THE CHEMICAL PHILOSOPHY OF THE ANCIENTS Speculations as to the origin and nature of matter, and as to the conditions and forces which affect it, are to be found, more or less imperfectly developed, in the oldest systems of philosophy of which we have any record. These speculations are not based, in any real sense, upon the systematic observation of natural phenomena. Still, as they appealed to human reason, they must be held to be founded upon experience, or at least not to be consciously inconsistent with it: All the oldest cosmogonies regarded water as the fundamental principle of things: from Okeanos sprang the gods—themselves deified personifications of the “elements” or principles of which the world was made. In the course of time this doctrine of the origin and essential nature of matter came to be more particularly associated with the name of Thales of Miletus, who lived six centuries before our era, and who, according to Tertullian, is to be regarded as the first of the race of the natural philosophers—that is, the first of those who made it their business to inquire after natural causes and phenomena. Thales is known to have passed some years of his life in Egypt, and to have been instructed in science by the priests of Thebes and Memphis; and it is therefore possible that he may have been influenced by the Egyptian teaching in the formulation of his cosmological theories. It is significant of the tenacity with which the mind clings to dogma and reveres authority that the teaching of Thales should have survived through the space of twenty-four centuries. It can be shown to have affected the course of chemical inquiry down to the close of the eighteenth century. It influenced the experimental labours of philosophers so diverse in character as Van Helmont, Boyle, Boerhaave, Priestley, and Lavoisier—all of whom made attempts to prove or disprove its adequacy. Van Helmont, indeed, was one of the most strenuous supporters of the doctrine of Thales, and sought to establish it by observations which, in the absence of all knowledge of the true nature of air and water, seemed at the time irrefutable. Perhaps the one most frequently cited is his observation on the growth of a plant which apparently had no other form of sustenance than water. He describes how he planted a willow weighing 5 lbs. in 200 lbs. of earth previously dried in an oven. The plant was regularly watered, when at the end of five years it was found to weigh 169 lbs. 3 oz., whereas the earth, after redrying, had lost only 2 oz. in weight. Hence, 164 lbs. of woody matter, leaves, roots, etc., had been produced seemingly from water alone. More than a century had to elapse before any clue to the true interpretation of Van Helmont’s experiment was gained. It was first furnished by the observations of Ingenhousz and Priestley.