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On 2011-07-10 07:07, Frank Reed wrote:

Oh and to reiterate something that I wrote in a post to John, the fact that the date line, however defined, is near 180 degrees longitude is not necessarily connected with the choice of Greenwich as the Prime Meridian. If Washington, DC had been chosen as the Prime Meridian, would you really run the date line through 180 degrees from Washington?? :)

I think there is such a connection, and you are yourself making a strong argument for it, but the reasoning went the opposite way.

If the proposal of the IGA conference in Rome (1883) would have been adopted (i.e. chosing Greenwich and counting the day from noon), the date line would run across Europe. This is probably the reason why nothing came of it. Be it that the astronomers meeting in Washington were more practically involved in time reckoning than the geodesists meeting a year earlier, or simply that the delegates in Washington had specific political mandates from their governments; the fact is that the problem of date brake became a concern at the conference in Washington. E.g. Struve proposed to place the prime meridian at the anti-meridian of Greenwich, to have it out of the way of civilization, where the discontinuity in date (and longitude, if counted from 0 to 360!) would inconvenience only a few Tschouktschis. Others recognized that the same goal could be achieved more elegantly by counting the "cosmopolitan" day from midnight instead of noon (and longitude in both directions).

It was the combination of there having been a respectable transit instrument centered on the chosen meridian and no sign of civilization anywhere on its anti-meridian that won the day for Greenwich.

Herbert Prinz