Cosmos - Carl Sagan [78]
Huygens did much more. A key problem for marine navigation in this age was the determination of a longitude. Latitude could easily be determined by the stars—the farther south you were, the more southern constellations you could see. But longitude required precise timekeeping. An accurate shipboard clock would tell the time in your home port; the rising and setting of the Sun and stars would specify the local shipboard time; and the difference between the two would yield your longitude. Huygens invented the pendulum clock (its principle had been discovered earlier by Galileo), which was then employed, although not fully successfully, to calculate position in the midst of the great ocean. His efforts introduced an unprecedented accuracy in astronomical and other nautical clocks. He invented the spiral balance spring still used in some watches today; made fundamental contributions to mechanics—e.g., the calculation of centrifugal force—and, from a study of the game of dice, to the theory of probability. He improved the air pump, which was later to revolutionize the mining industry, and the “magic lantern,” the ancestor of the slide projector. He also invented something called the “gunpowder engine,” which influenced the development of another machine, the steam engine.
A detail from Christiaan Huygens’ Systema Saturnium, published in 1659. Shown is his (correct) explanation of the changing appearance of the rings of Saturn over the years as the relative geometry of Earth and Saturn changes. In position B the comparatively paper-thin rings disappear as they are seen edge-on. In position A they display their maximum extent visible from Earth, the configuration that caused Galileo, with a significantly inferior telescope, considerable consternation.
Huygens was delighted that the Copernican view of the Earth as a planet in motion around the Sun was widely accepted even by the ordinary people in Holland. Indeed, he said, Copernicus was acknowledged by all astronomers except those who “were a bit slow-witted or under the superstitions imposed by merely human authority.” In the Middle Ages, Christian philosophers were fond of arguing that, since the heavens circle the Earth once every day, they can hardly be infinite in extent; and therefore an infinite number of worlds, or even a large number of them (or even one other of them), is impossible. The discovery that the Earth is turning rather than the sky moving had important implications for the uniqueness of the Earth and the possiblity of life elsewhere. Copernicus held that not just the solar system but the entire universe was heliocentric, and Kepler denied that the stars have planetary systems. The first person to make explicit the idea of a large—indeed, an infinite—number of other worlds in orbit about other suns seems to have been Giordano Bruno. But others thought that the plurality of worlds followed immediately from the ideas of Copernicus and Kepler and found themselves aghast. In the early seventeenth century, Robert Merton contended that the heliocentric hypothesis implied a multitude of other planetary systems, and that this was an argument of the sort called reductio ad absurdum (Appendix 1), demonstrating the error of the initial assumption. He wrote, in an argument which may once have seemed withering,
For if the firmament be of such an incomparable bigness, as these Copernical giants will have it …, so vast and full of innumerable stars, as being