India, April 14 -- In the 1850s, some three decades before the international Date Line was established, the author and mathematician Lewis Carroll puzzled over a question of time. I quote: "Suppose yourself to start from London at mid-day on Tuesday, and to travel with the sun, thus reaching London again at mid-day on Wednesday. If at the end of every hour you ask the English residents in the place you have reached the name of the day, you must at last reach some place where the answer changes to Wednesday."

Given that it's always midday (or noon) at every place the traveller is reaching, Carroll wondered about the point where the day changed from Tuesday to Wednesday. Back in the 1980s, when I described Carroll's question, a friend of m...