Marine chronometer

As longitudinal clock, marine chronometers, marine chronometers or watch the ship chronometers are called, have been used to determine the longitude. The introduction of this instrument, the determining longitude at sea with sufficient accuracy was possible for the first time.

Operation

The rotation of the earth leads to an apparent motion of the heavenly bodies (sun, stars, moon) in the sky. Since the Earth rotates by a known amount in a certain time, the time difference is of such events to the respective observation locations in a fixed ratio to the length difference of their positions.

The exact timing of such events (such as the meridian passage of the sun through the meridian ) is thus the location of the observer on the globe depend - and exclusively by its longitude, so his transfer to the East-West direction. With the help of a chronometer, the time difference of such an event is detected at the observation with the time at the place of this event are accurately known for both longitude and time. For this purpose, the chronometer must be synchronized with the time of the well-known town.

The difference in length can then be calculated from the observed time difference: As the complete rotation of the earth (360 ° ) for 24 hours or 1440 minutes takes a time difference results from exactly four minutes per degree difference in length. However, a deviation of the clock caused this error exactly the same amount - it is not possible to determine what proportion of the time difference to the current position reached and which is due to the previously reached deviation of the clock. Since sea voyages occasionally could take several weeks or months, a navigation watch was therefore only possible to be sufficiently accurate continuous by this method could be produced.

History

The problem of determining longitude at sea employed for centuries all the nations with ocean-going ships. So prize money to solve the length problem was exposed in England in 1714, but failed all previous concepts to their lack of practicality.

A tenacious fighter for the concept of longitudinal clock on sea voyages and builder of the first watch with sufficient accuracy was John Harrison. Already in 1735 he created the first clock before, but could only prevail in 1759 with his fourth model on a broader basis with its concept.

The comprehensive equipment of ships with length of watches began in England in the late years of the 18th century and was not fully completed until about 1840. From 1829 was installed in many ports time balls to facilitate Uhrenüberpüfung, most have been torn down in the 1920s, since 1907, there was time signal transmitter.

Today, the position determination on ships mainly takes place by means of satellite navigation. Mechanical ship's clocks are usually no longer in use, but today fulfill a purely decorative purposes.