Moon Rise, Moon Set and the Tide Clock

What is a tide clock? For the millions of Americans who live miles from the ocean, what exactly are the tides and why are they important? Tide is defined in the dictionary as the alternate rising and falling of the seas, about every twelve hours, in response to the gravitational attractions of the moon and the sun. There can be a dramatic increase in wave action, the size of waves and the depth of water in shallow areas between high tide and low tide. High tide represents the time period when the water is at its highest level for the approximate twelve hour period while low tide is the opposite.

Importance of Tides

Obviously the level of the water is important to anyone who plans on boating, from ocean cruise ships to commercial fishing to recreational boating. Even ordinary people who want to take their kids to an ocean beach appreciate knowing when high and low tides will be occurring. Families with small children may prefer to visit the beach at low tide when the waves will be shallower and weaker while teenagers who want to try their hand at surfing may seek the larger waves of high tide.

On a more important scale, for example, if a hurricane makes landfall at or near high tide, its effects will generally be more severe because the deeper water and higher waves of high tide will be pushed inland causing more shore damage and flooding than at low tide. Also, for example, some coastal areas are devoid of water at low tide and some navigation channels can accept boat traffic only at high tide. The bottom line is that the tides are important to anyone involved with the ocean.

Tides and Time

The time of day when high or low tides occur varies similar to sunrise and sunset except that tides are also dependent upon the position of the earth relative to the position of the moon. Complex calculations are involved with predicting when the tides occur. The National Ocean Service, a division of the National Oceanic and Atmospheric Administration (NOAA), is responsible for publishing tide tables that predict high and low tides for every tidal reference station in the United States. Ordinary citizens can access these tables through the local newspaper of cities near the ocean or online.

These tidal reference tables can be hard to read and are useless to someone who is spending the week on vacation at a beach house without a newspaper or computer hook-up or on their boat. Enter the handy invention of the tide clock. This clock does not tell time but indicates the current position in the approximate twelve-hour tide cycle. Only one hand or indicator is needed and the dial is divided into two equivalent six-hour segments. In addition to two sets of numbers from 1 to 6, the dial of the clock is labeled as high tide and low tide.

The clock does not indicate the time of day in any way, unless it is a combination model that does tell time of day. The stand-alone tide clock indicates a relative time until the next occurrence of a high or low tide. For example, if the hand is pointing to a 3 in the half of the clock that is indicates low tide, there are approximately three hours left until low tide occurs. Since the tides are completely different for the Atlantic and Pacific coasts of the Unites States, tide clocks must be calibrated for one ocean or the other.

History of Tide Clocks

The history of these clocks can be traced back to England in the 1600’s. Henry Philippes of London published a tide table for the Thames River in 1668 while Royal Astronomer John Flamsteed, also of London, is well known for his work on tide tables from 1683 to 1693. Since Flamsteed was a contemporary of Isaac Newton, Isaac Newton also became interested in tides and determined that the tide was dependent upon the moon. Meanwhile, Thomas Thompion, a respected clockmaker in London, created the first tide clock, a longcase clock, in the mid-1670’s. Two such clocks were made and they both indicated the time of high tide at London Bridge.

James Furguson, a Scottish astronomer and instrument maker who lived from 1710 to 1776, not only studied tides but designed a tide clock which combined a clock that indicated time with a manual tide dial. The clock owner would manually set the tide dial to high tide once.

Other clockmakers soon incorporated a tide dial in English clocks of the period and these tide clocks became popular in seafaring regions of England throughout the eighteenth century. If the tide clock was created for just one location the tide dial often was incorporated with the phase of the moon dial and was not adjustable. These clocks used just one hand to show both the phase of the moon and the time of high tide.

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