A major role in the cultivation of a new scientific attitude was taken by the English thinker and politician Francis Bacon. Though not himself a successful practitioner of science, Bacon was a tireless proponent of the need to observe and to accumulate data. In Novum Organum (1620) he wrote that scientists must think all things possible until all things could be tested. By relying on “the empirical faculty,” which learns from experience, Bacon was promoting what he called induction, which proceeds from the particular observed phenomenon to the general conclusion to be drawn.
By contrast, deduction, the medieval mode of reasoning still in fashion in Bacon’s day, proceeds from the general expectation to the particular example as proof. Deduction is not necessarily antiscientific, for it sometimes produces the guesses that advance theoretical science. What Bacon particularly attacked was the inclination of deductive reason to accept general opinions as “settled and immovable.” Ranking high among such established opinions were the views of the universe associated with two authorities of antiquity, Aristotle and Ptolemy. Bacon’s contemporary, Galileo Galilei (1564-1642), ridiculed blind acceptance of ancient authorities and thereby became embroiled with the church.
Galileo was also one of many who contributed to the invention of new instruments that permitted the more exact measurements and more detailed observations needed by inductive science. It is probable, for example, that Dutch glassmakers first put two lenses together and discovered that they could thus obtain greater magnification; by 1610 Galileo was using the new device in the form of a telescope to study the heavens.
Later in the century two Dutchmen employed it in the form of a microscope—Jan Swammerdam (1637-1680) to analyze blood (he probably discovered red corpuscles), and Anthony Van Leeuwenhoek (1632-1723) to view and describe protozoa and bacteria. Working from the experiments of Galileo, other technicians developed such instruments of measurement as the thermometer and the barometer. Using the barometer, the French mathematician Blaise Pascal (1623-1662) proved that air pressure diminished with altitude; for this he went on to counter the old adage attributed to Rabelais, “Nature abhors a vacuum,” by showing that a vacuum is possible.
King Charles II of England roared with laughter on being told that members of his Royal Society were weighing the air. Yet the Royal Society for Improving Natural Knowledge, founded in 1662, and its French counterpart, the Academie des Sciences (1666), were important promoters of scientific investigation. An international scientific community arose through the formal exchanges of the corresponding secretaries and the publications of such academies, and also through the extensive private correspondence among members and their acquaintances.
Both professionals and aristocrats joined learned societies, and many a gentleman and an occasional lady worked in a private laboratory or observatory. One gentleman, Robert Boyle (1627-1691), son of an Irish earl, discovered the law of physics named after him—that under compression the volume of a gas is inversely proportional to the amount of pressure. The publication of scientific discoveries helped bridge the gap between theory and practice, for it showed scientists where their work related to that of others and helped indicate which problems most needed attention.
Meantime, the basic language of science—mathematices—was taking a great leap forward. In 155 Simon Stevin (1548-1620), a Fleming, published The Decimal, Teaching with Unheard-of Ease How to Perform All Calculations Necessary among Men by Whole Numbers without Fractions. Another great timesaver was devised by the Scot John Napier (1550-1617) with his Marvelous Rule of Logarithms (1616), which shortened the laborious processes of multiplying, dividing, and finding square roots. Rene Descartes (1596-1650) worked out analytical geometry.
The mathematical achievements of the century culminated in a method for dealing with variables and probabilities. Pascal made a beginning with studies of games of chance, and Dutch insurance actuaries devised tables to estimate the life expectancy of their clients. The Englishman Sir Isaac Newton (1642-1727) and the German baron Gottfried Wilhelm von Leibniz (1646-1716) invented calculus, apparently quite independently of each other. Without Cartesian geometry and calculus, Newton could never have made the calculations supporting his revolutionary hypotheses in astronomy and physics.
In astronomy the heliocentric theory advanced by Copernicus in the sixteenth century proved to be only a beginning. It raised many difficulties, notably when observation of planetary orbits did not confirm Copernicus’s belief that the planets revolved about the sun in circular paths. The German Johannes Kepler (1571-1630) proved mathematically that the orbits were in fact elliptical. Then Galileo’s telescope revealed the existence of spots on the sun, rings around Saturn, and moonlike satellites around Jupiter. All this evidence led Galileo to publish a book in 1632 defending the heliocentric concept and ridiculing supporters of the traditional geocentric (earth-centered) theory. But the church brought Galileo before the Inquisition, which placed his book on the Index of prohibited works and sentenced him to perpetual house arrest.
A celebrated story recounts Galileo’s experiment of dropping balls of different weights from the Leaning Tower of Pisa to test Aristotle’s theory that objects fall at velocities proportional to their weight. While the story itself may not be true, Galileo did disprove Aristotle. Despite the tendency toward self-promotion, Galileo’s studies of projectiles, pendulums, and falling and rolling bodies helped establish modern ideas of acceleration and inertia, which Newton later formulated mathematically.
In 1687 Newton published the laws of motion together with other great discoveries in Philosophiae Naturalis Principi a Mathematica (Mathematical Principles of Natural Philosophy). He had made many of these findings two decades earlier, when he was still an undergraduate at Cambridge; he was recognized in his later years, gaining a professorship at Cambridge, a knighthood, the presidency of the Royal Society, and the well- paid post of Master of the Mint. But Newton’s greatest contribution was the law of gravitation.
It followed from his laws of motion, which picture bodies moving in response to forces acting upon them. These forces are at work in the mutual attraction of the sun, the planets, and their satellites, which are thereby held in their orbits. Newton also promoted the development of optics by using a prism to separate sunlight into the colors of the spectrum. He demonstrated that color is not intrinsic to an object but the result of reflection and absorption of light.
Meanwhile, the mechanistic views of the physicists were invading geology and physiology. In 1600 the English physician William Gilbert (1540-1603) suggested that the earth itself was a giant magnet. In 1628 William Harvey (1578-1657) published his demonstration that the human heart is a pump driving the blood around the body through a single circulatory system. Harvey’s theory, confirmed a generation later through microscopic observation discredited the hypothesis handed down from Galen that the blood in the arteries moved quite separately from that in the veins. And in 1679 the Italian anatomist Alphonso Borelli (1608-1679) showed that the human arm is a lever and that muscles do mechanical work.