Boyle was the first to formulate our present conception of an element in contradistinction to that of the Greeks and the schoolmen who influenced the theories of the iatro-chemists. In the sense understood by him, the Aristotelian elements were not true elements, nor were the salt, sulphur, and mercury of the school of Paracelsus. He was also the first to define the relation of an element to a compound, and to draw the distinction we still make between compounds and mixtures. He revived the atomic hypothesis, and explained chemical combination on the basis of affinity. He contended that one of the main objects of the chemist was to ascertain the nature of compounds; and thereby he stimulated the application of analysis to chemistry. Boyle discovered a number of qualitative reactions, and applied them to the detection of substances, either free or in combination. But Boyle’s greatest service to learning consisted in the new spirit he introduced into chemistry. Henceforward chemistry was no longer the mere helpmeet of medicine. She became an independent science, the principles of which were to be ascertained by experiment; a science to be studied with the object of discovering the laws regulating the phenomena with which it is concerned—and hence elucidating truth for truth’s sake. The old philosophy of the Greeks had, as we have seen, become merged into the doctrine of the iatro-chemists; and this was now to be purified from the theosophical mysticism with which Paracelsus and his followers had enshrouded it. “The dialectical subtleties of the schoolmen much more,” says Boyle, “declare the wit of him that uses them than increase the knowledge or remove the doubts of sober lovers of truth.... For in such speculative inquiries where the naked knowledge of the truth is the thing principally aimed at, what does he teach me worth thanks, that does not, if he can, make his notion intelligible to me, but by mystical terms and ambiguous phrases darkens what he should clear up, and makes me add the trouble of guessing at the sense of what he equivocally expresses, to that of learning the truth of what he seems to deliver.” The influence of the new spirit thus infused into the science by Boyle is seen in the general style of chemical literature at the end of the seventeenth century, when compared with that of the close of the sixteenth. The mysticism and obscurity of the alchemists were no longer tolerated. Boyle was slender and tall, with a countenance pale and emaciated. His constitution was delicate and his body feeble, and it was only by strict attention to diet and regularity of exercise that he accomplished what he did. Although he suffered occasionally from an excessive lowness of spirits, there was nothing morose or ascetic in his nature. He was never married, although, says his friend John Evelyn, “few men were more facetious and agreeable in conversation with the ladies whenever he happened to be engaged among them.”