Today, we try to make sense of the International Date Line. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

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.

But the central Pacific isn't empty. A hundred vested interests sent the line zigging here and zagging there. The king of Samoa, under pressure to adopt "American" time, said: "Look, if we use Asiatic time, then America will observe the Fourth of July two days in a row."

Finally, an 1884 conference created an International Date Line. Alaska had been on Asian time when it belonged to Russia. The International Date Line still doglegs far east to pass through the Bering Straits. That keeps all of Russia on Asian time. Then the line lurches west to keep the Aleutians on American time. When it's Tuesday in Japan and at the tip of Siberia, it's still Monday in western Alaska. The problem is, much of Siberia lies far this side of Western Alaska.

The line doglegs east a second time to keep Tonga, Fiji, and New Zealand on Asian time. Today, Tonga and Samoa -- next-door neighbors -- have to run on different time. Protestants who keep a strict Sabbath settled both island groups. Both now restrict travel on Sunday, but Sunday occurs twice in a row. The result? Regional travel grinds to a halt two days out of seven.

The date line seems simple enough. Yet it leads us into subtle confusions. The problems it poses keep coming back -- both to tease us and to surprise us.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Winchester, S., Where Time Begins. Condé Nast Traveler, January 1990, pp. 100-102 and 145-146.