Galileo, as every one knows, was condemned by the Inquisition, first privately in 1616, and then publicly in 1633, on which latter occasion he recanted, and promised never again to maintain that the earth rotates or revolves. The Inquisition was successful in putting an end to science in Italy, which did not revive there for centuries. But it failed to prevent men of science from adopting the heliocentric theory, and did considerable damage to the Church by its stupidity. Fortunately there were Protestant countries, where the clergy, however anxious to do harm to science, were unable to gain control of the State.
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Newton ( 1647-1727) achieved the final and complete triumph for which Copernicus, Kepler, and Galileo had prepared the way. Starting from his three laws of motion–of which the first two are due to Galileo–he proved that Kepler’s three laws are equivalent to the proposition that every planet, at every moment, has an acceleration towards the sun which varies inversely as the square of the distance from the sun. He showed that accelerations towards the earth and the sun, following the same formula, explain the moon’s motion, and that the acceleration of falling bodies on the earth’s surface is again related to that of the moon according to the inverse square law. He defined “force” as the cause of change of motion, i.e., of acceleration. He was thus able to enunciate his law of universal gravitation: “Every body attracts every other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.” From this formula he was able to deduce everything in planetary theory: the motions of the planets and their satellites, the orbits of comets, the tides. It appeared later that even the minute departures from elliptical orbits on the part of the planets were deducible from Newton’s law. The triumph was so complete that Newton was in danger of becoming another Aristotle, and imposing an insuperable barrier to progress. In England, it was not till a century after his death that men freed themselves from his authority sufficiently to do important original work in the subjects of which he had treated.
The seventeenth century was remarkable, not only in astronomy and dynamics, but in many other ways connected with science.
Take first the question of scientific instruments. * The compound microscope was invented just before the seventeenth century, about 1590. The telescope was invented in 1608, by a Dutchman named Lippershey, though it was Galileo who first made serious use of it for scientific purposes. Galileo also invented the thermometer–at least, this seems most probable. His pupil Torricelli invented the barometer. Guericke ( 1602-86) invented the air pump. Clocks, though not new, were greatly improved in the seventeenth century, largely by the work of Galileo. Owing to these inventions, scientific observa-
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* On this subject, see the chapter “Scientific Instruments” in A History of Science, Technology, and Philosophy in the Sixteenth and Seventeenth Centuries, by A. Wolf.
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tion became immensely more exact and more extensive than it had been at any former time.
Next, there was important work in other sciences than astronomy and dynamics. Gilbert ( 1540-1603) published his great book on the magnet in 1600. Harvey ( 1578-1657) discovered the circulation of the blood, and published his discovery in 1628. Leeuwenhoek ( 16321723) discovered spermatozoa, though another man, Stephen Hamm, had discovered them, apparently, a few months earlier; Leeuwenhoek also discovered protozoa or unicellular organisms, and even bacteria. Robert Boyle ( 1627-91) was, as children were taught when I was young, “the father of chemistry and son of the Earl of Cork”; he is now chiefly remembered on account of “Boyle’s Law,” that in a given quantity of gas at a given temperature, pressure is inversely proportional to volume.
I have hitherto said nothing of the advances in pure mathematics, but these were very great indeed, and were indispensable to much of the work in the physical sciences. Napier published his invention of logarithms in 1614. Co-ordinate geometry resulted from the work of several seventeenth-century mathematicians, among whom the greatest contribution was made by Descartes. The differential and integral calculus was invented independently by Newton and Leibniz; it is the instrument for almost all higher mathematics. These are only the most outstanding achievements in pure mathematics; there were innumerable others of great importance.
The consequence of the scientific work we have been considering was that the outlook of educated men was completely transformed. At the beginning of the century, Sir Thomas Browne took part in trials for witchcraft; at the end, such a thing would have been impossible. In Shakespeare’s time, comets were still portents; after the publication of Newton Principia in 1687, it was known that he and Halley had calculated the orbits of certain comets, and that they were as obedient as the planets to the law of gravitation. The reign of law had established its hold on men’s imaginations, making such things as magic and sorcery incredible. In 1700 the mental outlook of educated men was completely modern; in 1600, except among a very few, it was still largely medieval.
In the remainder of this chapter I shall try to state briefly the philosophical beliefs which appeared to follow from seventeenth
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century science, and some of the respects in which modern science differs from that of Newton.
The first thing to note is the removal of almost all traces of animism from the laws of physics. The Greeks, though they did not say so explicitly, evidently considered the power of movement a sign of life. To common-sense observation it seems that animals move themselves, while dead matter only moves when impelled by an external force. The soul of an animal, in Aristotle, has various functions, and one of them is to move the animal’s body. The sun and planets, in Greek thinking, are apt to be gods, or at least regulated and moved by gods. Anaxagoras thought otherwise, but was impious. Democritus thought otherwise, but was neglected, except by the Epicureans, in favour of Plato and Aristotle. Aristotle’s forty-seven or fifty-five unmoved movers are divine spirits, and are the ultimate source of all the motion in the universe. Left to itself, any inanimate body would soon become motionless; thus the operation of soul on matter has to be continuous if motion is not to cease.
All this was changed by the first law of motion. Lifeless matter, once set moving, will continue to move for ever unless stopped by some external cause. Moreover the external causes of change of motion turned out to be themselves material, whenever they could be definitely ascertained. The solar system, at any rate, was kept going by its own momentum and its own laws; no outside interference was needed. There might still seem to be need of God to set the mechanism working; the planets, according to Newton, were originally hurled by the hand of God. But when He had done this, and decreed the law of gravitation, everything went on by itself without further need of divine intervention. When Laplace suggested that the same forces which are now operative might have caused the planets to grow out of the sun, God’s share in the course of nature was pushed still further back. He might remain as Creator, but even that was doubtful, since it was not clear that the world had a beginning in time. Although most of the men of science were models of piety, the outlook suggested by their work was disturbing to orthodoxy, and the theologians were quite justified in feeling uneasy.
Another thing that resulted from science was a profound change in the conception of man’s place in the universe. In the medieval world, the earth was the centre of the heavens, and everything had a purpose
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concerned with man. In the Newtonian world, the earth was a minor planet of a not specially distinguished star; astronomical distances were so vast that the earth, in comparison, was a mere pin-point. It seemed unlikely that this immense apparatus was all designed for the good of certain small creatures on this pin-point. Moreover purpose, which had since Aristotle formed an intimate part of the conception of science, was now thrust out of scientific procedure. Any one might still believe that the heavens exist to declare the glory of God, but no one could let this belief intervene in an astronomical calculation. The world might have a purpose, but purposes could no longer enter into scientific explanations.
The Copernican theory should have been humbling to human pride, but in fact the contrary effect was produced, for the triumphs of science revived human pride. The dying ancient world had been obsessed with a sense of sin, and had bequeathed this as an oppression to the Middle Ages. To be humble before God was both right and prudent, for God would punish pride. Pestilences, floods, earthquakes, Turks, Tartars, and comets perplexed the gloomy centuries, and it was felt that only greater and greater humility would avert these real or threatened calamities. But it became impossible to remain humble when men were achieving such triumphs:
Nature and Nature’s laws lay hid in night.
