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
- 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
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
Gilbert Satterthwaite authority on the Airy Instruments for
help and advice.
Images by kind permission of Ethel Roseveare via Rosemare