Cornish Astronomer Secures The Prime Meridian of The World for Britain In 1884

An article on by Brian Sheen

A hundred and twenty years ago a triumphant John Couch Adams returned to Britain after difficult month in America. It had been clear for some while that the worlds shipping was in difficulty as the charts in use were based on a variety of Prime Meridians. The Americans called a Conference in Washington to resolve the situation. Britain's principal delegate was Couch Adams as Director of the Cambridge Observatory.

The main contenders were Britain, France, Germany and Russia. America did not want to get involved in view of the number of time zones that cross that country. Couch Adams is of course remembered as the young astronomer who in 1845 predicted the position of the new planet Neptune. However much of his life was devoted to obtaining accurate positional data. In addition he studied terrestrial magnetism and its variation across the globe.

The main factors that favoured Greenwich as the site of the Prime Meridian were:-

  • The fact that Britain had far more shipping and far more ships using the Greenwich Meridian than the rest of the world put together. These charts were started in 1767 by the British Nautical Almanac.
  • That the Greenwich Observatory had been producing data of the highest quality for a very long time.

The French, it might be argued, realising they were unlikely to get Paris accepted by direct logic tried to discredit the British claim by suggesting the Fortunate Isles. This location was used by Marius, Ptolemy and Richelieu.

Adams countered by saying that the Meridian relied on astronomical data and therefore an accurate telescope (Transit Circle) something that no astronomically remote place possessed. An attempt was made to get around the nationalistic aspect of Greenwich, by Stanford Fleming, the representative of Canada. He suggested that a half Meridian be adopted opposite Greenwich where the International Date Line now runs. Adams stated that the Date Line or half Meridian still had its origins in the Transit Instrument at Greenwich Observatory and therefore did not dispose of the nationality aspect.

The Greenwich Observatory had been established in 1675 to provide accurate charts for the Navy. These charts all depend on timing stars as they pass a Transit Telescope, these special telescopes require very precise setting up and maintenance. For many years this responsible task had been undertaken by Truro born Edwin Dunkin as Chief Assistant to the Astronomer Royal. George Bidell Airy had built the "new" Transit Telescope at Greenwich in 1850, he retired in 1881. Dunkin, was one of very few who entered the Observatory as a "Computer", a junior clerk and then rose through the ranks to become Chief Assistant to the Astronomer Royal in effect his deputy. For many years Airy had entrusted Dunkin with commissioning all the new instruments brought into the Observatory. In 1854 he determined the longitude of the Paris Observatory and thereby the difference between the longitude of Greenwich and Paris, very useful information following the Conference.

The Conference adopted Greenwich as the Prime Meridian with the French rather upset. So due, at least in part, to Adams' logical approach the terms Greenwich Mean Time, AM ante meridian and PM, post meridian came into being.

The French stuck to Paris time, in 1896 Greenwich time was accepted as "Paris time less nine minutes". It was not repealed until August 1978 when the French adopted Co-ordinated Universal Time, basically Greenwich time under a scientific name. The Army in the form of the Ordnance Survey refused to accept the Airy Meridian and continue to use the old Meridian based on Pond/Bradley's' original instrument some 19' to the west for the maps of the UK.

Now Britain and France seem to share the last word. In 1963 the UK/US system was made fully international and operated under the control of Bureau International de l'Heure in Paris. It is called Co-ordinated Universal Time, which as noted above is very close to Greenwich Time.

Further Reading.

E.Dunkin "A far off vision - a Cornishman at Greenwich Observatory, Pub. Royal Institution of Cornwall 1999.

D.Sobel "Longitude"Pub Fourth Estate, 1996.

Various "The Old Royal Observatory Greenwich, Guide to the Collections. Pub. Merrell Holberton, 1998

H.M. Harrison "Voyager in time and space", Pub Book Guild, 1994.


Gilbert Satterthwaite authority on the Airy Instruments for help and advice.

Images by kind permission of Ethel Roseveare via Rosemare Pritchard.


Home - News - Contact Us - Links - Articles - About Us