A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John Huth
Date: 2011 Jul 8, 09:15 -0400
John H., you wrote:
"By that logic you'd lump the Greenwich Prime Meridian and time zones in the same category."
No. The Greenwich Prime Meridian was the result of long negotiations and an international conference. Standard time zones were the product of commercial necessity and economic efficiency (they were, of course, known previously as "railroad time" in the US) and they were enacted by national laws. But the "international date line" is a very different thing. Drawing this line on a globe was apparently the specific invention of one man or perhaps a small group of people. It appears, from what I have found, that it was specifically invented by Joseph Schedler of New York around 1876 and published in his "Manual for the Use of Globes". You can read this online at archive.org (the 1878 publication). But there was no conference and no set of laws that established it. And I do believe that Schedler himself coined the term, marking himself as a genuine wordsmith. Of course, the idea that you have to change the date when you circumnavigate has been known for centuries, literally since Magellan. It's the concept of this specific line with a bend here and an edge there that is a "mapmakers' fiction". Generations of explorers, traders, whalers, etc. crossed the Pacific well aware of the concept but without any need for a line on the chart labeled "International Date Line".
A better term might for the "international date line" might be a "mapmakers' clever trick" instead of a "fiction". It embodies an algorithm for deciding whether you need to change the date when you arrive at your destination. Rather than signalling that you have to change the date right when you cross the line or nearly so, which is what most people believe, instead it can be used as a tool for deciding whether a change will be required upon arrival. Draw your path across the Pacific from your departure point to your destination. If you cross the date line, no matter how it is drawn in detail (assuming no gross errors), one time or any odd number of times, then you have to change the date by one day. If you cross an even number of times, there is no change. Of course this is just one algorithm. You could drop the I.D.L. altogether (not much fun for globe makers and cartographers and their competitive business) and just use a slightly different font for the name of each island or country depending on whether it uses the eastern hemisphere or the western hemisphere date. Then you just look up your destination. If it's different from your departure in that special font characteristic, you make the day change upon arrival.
It is interesting to note that the expression "international date line" does not even appear in the "American Practical Navigator" (originally by Bowditch) until 1958. That strikes me as an interesting measure of its lack of importance! The maritime equivalent, where the date is changed at 180 degrees longitude regardless of the practice on nearby islands, does not appear in the Navigator until sometime after 1926 and before 1938. Previous to this era, it's not even worth mentioning. Remarkably, Nathaniel Bowditch himself encountered the issue way back in 1796 when he was visiting Manila as supercargo of the Salem ship Astraea. In his journal he noted that his crew had to work on a Sunday according to their reckoning (something they were not inclined to do since they were good Christians all, but you gotta what you gotta do) because in the port of Manila it was Saturday. In other words, they kept the date on board distinct from the date in port and reasonably so since they were returning via the Indian Ocean. After noting this, Bowditch wrote, "The cause of this difference was that the first discoverers and settlers of these islands came here by way of Cape Horn and we came by way of the Cape of Good Hope. Consequently there ought to be one day difference. But it is rather curious that in all other places of India and China they count their time in the same manner as we do on shipboard. It has often been proposed to alter this manner of computation but the clergy has not been fond of innovation and are averse to it and it cannot be done but with the consent of the Patriarch at Madrid." In fact, it was not until 1844/45 that the Philippines were officially shifted to the Eastern hemisphere date by dropping one day from the calendar (since the long-lived historical link to Mexico via the annual "Manila galleon" had been broken by loss of the Spanish colonies in the Americas). It's interesting to note that Schedler's initial map of the "international date line" got this wrong. He still placed the Philippines on the American side of his "date line" (that is, his date line took a big detour to the west), and even during the Spanish-American War there was some lingering confusion in the US whether a date reported from Admiral Dewey's fleet was a Sunday or a Monday.
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