Only less important than that of mechanics was the development of biology in the seventeenth century. William Harvey, supported by the excellent work of anatomists that had begun with Vesalius, but held back by many vestiges of the old superstitious belief in authority and the garbled teachings of Hippocrates and Galen, in the early years of the century discovered the circulation of the blood.〖H. C., xxxviii, 62ff.〗 After long and most admirable investigations and self-criticism, in the year 1628 he gave this discovery to the world.

It is impossible to imagine a more illuminating contrast between the false learning of the Middle Ages and the sound positive knowledge of modern times than is presented in Harvey’s book. For at almost every point the work of Harvey himself has quite as much the modern flavor as that of Newton. The introduction presents the old traditional views on the physiological functions of heart and lungs, and bewilders with its meaningless play with words. There follow upon this the simplest descriptions of observations and experiments, and the soundest reasoning from such positive knowledge, till one feels that he has passed from a dream into reality.

The work of Harvey, like so much of the work of great Englishmen, was isolated, and the full development of biology came somewhat later, in mid-century and thereafter. In this later growth, aided by the microscope and the principles of mechanics, the studies of Swammerdam, Grew, Malpighi, Redi, Borelli, Leeuwenhoek, and others, provided many important data in the most widely different departments of biology. But natural history lacked the great foundation of accurate descriptive knowledge, arranged in order, that astronomy possessed, and, as a result much of the great work which the biological renaissance began was interrupted for a century. Among the feats of seventeenth-century biology were microscopical studies of the anatomy of both plants and animals (Nehemiah Grew, Malpighi, Leeuwenhoek), the beginnings of embryology (Harvey, Swammerdam), mechanical physiology (Borelli) including recognition of the nature of reflex action by Descartes, experimental studies tending to overthrow belief in spontaneous generation (Redi), and even observations on the physiological action of poisons.

In this century, in spite of the admirable work of Robert Boyle, somewhat overestimated in his own day however, chemistry languished under the sway of a false theory. Similarly, heat, electricity, and magnetism were of no great importance, unless the magistral work on magnetism of William Gilbert, physician to Queen Elizabeth, published in 1600, be reckoned.

Two other departments of physical science, however, the study of atmospheric pressure and optics, were more fortunate. Torricelli and Viviani, pupils of Galileo, Otto von Guericke, Pascal, and Boyle investigated the barometer and the pressure of gases and worked up the fundamental conclusions. Optics was investigated by no less men than Newton and Huygens, and at their hands underwent a wonderful practical transformation. But this subject requires a peculiarly subtle theoretical foundation, and the times were not yet ripe even for a Newton to enter the true path of theoretical speculation.

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