Chronometre Joseph Sewill Liverpool 1862

Marine chronometer by Joseph Sewill 1862 with its mahogany box
Manufacturer for the Admiralty of Great Britain

Exhibit outstanding mechanical model to rocket and helical chain. L works
Marine chronometer
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Antiques Marine

Is called marine chronometer, a watch especially for large format to keep the time on the boat. The marine chronometer has various features:
1) It is almost always provided with a detent escapement and second hand needle jumped every half-second.
2) It is equipped with a rocket, special device, responsible for regulating the force of the mainspring.
3) The marine chronometer is mounted on a suspension called «gimbal» as the compass edge, arranged so that said timer occupies a horizontal position regardless of movement or position of the boat.
Is an instrument of very high precision that is used in particular to the so-called astro navigation with a sextant.
Some timers are set to sidereal time. The principle of determining longitude is very short, as follows:
The ship leaves port, the timer is set to the time of the meridian of Greenwich, it has also special tables (Knowledge of Time, Nautical Almanac, etc. ). These tables indicate, for each day of the year, time of passage of the sun and certain stars over the meridian of Greenwich.
To determine longitude, the officer in charge to take stock, keep using his stopwatch time of passage of any star, or sun, in its own meridian. The difference between the time of the passage and the time that the star must pass the meridian of Greenwich, said, hours, minutes and seconds, the difference of longitude between Greenwich and place of observation.
Also employed, navigation, watches smaller format, known as the clocks on board (in English DeckWatch).
Is a key piece in a collection of marine antiques.