Knowing that I am an avid consumer of literature pertaining to time and astronomy, Melanie picked up a book at the library for me entitled, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, by Dava Sobel. When Christopher Columbus discovered America, his intended target was, if you recall, the Indies. His original charter was to find a direct westerly pathway from the Atlantic coast of Europe to the immensely profitable trade production region of the Indies as an alternative to to sailing around the treacherous Cape of Good Hope at the southern tip of Africa. How could such an experienced navigator have missed his mark by so far, you might reasonably ask? Didn't Columbus know how to use a sextant, or at least have a navigator who could?
The answer to the second question is, "no." The answer to the first question is complicated. Recall your elementary school poem titled In 1942, which began "In fourteen hundred ninety-two, Columbus sailed the ocean blue." John Hadley's and Thomas Godfrey's sextant - originally called an octant - was not invented and refined until the middle of the 18th century.
The answer to the first question is that prior to the advent of the sextant and accurate sea-going clocks, determining latitude was easy, but determining longitude was mostly guesswork and dead reckoning. Nobody in Columbus' day had a reliable means for computing longitude after more than a day or so at sea and out of sight of a known land mass.
As was (and still is) the case with many major scientific advances, the road to success was riddled with many technical, personal, and political obstacles. Prior to the last century, organized religions often were the most severe inhibitors of success - recall the Inquisition of Galileo for proclaiming a heliocentric universe. The pathway to discovering a means for determining longitude was strewn with all those forms of treachery.
Because so many ships - both commercial and military - were succumbing to perils of misadventure on the high seas, both England and France convened panels of mathematicians, sailors, astronomers, politicians, and clergy (what could go wrong?) to incentivize, judge, and reward efforts to solve "The Longitude Problem." England established its Board of Longitude in 1714, and France created its Bureau des Longitudes in 1795 (a bit late to the game). The grand reward for producing a reliable method for determining longitude within half a degree, known as the Longitude Prize, was £20,000 - or about £4.4M in 2019 money ($5.7M US).
Two competing, though in reality somewhat interdependent, methods were pitted against each other in the race for a solution - astronomical and chronological. The astronomical method which employed the sextant requires very accurate ephemerides of sun, moon, planet, and star positions. The chronological method requires a timekeeping apparatus that neither gains nor loses more than a few seconds per day while aboard a seafaring vessel being subject to wide variations in temperature, humidity, barometric pressure, a severe three-dimensional motion.
Astronomers and mathematicians worked tirelessly all over the known world observing and recording positions of heavenly objects - the moving planets ("planet" meaning "wanderer"), moon, sun, and the fixed stars. Johannes Kepler's derived laws of planetary motion and Isaac Newton's recent formulation of the laws of gravity play key roles in the ability to accumulate and publish yearly massive volumes of critical navigational data. Even so, very accurate reckoning of time was required to gain high accuracy in longitude determination. In fact, it could take a single navigator up to four hours to compute the longitude based on sextant readings.
The chronological longitude measuring method required precisely synchronized clocks based at the reference site at England's Royal Observatory - located on the declared prime meridian at Greenwich - and the remote location on a ship. Accordingly, the navigator would note the local time that a particular astronomical measurement was made (occultation of a star or Jovian moon by a planet or Earth's moon, a particular star observed at the zenith, etc.) and then compare it with the time the event would have occurred back "home" in Greenwich. Regardless of latitude, the earth rotates at a rate of once every 24 hours, so every hour of time difference equals 360/24 = 15 degrees of longitude, and every minute of time equals 1/4 of a degree of longitude.
Almost without a serious competitor, self-taught clockmaker John Harrison built four versions of his "sea clocks" over a period of forty years. He devised ingenious methods of "frictionless" bearings made of naturally oily woods, bimetal temperature-compensating pendulum components, winding mechanisms that did not halt clockworks movement during the winding process, and special construction of gears to eliminate cog mesh gaps, etc. His first model, which called "H-1," was a few feet of dimension on each side and weighted a few hundred pounds. By the time the H-4 was built - the model that finally won Harrison most of the Longitude Prize - Harrison was in his late sixties. It took the intervention of avid amateur astronomer King George III (the very same His Highness to whom the Declaration of Independence was delivered by the Continental Congress) to finally get Harrison his greatly deserved and hard-fought-for money.
Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time is a very worthwhile read for anyone interested in the history of clock making and timekeeping. Author Sobel tells an interesting tale of the catastrophic shipwrecks resulting from literally being lost at sea, thereby predicating the urgent need for precise longitude measurement, and of the sordid actions of bureaucrats and jealous men who sat in judgment and regulation of those who produce useful outcomes. It shows what determination and stick-to-itiveness can yield. Not every worthy endeavor results in eventual victory as did Harrison with his sea clocks, so it is nice to know that occasionally the good guy wins.
Surprisingly, there are no images published in the book. Here are detailed photographs of the H−1, H−2, H−3, and H−4 sea clocks.
Posted March 7, 2019