are modified, and transformation is possible. This determinist conception was afterward mingled in the minds of the alchemists with Oriental mysticism; but it must be remarked that it presented, in the Greek philosophers Thales, Anaximenes, Heraclitus, Empedocles, Plato, and their immediate heirs, a really scientific character. Michael Psellus was faithful to their doctrine when he wrote to the Patriarch Xiphilin, in a letter which was used as the Preface to the Collection of the Greek Alchemists: "The changes of nature are made naturally, not by virtue of an incantation or a miracle, or of a secret formula. There is an art of transmutation. . . . You want me to teach you the art that resides in fire and furnaces, and which produces the destruction of substances and the transmutation of their natures. Some believe that this is a secret knowledge, gained by initiation, which they have not tried to reduce to a rational form; which seems to me an enormous error. For myself, I try first to learn the causes, and to deduce from them a rational explanation of the facts. I sought it in the nature of the four elements, from which everything comes by combination, and to which everything returns by solution."
From Greece alchemy then received, with the idea of a primary matter and the system of atoms, a whole contingent of rationalistic notions which subsequently modified more or less Christian mysticism and the traditions of the East. The effort of the alchemists of the middle ages to divest the metals of their individual qualities in order to reach the primitive matter, the mercury of the old philosophers, was then in harmony with Plato's metaphysics. But, in the operations they performed for that end, they could only determine the indefinite transformation of the elements, and they represented the mysterious process under the symbolical form of a ring-serpent which has neither beginning nor end. This hopeless picture of chemistry did not cease to be true till the end of the last century. By introducing the balance into laboratories, Lavoisier demonstrated that the weight of metals is invariable, and, in a general way, that the origin of all chemical phenomena lies in the reactions of a small number of undecomposable bodies, the weight and properties of which are constant.
This great discovery sapped the alchemic doctrine of the transmutation at its very foundations. It is, however, still permissible to ask if the present elements, as yet undecomposed, are really simple bodies. If Prout's hypothesis that they are polymers of hydrogen could be demonstrated, the hope of passing from one to the other would be entirely legitimate. But the recently carefully made determinations of the equivalents of simple bodies by Dumas and Stas have weakened that theory. The laws of specific