INTERNATIONAL DATE LINE. The imaginary line at which 'dates change, being made later by one day by those who cross the line from east to west and earlier by one day by those crossing it from west to east. It is a somewhat irregular line drawn through the Pacific Ocean in a general northerly and south erly direction and separating the islands of the Pacific Ocean in such a manner that all those lying to the east of it carry the same date as the United States, while all those on the west of it carry the same date as Japan and Aus tralia. If a person start at midday, that is, when the sun was shining perpendicularly on the meridian that passes through the place of starting, and travel westward, keeping pace with the sun, thus keeping the sun directly over the meridian of the place at which he might be, he would make a complete journey around the globe in twenty-four hours and return to his place of starting at noon the next day. Twenty four hours would have passed, but to the trav eler the sun would have been shining perpen dicularly as at noon all the time; and the ques tion arises, when or at what point did the trav eler change from noon of one day to noon of the next? For instance, if he should start at Monday noon and keep the sun in the zenith, he would arrive at the place of starting Tues day noon — it would be noon-day to him dur ing the whole journey of 24 hours. Monday noon would change to Tuesday noon without an intervening night; where would the change occur? It is to him apparently still Monday noon and to obtain the correct date he must drop a day. The reason for dropping a day can be more fully shown as follows: Remem bering that the earth makes one complete revolution on its axis in 24 hours and thus the sun in its apparent diurnal revolution moves over 360 degrees of space in 24 hours, it thus moves over 15 degrees of space in one hour, from which it is evident that the difference in longitude which causes the difference in the relative time, may be estimated in time, allow ing 15 degrees to an hour, or one degree to four minutes. Therefore, suppose a man start ing from any given point travel one degree west, his watch, instead of marking 12 o'clock at noon, according to the correct time at that place, would mark four minutes after 12. Let him travel west 15 degrees, and he will find that one o'clock by his watch will be noonday by the sun. Let him go on to 120 degrees and when the sun is in the zenith his watch will indicate eight o'clock P.M. Completing his
journey around the globe, he will have gained, in this manner, 24 hours. From this it will be seen that in order to obtain the correct date 24 hours must be subtracted from his time. On the other hand if a person could travel east ward at the same speed with which the sun apparently travels westward (the same rate of speed with which the earth revolves on its axis), if he should start on his journey at noon day, he would meet the sun when exactly on the opposite side of the earth from the place of starting and continuing the journey would again meet the sun at the place of starting, thus seeing three noondays within the 24 hours, or apparently gaining a day. This we know to be impossible, since only 24 hours of time have passed, while in reality an extra period of light has been gained and thus to obtain the correct local date a day must be added to your tune. From this we see that, for every time a person travels around the earth in either direc tion there is a difference in time of one day and the result is the same regardless of the rate of speed. To avoid the confusion of dates which must necessarily result from this con stant gain on one side and loss on the other, it has been proposed to determine upon some line at which eastern bound travelers shall add one day and westward bound travelers shall drop a day from their reckoning and thus prevent a disagreement in regard to the day of the week. The line at which this addition or subtraction shall be made is what is meant by the date line.
The dates in use upon most of the Pacific Islands and groups of islands are those which result from those carried by the first European or American colonists, these dates differing according as the colonists came from the east or the west. But, this is not time universally, because arbitrary changes are known to have been made in a number of cases, such as Alaska, the Philippines, etc. When Alaska was first colonized by the Russians it had the Russian date. When American settlers moved there, they carried with them the date of the United States which led to considerable con fusion, the Sunday of the Americans being the Monday of the Russians. In 1867, when the United States purchased Alaska from Russia, the date in use there was made to conform to that used in the United States.