That water might be converted by fire into air was surmised from the earliest times. Such a supposition naturally sprung from the circumstance that water was everywhere recognised to disappear or to pass into the air under the influence of fire or solar heat. The supposition had grown into a fixed belief in the Middle Ages.
Even Priestley, as late as the end of the eighteenth century, imagined for a time that he had obtained proof of such a mutual conversion. The possibility of the transmutation of water into earth was a belief current through twenty centuries, and was only definitely and finally disproved by Lavoisier in 1770. The conception of fire as the primal principle has its germ in the fire- or sun-worship of the Chaldeans, Scythians, Persians, Parsees, and Hindus, and it is not difficult to trace, therefore, how heat came to be regarded either as antecedent to, or as associated with, the other primal principles. Empedokles, apparently, was the first whose name has come down to us to reintroduce the definite conception of four primal elements—fire, air, water, and earth. These he regarded as distinct, and incapable of being transmuted, but as forming all varieties of matter by intermixture in various proportions. These principles he deified, Zeus being the personification of the element of fire, Here of air, Nestis of water, and Aidoneous of earth.
