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John Harrison

During the Great Age of Discovery, when Christopher Columbus discovered the Americas, there was no method for accurately measuring the position of one’s ship on the ocean, and there were many accidents in which ships sank. The British clockmaker John Harrison developed an accurate clock to make safe ocean voyages a reality. Harrison’s invention made it possible for people to navigate the oceans of the world safely.
Why were accurate clocks needed for safe ocean navigation? At the time, people could tell the latitude (north-south position) of their ship by finding the position of the sun and Polaris, but there was no accurate method for measuring latitude (east-west position). Because of this, there were many ships that became lost at sea.
Longitude Shows how far west (or east) the position of the ship is from the port of departure. Latitude Shows how far south (or north) the position of the ship is from the equator.
Scientists focused their attention on the fact that the earth is round, and thought like this. A circle has 360 degrees, and the earth rotates one full circle every 24 hours. That means that it rotates 15 degrees every hour.　360 degrees（latitude） ÷ 24 hours（one rotation of the earth） ＝ 15 degrees (a one-hourtime difference means a difference of 15 degrees of latitude)
For example, if we have an accurate clock, we can set the time shown by the clock to 12 noon when the sun is at its highest position in the sky while we are at port, and leave port with the clock onboard. Then, after travelling for several days on a long voyage, and when the sun is at its highest and we know that it is 12 noon, if the ship’s clock (i.e. the time at our port of departure) shows 4PM then we know have a time difference of four hours. That means that we are now 60 degrees west of our port of departure.　That way we won’t get lost when we‘re out at sea!
I can’t believe that he managed to make his sea clocks so much smaller, lighter and more accurate over just 26 years.
Harrison learned to build clocks by repairing clocks made by other people, and teaching himself about physics and mechanics, while working as a carpenter. He kept trying for decades to build an accurate marine clock, and eventually succeeded in creating a small and very accurate marine chronometer.
As long as we have one of those, we won’t get lost at sea any more, huh?!
John Harrison
During the Great Age of Discovery, when Christopher Columbus discovered the Americas, there was no method for accurately measuring the position of one’s ship on the ocean, and there were many accidents in which ships sank. The British clockmaker John Harrison developed an accurate clock to make safe ocean voyages a reality. Harrison’s invention made it possible for people to navigate the oceans of the world safely.
Why were accurate clocks needed for safe ocean navigation?
At the time, people could tell the latitude (north-south position) of their ship by finding the position of the sun and Polaris, but there was no accurate method for measuring latitude (east-west position). Because of this, there were many ships that became lost at sea.
Scientists focused their attention on the fact that the earth is round, and thought like this. A circle has 360 degrees, and the earth rotates one full circle every 24 hours. That means that it rotates 15 degrees every hour.　360 degrees（latitude） ÷ 24 hours（one rotation of the earth） ＝ 15 degrees (a one-hourtime difference means a difference of 15 degrees of latitude)
For example, if we have an accurate clock, we can set the time shown by the clock to 12 noon when the sun is at its highest position in the sky while we are at port, and leave port with the clock onboard. Then, after travelling for several days on a long voyage, and when the sun is at its highest and we know that it is 12 noon, if the ship’s clock (i.e. the time at our port of departure) shows 4PM then we know have a time difference of four hours. That means that we are now 60 degrees west of our port of departure.
In 1735 H-1 *Harrison’s first navigational sea clock. (Marine Chronometer)　Height: 63cm;　Width: 70cm　Depth: 45cm;　Weight: 34kg　In 1761 H-4　Diameter: 13cm;　Weight 1.4kg
I can’t believe that he managed to make his sea clocks so much smaller, lighter and more accurate over just 26 years.
Harrison learned to build clocks by repairing clocks made by other people, and teaching himself about physics and mechanics, while working as a carpenter. He kept trying for decades to build an accurate marine clock, and eventually succeeded in creating a small and very accurate marine chronometer.
As long as we have one of those, we won’t get lost at sea any more, huh?!
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Famous People in Time

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  • Galileo Galilei
  • Christiaan Huygens
  • John Harrison