AN EXTRA DAY IN THE CALENDAR.
“There is an island off the coast of New Zealand where the day of the week changes. There Saturday is Sunday, and Sunday, Monday. When Sunday noon closes, Monday noon begins. A man sits down to his dinner Sunday noon, and it is Monday noon before he is done eating.”
A correspondent sends us the above statement and asks, is it correct? We answer: Not to the islanders, who, as ourselves, have but 365 solar days in a year. But to a stranger coming there on his voyage round the world, who has 366 at his disposal, it is true. He has one day to spare, has no name or place for it in the week, and just drops it out of his reckoning, as though it had never been. The explanation is simple enough, even for the young. The revolution of the earth on its axis, from west to east, once in 24 hours, gives the sun an apparent motion round the earth from east to west. To us the sun rises and sets. The succession of day and night is just the same as if the sun really went round the earth. As the sun’s apparent motion is from east to west, a man traveling eastward, at whatever speed, will see the sun rise, reach the meridian, and set, a little sooner each day than the day before. So the time indicated by his watch, and that by the sun will differ more and more as he goes on; and what he gains each day in time will evidently be to a solar day, as the distance traveled is to the earth’s circumference. One degree east will make a difference of four minutes, fifteen degrees an hour, one hundred and eighty degrees twelve hours. Having reached the one hundred and eightieth meridian, his chronometer and the sun are just twelve hours apart, so he changes his reckoning, to avoid confusion, and at noon Sunday calls it Monday. The correction is of course too much, but if he waits till beyond that time it amounts to more than half a day, and is constantly increasing. If the error is to be corrected all at once—and this is the only way that is found practicable—it should be done when it amounts to half a day. When he has completed the circuit of the earth a whole day will have been gained. If another man, from the same place of departure, go west, or with the sun, he will lose a day, and the two meeting would be, if neither had changed his reckoning, two whole days apart—yet each had the same number of hours and minutes. He who had the greater number of days had them just so much shorter. There is, of course, no reason in the nature of things, why the days of the week should be changed on the one hundred and eightieth meridian rather than elsewhere. There must be some point from which longitude is reckoned, and to avoid confusion English and American navigators agree on Greenwich, near London, and their nautical charts, almanacs, etc., are arranged accordingly. If they had taken as their starting point Washington, the one hundred and eightieth meridian would have been west of where it is, the number of degrees between the places.
