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Longitude 2 - The prize

"Longitude Act 1714" by LiveRail - Photographed in National Maritime Museum, LondonPreviously published: Not previosly published. Licensed under CC BY-SA 3.0 via Wikimedia Commons -

Download a transcript of the introduction here


The Government set up a Board of Longitude to oversee the award of a prize of up to £20,000. That is about £1.5 million pounds in today's money.

The problem was well known. In order to find longitude you must know the difference between your local time and Greenwich time. A solution that really worked and could be tested at sea was the aim and nobody had yet come up with one.

Solving the problem- clocks and stars


1. Clocks and pocket watches were made before 1714. Why would they not have been suitable for telling the time at sea?

2. Astronomical observations can be used to measure time, for example the timing of the orbits of the moons of Jupiter. Why would making those observations be difficult at sea?

3. Is this a scientific or a technical problem?



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Credit: Cambridge University Library

‘Whereas it is well known by all that are acquainted with the Art of Navigation, That nothing is so much wanted and desired at Sea, as the Discovery of the Longitude, for the Safety and Quickness of Voyages, the Preservation of Ships and the Lives of Men : And whereas in the Judgment of Able Mathematicians and Navigators, several Methods have already been Discovered, true in Theory, though very Difficult in Practice, some of which (there is reason to expect) may be capable of Improvement, some already Discovered may be proposed to the Publick, and others may be Invented hereafter : And whereas such a Discovery would be of particular Advantage to the Trade of Great Britain, and very much for the Honour of this Kingdom;…’

Credit: Celestronimages

One idea was to use the positions of Jupiter's moons as an astronomical clock. Their positions had been observed and recorded for many years. In 1714 telescopes were not very good and at sea it was impossible to hold them steady. In cloudy weather they could not be seen anyway.
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