Rene Descartes (1596-1650), the philosopher, applied himself to the study of physics in all its branches, but especially to physiology. He said that science may be compared to a tree; metaphysics is the root, physics is the trunk, and the three chief branches are mechanics, medicine, and morals,—the three applications of our knowledge to the outward world, to the human body, and to the conduct of life.[876] He studied chemistry and anatomy, dissecting the heads of animals in order to explain imagination and memory, which he believed to be physical processes.[877] In 1629 he asks Mersenne to take care of himself, “till I find out if there is any means of getting a medical theory based on infallible demonstration, which is what I am now inquiring.”[878] Descartes embraced the doctrine of the circulation of the blood as discovered by Harvey, and he did much to popularise it, falling in as it did with his mechanical theory of life. He thought the nerves were tubular vessels which conduct the animal spirits to the muscles, and in their turn convey the impressions of the organs to the brain. He considered man and the animals were machines. “The animals act naturally and by springs, like a watch.”[879] “The greatest of all the prejudices we have retained from our infancy is that of believing that the beasts think.”[880] Naturally such a monstrous theory did much to encourage vivisection, a practice common with Descartes.[881] “The recluses of Port Royal,” says Dr. Wallace,[882] “seized it eagerly, discussed automatism, dissected living animals in order to show to a morbid curiosity the circulation of the blood, were careless of the cries of tortured dogs, and finally embalmed the doctrine in a syllogism of their logic: no matter thinks; every soul of beast is matter, therefore no soul of beast thinks. He held that the seat of the mind of man was in that structure of the brain called by anatomists the pineal gland.”
Malebranche (1638-1715) was a disciple of Descartes, who thought his system served to explain the mystery of life and thought. In his famous Recherche de la Verite he anticipated later discoveries in physiology, e.g., Hartley’s principle of the interdependence of vibrations in the nervous system and our conscious states.
Blaise Pascal (1623-1662), as a natural philosopher, rendered great services to science. The account of his experiments, written in 1662, on the equilibrium of fluids, entitles him to be considered one of the founders of hydrodynamics. His experiments on the pressure of the air and his invention for measuring it greatly assisted to advance the work begun by Galileo and Torricelli. Not only in the great work done, but in those which were undertaken in consequence of his inspiration, we recognise in Pascal one of the most brilliant scientists of a brilliant age.
Hobbes (1588-1679), the famous author of the Leviathan, endeavoured to base all that he could upon mathematical principles. Philosophy, he said, is concerned with the perfect knowledge of truth in all matters whatsoever. If the moral philosophers had done for mankind what the geometricians had effected, men would have enjoyed an immortal peace.
Benedict de Spinoza (1632-1677), the philosopher, had some medical training. His spirit has had a large share in moulding the philosophic thought of the nineteenth century. Novalis saw in him not an atheist, but a “God-intoxicated man.” His philosophy indeed was a pure pantheism; the foundation of his system is the doctrine of one infinite substance. All finite things are modes of this substance.
Sir Isaac Newton (1642-1727), the greatest of natural philosophers, in the years 1685 and 1686—years for ever to be remembered in the history of science—composed almost the whole of his famous work, the Principia.
Robert Boyle (1626-1691), one of the great nature philosophers of the seventeenth century, and one of the founders of the Royal Society, published his first book at Oxford, in 1660, entitled New Experiments, Physico-Mechanical, touching the Spring of Air, and its Effects. He was at one time deeply interested in alchemy. He was the first great investigator who carried out the suggestions of Bacon’s Novum Organon. He was a patient researcher and observer of facts.
Pierre Bayle (1647-1706), the author of the celebrated Historical and Critical Dictionary, was a sceptic, of a peculiar turn of mind. He knew so much concerning every side of every subject which he had considered, that he came to the conclusion that certainty was unattainable.
Van Helmont (1578-1644) was one of the most celebrated followers of Paracelsus. He learned astronomy, astrology, and philosophy at Rouvain, then studied magic under the Jesuits, and afterwards learned law, botany, and medicine; but he became disgusted with the pretensions of the latter science when it failed to cure him of the itch. He became a mystic, and attached himself to the principles of Tauler and Thomas à Kempis. Then he practised medicine as an act of charity, till, falling in with the works of Paracelsus, he devoted ten years to their study. He married, and devoted himself to medicine and chemistry, investigating the composition of the water of mineral springs. Few men have ever formed a nobler conception of the true physician than Van Helmont, or more earnestly endeavoured to live up to it. Notwithstanding his mysticism, science owes much to this philosopher, for he was an acute chemist. We owe to him the first application of the term “gas,” in the sense in which it is used at present. He discovered that gas is disengaged when heat is applied to various bodies, and when acids act upon metals and their carbonates. He discovered carbonic acid. He believed in the existence of an Archeus in man and animals, which is somewhat like the soul of man after the Fall; it resides in the stomach as creative thought, in the spleen as appetite. This Archeus is a ferment, and is the generative principle and basis of life. Disease is due to the Fall of Man. The Archeus influus causes general diseases; the Archei insiti, local diseases: dropsy, for example, is due to an obstruction of the passage of the kidney secretion by the enraged Archeus. Van Helmont gave wine in fevers, abhorred bleeding, and advocated the use of simple chemical medicines.
Francis de la Boë (Sylvius), (1614-1672) was a physician who founded the Medico-Chemical Sect amongst doctors. Health and disease he held to be due to the relations of the fluids of the body and their neutrality, diseases being caused by their acidity or alkalinity.