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Time and Travel

by Peggy M. Baker, Director & Librarian,
Pilgrim Society & Pilgrim Hall Museum

Modern navigators accept without wonder tools that would have been inconceivable to earlier generations. How would you explain GPS (Global Positioning System) to Captain Christopher Jones of the Mayflower ? Would he have understood – or even believed in the possibility of – a small electronic device that receives data on the relative position of dozens of satellites, uses signals that are transmitted from these satellites to chart the precise time (via an atomic clock), performs innumerable mathematical equations almost instantaneously and – voila! - determines the precise location of a vessel?

Imagine, now, that the year is 1620. There is no Global Positioning System. How would YOU determine the position of the
Mayflower at sea? And, without knowing where the Mayflower was located, would you be able to bring her safely to shore?

The Mayflower had no electronic devices or satellites or atomic clocks. It was not, however, entirely “at sea.”

Many navigational tools - all aimed at identifying a ship’s current position – had been developed over the centuries. By modern standards, they were crude and unreliable. These navigational tools, however, enabled the skillful and intrepid mariners of the 17th century to explore the Atlantic, to discover new continents, to establish and maintain communication with colonies in these new lands.

The most basic of these navigational tools can still be found in a modern sporting goods store.

The magnetic compass began as a simple needle that pointed north when floated in a bowl of water. By 1620, the free-floating “compass rose” card (showing 32 points of the compass with a fleur-de-lis for the North), with the needle glued to the underside of the card, was common. The compass would be suspended by gimbals (which allow the compass to remain horizontal even if the ship is not!) in a wooden box and covered with glass for protection from the elements. An experienced navigator, observing winds and tides, and logging course and speed, could use a compass to estimate a rough position at sea.

The compass contained within this wooden box dates from around 1850 but in design, in construction and in use it varies little from the compass that would have been used aboard the Mayflower.    

This process was known as “dead reckoning.” During each 4-hour “watch,” the navigator would use a traverse board to track, in half-hour intervals or “bells,” two very important pieces of information: in what compass direction had the vessel traveled and at what speed.

The traverse board was a flat board, approximately 12” tall by 8” wide, with a compass rose painted on it. The rose was encircled by 8 rows of holes corresponding to the 32 directional points of the compass (256 holes in all). Beneath the compass rose and its 8 rows of encircling holes, was another set of 8 straight rows of holes, 8 or 9 across (between 64 and 72 holes in all).

The 256 encircling holes were used to record direction. At the end of each “bell” (measured by a half-hour sandglass), the navigator would note the vessel’s compass direction. A peg was then put in the first circle of holes at the directional point toward which the compass had been pointed during that first half hour. A second peg was put in the second circle of holes at the next “bell” to record the direction the compass had been pointed during that second half hour, and so on for each half hour during the watch.

The 8 straight rows of holes below the compass rose were used to chart the speed of the ship. The crew would estimate the speed of the ship by dropping a “chip log” (a special board attached to a long “log line”) over the stern and letting it pull out the log line for a minute’s time, as measured by another sandglass. The log line had a series of knots tied in it; each knot that was paid out marked a (nautical) mile per hour. When the speed was ascertained at the end of the first bell, a peg was put in the appropriate hole in the first row (using, for example, the 4th hole in the row to indicate 4 knots) and so on for each bell in the watch.

At the end of the 4-hour watch, there were 8 directional pegs and 8 speed pegs in the traverse board. The navigator used this information to chart the ship’s progress on a sea chart. He then made a straight line from the position at the end of the previous watch to show how far along the desired course the ship had gone.

Astronomy was also used in the service of navigation. The north-south global position (latitude) of a ship can be determined by the altitude of the North Star (or, in the southern hemisphere, the altitude of the sun) above the horizon. By 1620, the development of tools such as quadrants, astrolabes, cross-staffs and back-staffs had made it possible to use the position of stars and planets to determine latitude to a fair degree of accuracy.

It is not, however, possible to use celestial navigation to determine the east-west global position (longitude) of a ship.

This was not a severe impediment to early Atlantic exploration and trade. Ships regularly and reliably found their way between the Americas and Europe. As commerce increased, however, it became apparent that incomplete navigational knowledge lengthened voyages and created an adverse effect on revenues.

Philip II of Spain, relying for income on the “Treasure Ships” sailing from America, was the first to offer a prize for solving the problem of longitude at sea. The great Galileo was able to calculate longitude by using his new and powerful astronomical telescope to identify and track the regular eclipses of the planet Jupiter. This was a great advance in knowledge and proved useful for improving land maps. It did not, however, help navigation. Conditions at sea simply did not allow aiming and focusing an extremely large and expensive telescope at very tiny objects in the sky!

The search for a method of determining longitude turned to timekeeping.

The earth takes 24 hours to rotate, or to go 360 degrees east-west. The earth rotates one degree every four minutes, or fifteen degrees every hour. Therefore, longitude (the measure of global positioning east-west) can be seen in terms of time - the difference between the time at the actual location of the ship and the time at a point of reference, or a “meridian.” This time can, in principle, be measured by a clock. An actual clock, carried on board ship, could theoretically be maintained at the time of the reference meridian (what we know as Greenwich time). Local time could be ascertained by the position of the sun at 12:00 o’clock noon. The difference between the two times would enable the navigator to determine longitude – IF and ONLY IF the clock set at the reference meridian is almost completely accurate. The accuracy is the problem! In order to give a useful position after a ship has been at sea for weeks and weeks, a clock has to be proven to be reliably accurate to within seconds a day for months at a time amid variations of temperature, humidity and the motions of the sea.

