NavList:

Lu, you wrote:
"So I'm not sure the IDL can be described as a "map maker's fiction" so much as an agreed-upon line where today turns into tomorrow heading west or today turns into yesterday heading east."

Oh, but it's not agreed upon. The 180 degree line, which mariners use to change the date, does have some standing in international maritime standards (details, anyone?). But that's not the so-called "International Date Line" which you will find snaking down the Pacific near 180. THAT has no basis in law or international agreement. It was invented by Joseph Schedler. It's a clever trick, but still a fiction.

You also wrote:
"I believe an intriguing piece of information would be what circumnavigators did before standardization of the prime meridian at Greenwich and, by implication, the IDL in the middle of the Pacific? How/where/when did the navigator on a circumnavigating ship skip the date forward or backward?"

I agree. That would be very helpful evidence. From the few examples I've encountered, they changed the date wherever and whenever convenient. Or not at all if they were going back the way they came. You probably saw my example of Nathaniel Bowditch in Manila in 1796. Manila was on the American date system, but they didn't bother to change their date aboard ship since they were going back by way of the Indian Ocean. I have a vague memory that on Cook's first circumnavigation they changed the date when they were back in the Atlantic a few weeks from home. Whaling ships in the nineteenth century would cross the whole Pacific without changing the date if they were going back the way they came. Some whalers did circumnavigations, whaling their way through the Indian Ocean into the Pacific and then back around Cape Horn, but it was much more common to go out and back via Cape Horn --no date change required. If they landed somewhere and found they were on the Asiatic date system, no problem, they understood the reason (but maybe darned inconvenient if one of them thought it was Sunday and the other thought it was a work day).

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?? :)

-FER

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