Timing swings with his pulse Galileo discovered a fundamental principle pendulums, which led to more accurate clocks and the ability to accurately measure longitude.
Pendulums
Have you ever been bored in Church? Kids fidget; adults gently doze. Most of us have done this at some time or another, but few have put such boredom to as good a use as Galileo, who made a fundamental scientific discovery that changed the world - much more productive than falling asleep.
While watching a chandelier swing back and forth at the Cathedral of Pisa in 1583, Galileo noticed something curious. We might expect a chandelier swinging farther to take longer, but not so. Galileo noticed that the time period to swing through one complete cycle is independent of the amplitude through which it swings. One can duplicate Galileo's pendulum experiments by timing a weight swinging on the end of a string. For not too large amplitudes, the time period for one complete cycle will be the same regardless of amplitude. The period does however depend on the length of the string. A longer pendulum will take longer to complete one cycle. For these experiments we would use a stopwatch, perhaps one built into most digital watches these days. But in Galileo's time, wristwatches were not yet available. He timed the swings with his pulse, the only timing device at hand.
Clocks
So what? Physicists might get excited over timing pendulum swings, but what relevance is it? The key historical detail here is simply that Galileo had to use his pulse as a timing device. Galileo's discovery finally allowed the construction of previously unavailable accurate clocks. The time period for a pendulum's swing depends on its easily to control length, and not on its hard to control amplitude. So, a pendulum is an excellent timing device for making clocks. That is why an old grandfather clock has a swinging pendulum and one can adjust its accuracy by moving the pendulum bob. It is less obvious, but watches also use a similar oscillating cycle. An older windup watch has a small oscillating spring. A newer watch has an oscillating quartz crystal. All of these are examples of the same principle, simple harmonic motion. So Galileo's chandelier observation paved the way for accurate clocks.
Navigation
But there's more. About a century earlier Columbus sailed west hoping to reach the east. Columbus thought he had reached the Indies, when in reality he had discovered the West (as opposed to the East) Indies and of course a new world. This great discovery was a colossal error caused mostly by the fifteenth century lack of knowledge of our world. But a less obvious culprit lurks in the shadows - poor navigation resulting not from ignorance or mistakes but from the limited tools available at the time. All the great seafarers of this era faced these navigational problems.
Prior to the global positioning system, navigators observed solar, lunar, and stellar positions to find their latitude and longitude. Latitude is easy. The altitude, in degrees, of Polaris above the northern horizon will equal the latitude. Columbus' contemporaries also used the altitude of the Sun at local noon corrected for the date.
Longitude
Longitude is harder. Prior to accurate clocks, lunar observations and very difficult calculations yielded approximate longitudes. Accurate longitudes with less difficult calculations require measured stellar positions and the time the observations were made. This reference time however must be the time at 0 degrees longitude (now Greenwich) rather than the local time. On a voyage extending months or years any error in the ship's clock will be compounded to the point that the navigator will have no idea what time it is at 0 degrees longitude and hence no idea of the ship's longitude. Observing the Sun at noon and resetting the clock can correct the local time, but resetting the longitude reference clock however requires returning to 0 degrees longitude. Hence without accurate clocks, early explorers could not determine their longitude. It took more than a century of refinement in clock design after Galileo's discovery, until John Harrison finally built a clock, in 1761, suitable for accurate marine navigation.
Seemingly simple impractical scientific discoveries often have far reaching consequences. Galileo's simple observations of cathedral lamps eventually led to accurate clocks that allowed explorers to more accurately measure longitudes and hence to explore and accurately map our world. Beats napping!
For more about Galileo go to:
Galileo's Telescope Discoveries
