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Red line down the middle is the Prime Meridian

The International Meridian Conference was a conference held in October 1884 in Washington, D.C. in the United States to determine the Prime Meridian of the world. It was held at the request of U.S. President Chester A. Arthur. Twenty-five nations were represented by 41 delegates.

The following resolutions were adopted by the conference:

1. That it is the opinion of this Congress that it is desirable to adopt a single prime meridian for all nations, in place of the multiplicity of initial meridians which now exist.
2. That the Conference proposes to the Governments here represented the adoption of the meridian passing through the centre of the transit instrument at the Observatory of Greenwich as the initial meridian for longitude.
3. That from this meridian longitude shall be counted in two directions up to 180 degrees, east longitude being plus and west longitude minus.
4. That the Conference proposes the adoption of a universal day for all purposes for which it may be found convenient, and which shall not interfere with the use of local or standard time where desirable.
5. That this universal day is to be a mean solar day; is to begin for all the world at the moment of mean midnight of the initial meridian, coinciding with the beginning of the civil day and date of that meridian; and is to be counted from zero up to twenty-four hours.
6. That the Conference expresses the hope that as soon as may be practicable the astronomical and nautical days will be arranged everywhere to begin at midnight.
7. That the Conference expresses the hope that the technical studies designed to regulate and extend the application of the decimal system to the division of angular space and of time shall be resumed, so as to permit the extension of this application to all cases in which it presents real advantages.

Resolution 2, fixing the meridian at Greenwich, was passed 22–1 (San Domingo, now the Dominican Republic, voted against); France and Brazil abstained. The French did not adopt the Greenwich meridian until 1911.

Resolution 4 expressly exempts standard time from the universal day. Although two delegates, including Sandford Fleming, proposed the adoption of standard time by all nations, other delegates objected, stating that it was outside the purview of the conference, so neither proposal was subjected to a vote. Thus the conference did not adopt any time zones, contrary to popular opinion.

Regarding resolution 6: Great Britain had already shifted the beginning of the nautical day from noon, twelve hours before midnight, to midnight in 1805, during the Battle of Trafalgar. The astronomical day was shifted from noon, twelve hours after midnight, to midnight effective 1 January 1925 by a resolution of the newly formed International Astronomical Union.

Wikimedia Commons has media related to:

International Meridian Conference

• Proceedings of the 1884 International Meridian Conference - notes with links to scanned page images at Steve Allen's site
• Proceedings of the 1884 International Meridian Conference - Text of the proceedings, from Project Gutenberg