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The Longitude Act
In 1714 Parliament passed the Longitude Act, which created the Board of Longitude. A reward was set at 20,000 pounds (the equivalent of millions of dollars today) for anyone who could find an accurate way to find longitude at sea. The board of Longitude required a form of determining longitude that was accurate to half a degree (sixty nautical miles) after a six week voyage to the West Indies. -
Construction of H1 begins
John Harrison begins his construction of the first chronometer. -
H1 completed
The H1 chronometer used a balance spring with two 5 pound weights connected by brass arcs. When the clock was tilted or turned by the movement of the sea, the weights attached will balance the spring and any particular movement communicated to one balance will be automatically counteracted by an equal and opposite movement of its opposing counterpart. The chronometer weighed 72 pounds. The first time H1 was tested it lost 3 seconds in 24 hours, a success, but not good enough for long sea voyage -
H2 completed
H2 was taller and heavier than the H1 but it took up less deck space. The most important improvement from the H1 to the H2 was a remontoire. The remontoire mechanism ensures that the force on the escapement is constant, thus improving the accuracy of the clock. -
H3 completed
The Design of the H3 was very similar to the H2 but it was slightly shorter, lighter and had circular balances instead of dumb-bell shapes. The H3 incorporated both an advanced anti-friction bearing and a bi-metallic strip to compensate for temperature variations, both brilliant innovations. -
H4 completed
The H4 was by far the smallest of the chronometers, with a diameter of only 5.25 inches. To minimize the problems of ageing oil, Harrison used wheels and pinions with a great number of teeth to increased the efficiency of the clock. The H4 was tested on a sea voyage to Jamaica, it lost only 5.1 seconds 2 months. -
H5 completed
The H5 was the most accurate and technologically advanced of the chronometers. Its design was very similar to that of H4.
