DATELINE


Magellan's globe-girdling voyage went west in 1519. His ships crossed the Atlantic, Pacific, and Indian Oceans, came around Cape Horn, and finally landed in West Africa, where Portuguese locals told the surviving captain that it was Wednesday. That didn't make sense. He'd kept careful track of the time. He knew it was Thursday.
That was the first time anyone had faced the date line problem. It was a drama that would play many times through the 16th century. As settlers moved east and west, they met -- usually in the Pacific -- and there they disagreed on the date.
The date change soon mutated from mystery and surprise into annoyance. By the 19th century, settlers who'd gone west carried their time as far the Philippines. But Guam and New Zealand are far this side of the Philippines. They were settled by Dutch who'd sailed east. So it was Tuesday in the central Pacific while it was still Monday out in the Philippines.
So the Pacific people had to struggle with American time and Asiatic time. All Europe wanted was to keep the date change out of sight. If the Greenwich meridian went through London (the center of their universe), the most remote place on Earth was the 180th meridian. That was clearly the place to reset calendars.


The effect of ignoring the date line is also seen in Jules Verne's novel Around the World in Eighty Days, in which the travellers, led by Phileas Fogg, return to London after a trip around the world, thinking that they have lost the bet that is the central premise of the story. Having circumnavigated in the direction opposite Magellan's, they believe the date there to be one day later than it truly is.
Lest anyone accuse Fogg of cheating by obtaining one extra day, this is not so. Assuming a constant eastward speed, each day was 18 minutes short of a full 24 hours, accumulating one full day, which they regain by setting their calendars back a day in mid-Pacific.
Anyone travelling west and passing the line must add a day to what they would otherwise expect the date and time to be. Correspondingly, those going east must subtract a day. Magellan's crew and Verne's travellers neglected to make those respective adjustments.


In 1841, the American mystery writer Edgar Allen Poe (1809 - 1849) made use of the properties of the date line in his short story “Three Sundays in a Week” (first published as “A Succession of Sundays” in the Saturday Evening Post, 27 November 1841) in which a wealthy man promises the hand of his niece (and her plum) with a sizeable dowry to a young man, on the seemingly impossible condition that a marriage could only be possible if it occurred “when three Sundays come together in a week”. The condition was satisfied several weeks later when the parties concerned were visited on a Sunday by two navy captains who had each just completed a circumnavigation of the world. The first, who had travelled in a eastward direction, argued that it was Monday and that the previous day had been a Sunday. The second, having travelled in a westward direction, countered that it was a Saturday and that Sunday was not until the next day.

What appears to be the earliest reference to the circumnavigator’s paradox is found in the works of the Syrian prince and geographer-historian Isma‘il ibn ‘Ali ibn Mahmud ibn Muhammad ibn Taqi ad-Din ‘Umar ibn Shahanshah ibn Ayyub al Malik al Mu’ayyad ‘Imad ad-Din Abu ’l-Fida (1273 - 1331). In his Taqwin al-Buldan, Abu ’l-Fida described how a traveller, depending on his direction of travel, would either lose or gain a day at the completion of his circumnavigation.


Another early reference to the circumnavigator’s paradox is found in the works of the French scholar Nicole Oresme (c. 1325 - 1382). In his Traitié de l’espere (which was also translated into Latin as the Tractatus sperae), Oresme presented a “remarkable circling of the Earth” by two imaginary travellers Jehan and Pierre (Johannes and Petrus in the Latin version) who set out to journey around the world along the equator in opposite directions at a speed of 30 degrees of longitude per 24-hour day. Jehan, travelling in a westward direction, would claim at the completion of his journey that it took him only eleven days and nights while Pierre, travelling in an eastward direction, maintained that it lasted thirteen days and nights. A third man, Robert, who had remained at the starting point, would however point out that only twelve days and nights had elapsed since both travellers had set out.


Oresme repeated this argument in his Quaestiones supra speram, a series of clarifications of questions based on the popular cosmographical treatise De sphaera by Sacrobosco, in which he renamed his travellers Plato and Socrates and the ‘control’ Petrus and allowed both travellers a more leisurely pace of 14.4 degrees of longitude per 24-hour day. At the return of the philosophers at the starting point, Plato (the westward traveller) would have logged twenty-four days, Socrates (the eastward traveller) no less than twenty-six days, while Petrus saw the sun rise and set only twenty-five times.
Around 1377 Oresme wrote his Traitié du ciel et du monde, a French translation and commentary of Aristotle’s De caelo et mundo, in which he again discussed the circumnavigator’s paradox. Here the westward traveller is simply named A, the eastward traveller B and the control C. Each of both travellers is now assumed to cover 40 degrees of longitude per 24-hour day; A counting eight days for his circumnavigation, B ten days, while C only marks nine days on his calendar.


In order to resolve the circumnavigator’s paradox for future travellers, Oresme concluded his discussion of the imaginary journeys of Plato and Socrates in the Quaestiones supra speram with the observation:
“From this it follows that if this [equatorial] zone were everywhere habitable, one ought to assign a definite place where a change of the name of the day would be made, for otherwise Socrates would have two names for the same day and the other [Plato] would have the same name for two days.”

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