In 1620, the technology did not exist to make that degree of accuracy possible. Clocks (weight-driven timekeepers) were unreliable – and watches (spring-driven timekeepers) were even worse!

It took 150 years after the voyage of the Mayflower for such a timepiece to be invented.

The intense 17th century interest in science and technology led to great improvements in timekeeping. By 1660, clocks had been developed that could keep time to within seconds a day. These clocks were, however, weight-driven tall case clocks with long pendulums – totally unsuited for life at sea. Sir Isaac Newton listed the difficulties of using clocks at sea as “the Motion of Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes.”

Charles II founded the Royal Observatory at Greenwich in 1674 specifically to improve navigation at sea and to solve the problem of longitude. It was recognized by now that solving the problem of ascertaining longitude depended on accurate measurement of time.

This was a problem that was becoming ever more critical. Shipping and the volume of ocean trade had grown; international competition had become stiffer and often violent. New sea routes needed to be found to protect heavily loaded vessels from pirates and privateers. As very lengthy Pacific voyages became more common, more men and ships were lost to disease and lack of supplies – it became harder to recruit sailors and investors alike!

In 1707, an English fleet under the command of Admiral Sir Clowdisley Shovel was wrecked in fog off the Scilly Isles. The admiral’s navigators had agreed that the fleet lay well to the east of the Scilly Isles. The naval sea disaster, in which over 2000 men died due to ignorance of longitude, prompted greater calls for more reliable means of navigation.

The English parliament established a “Board of Longitude” and offered a £20,000 reward (equivalent of about £2 million today) to anyone who could solve the problem of finding longitude at sea. The prize specified that the timekeeper had to perform reliably within two seconds per day and prove that it could maintain that rate on an ocean voyage of several years duration.

John Harrison, a carpenter from Lincolnshire, eventually won the prize. Harrison had invented an increasingly refined series of clocks. The first clock (known as “H.1”) is 3 feet square; the prize-winning version (known as “H.4”) is less than 6” in diameter and resembles a very large pocket watch. Both are on display today at the Royal Observatory in Greenwich. The prize was awarded in 1775 after Harrison’s H.4 timepiece successfully returned from a three-year exploratory ocean voyage with James Cook through the South Seas.

Harrison’s prize-winning improvements in timekeeping included not only producing a chronometer of reasonable size, but also methods of reducing friction, mitigating the effects of changing temperature, and making the timepiece less susceptible to sudden shocks and jars.

Over the next 15 years, Harrison’s marine timepiece evolved into the “marine chronometer. A version of H.4 remained the basis of the design, with further developments that both refined and simplified the chronometer, reducing its price and increasing its availability. By 1790, the fundamental design was established, remaining basically unaltered through the Second World War. The ports of London and Liverpool, well-established centers for maritime trades, became home to instrument workers who produced high quality chronometers.

  In order to remain accurate, chronometers are wound daily; a 2-day movement, however, gives a power reserve. In order to prevent deviation, chronometer movements are suspended on gimbals and inverted only for a minute during its daily rewinding.  

By 1850, all British naval ships were issued three marine chronometers to make sure the crew had the correct time, should one clock stop working properly. The demand for chronometers was temporarily revived by the need for navigational instruments during the World Wars. Hamilton Watch Company won the contract for supplying marine chronometers to the U.S. Navy; many of the improvements made to the chronometer by Hamilton eventually found their way into Hamilton pocket watches.

The post-war period saw the development of more modern methods of timekeeping.

One of the secrets of accuracy in timekeepers is to make the beat faster and the parts smaller. Early clocks had beats that lasted several seconds each. The marine chronometer had two beats per second. Quartz timepieces, first developed in the 1920s, vibrate a hundred thousand times a second. The first accurate atomic clock was built in 1955. In an atomic clock, as explained by the Why?Files Website of the University of Wisconsin, “oscillations occur in an electromagnetic field that causes transitions between two quantum-mechanical conditions of atoms. In the commonly used cesium 133 atoms, these occur at about 9.19 billion times per second.”

William J.H. Andrewes, editor. The quest for longitude. Cambridge, Mass.: The Harvard University Collection of Historical Scientific Instruments, 1996.
Duane A. Cline. Navigation in the age of discovery. Rogers, Ark.: Montfleury, Inc., 1990.
Dava Sobel. Longitude. New York: Walker & Co., 1995.
David S. Landes. Revolution in time: clocks & the making of the modern world. Cambridge, Mass.: Belknap Press, 1983.
Eric Bruton. The history of clocks and watches. New York: Rizzoli International Publications, 1979.

Online sources:
The Website of the National Watch & Clock Museum at
The Website of Proudman Oceanographic Laboratory, Liverpool, at
The Website of England’s National Maritime Museum and Royal Observatory at
The Website of the US Coast Guard Navigation Center at
The Why?Files Website of the University of Wisconsin at

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