinary ‘air’. Faraday himself was                                              acutely aware of this connection:                                              “It was what the ancients believed,                                              and it may be what a future race                                              will realise.”
 
                                            With remarkable prescience, Crookes,                                              too, foresaw the immense scientific                                              potential of the ‘radiant’ state as                                              early as 1879:
 
                                            “In studying this Fourth state of                                              Matter we seem at length to have                                              within our grasp and obedient to our                                              control the little indivisible                                              particles which with good warrant                                              are supposed to constitute the                                              physical basis of the universe. … We                                              have actually touched the border                                              land where Matter and Force seem to                                              merge into one another, the shadowy                                              realm between Known and Unknown                                              which for me has always had peculiar                                              temptations. I venture to think that                                              the greatest scientific problems of                                              the future will find their solution                                              in this Border Land, and even beyond                                              …”
 
                                            Those at the forefront of plasma                                              science today would agree that                                              plasma constitutes “the physical                                              basis of the universe” and that it                                              can potentially solve “the greatest                                              scientific problems”. Indeed, owing                                              to its ubiquity in space, plasma has                                              been promoted from being the                                              ‘fourth’ state to the fundamental                                              state of matter. And this, again,                                              accords quite well with Heraclitus’                                              hoary adage: T
à dè pánta oiakízei                                              keraunós – ‘Thunderbolt steers                                              all things’.
 
                                            Contributed by Rens Van Der Sluijs