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Harrison's four chronometers

Harrison's four chronometers

John Harrison spent more than 40 years perfecting the chronometer. He refined his designs by painstakingly building four different timepieces. Each chronometer, more compact and accurate than the last, took many years to make. His instruments were subjected to rigorous testing by Britain's Board of Longitude. Harrison's final design remains the basis for chronometer design more than 200 years later.

A time-keeping device used in the eighteenth century. It has a central gold-coloured and textured oval plaque with four clocks arranged in it. Under the plaque is a base made up of three long brass plaques arranged one in front of the other. Above the base and behind the clock plaque is what appears to be a brass housing for the chronometer's mechanism. Three structures protrude vertically from the housing; a central flat strip section and two motion or governor devices that appear to be related to the mechanism. A series of arms protrude out and down at an angle from the underside of the central housing. The entire unit is mounted on a low purple cloth-covered display base. Behind is a studio backdrop of the same colour.

 

 

John Harrison's first marine chronometer, H1, was created in 1736.
Courtesy: National Maritime Museum, London.

A timekeeping device from the eighteenth century. It is a tall brass box. The side facing the camera has a large 'u' shaped opening in the upper middle and several holes in its lower part. A series of small thin wheels and springs are mounted around the bottom right hand corner of the face. The internal mechanism of the device can be seen through the front face opening. Several large arms criss-cross the inside space; other parts of the mechanism are visible. A callibrated plaque is mounted above the interior. Another plaque is mounted at the top of the front face. It has ornate decoration and what may be the maker's details on it. Another plaque is mounted lower down. It has a clock face and a rotating read-out installed on it.

 

 

John Harrison's second marine chronometer, H2, was created in 1737. Courtesy: National Maritime Museum, London.

A timekeeping device from the eighteenth century. It is a tall brass box with open sides. The front face has a plaque mounted on it with some calibrations and other markings. Behind the front face is the mechanism. The edges of several wheels and cogs protrude out on both sides behind the face. One large wheel protrudes above the mechanism. It passes through two armatures that are connected to the main mechanism. The entire device sits on a purple-coloured studio backdrop cloth. The background is in shadow.

 

 

John Harrison's third marine chronometer, H3, was created in 1761.
Courtesy: National Maritime Museum, London.

A timekeeping device from the eighteenth century. It has a traditional clock appearance. The outer section is finished in silver. At the top is a large winding crown with a horse-shoe-style handle attached to it. At the left of the outer section is a raised piece with a flat edge. The white clock face has ornate patterns in black at the twelve, three, six and nine postions. Inside these decorations is a circle with the number sixty at the twelve position and then counting clockwise in five second intervals, all in black numbers. The usual hour markings are inside that circle, in black type. They are in Roman numerals. The hour hand is at the two position and the minute hand is at the ten position.

 

 

John Harrison's fourth marine chronometer, H4, was created in 1761. Courtesy: National Maritime Museum, London.