INTERNATIONAL DATE-LINE. An ir regula• line drawn somewhat arbitrarily on the inap of the Pacific Ocean, near the ISO' meridian of longitude. It marks the place where oat iga to•s 'change their date' on the trans-Paeitie voy age. The following is a brief explanation of the cause of this change of date. When a person travels west ward, he lengthens his day by one hour for every 15 degrees, since he moves along with the motion of the sun ; by going westward entirely round the earth, lengthening each day by a cer tain amount, four minutes for every terrestrial degree lie travels, he will have lost one day at the arrival at the starting-point. The second of a month, for example, is to him the first ; Monday is Sunday. according to his reckoning. This is obvious, since by going round the earth from east to west lie has, in respect to himself. diminished by one the number of revolutions made by the earth during this time. Going round the earth eastward the reverse takes plaee, and a person gains one day, since he makes one more revolution than the earth does. Thus two persons, having started from the same place and traveled round the earth in opposite directions, when they meet at their place of starting, will differ from each other two days in their reckoning. Thus it be comes necessary to have a dateline somewhere on the earth's surface, since it. is impossible that the reckoning of days should go unbroken round the earth. Any meridian might do, theoretically, for this purpose, hut for two important practical reasons the 180° meridian of longitude has been chosen for the international date-line. These two reasons are: (1) that it lies nearly in the mid dle of the Pacific Ocean, and thus far away from civilization: (2) it is exactly twelve hours from Greenwich, which is, however, of minor im portance. Thus the theoretical date-line coin cides with the 180° meridian; but for reasons of convenience an arbitrary irregular line has been adopted in its place. This line is shown on the
aceompanying map; it has the advantage that no change oeeurs between important neighboring islands.
Since the line is an arbitrary one. we mitdt expect. cartographic authorities to differ eon side•ahly in its delineation: and this is. in fact. I he ease. Indeed, to have ve such a line drawn with perfectly definite authority. it would be neees sa-y for the principal nations to have the line de termined by a joint commission, and then to adopt the commission's recommendations by inter national agreement or treaty. But this has never been done, and so in one sense it may be said there is no international dateline. The term has, however, come into general use, and may well be employed pending such governmental action. The matter might he dealt with very appropriately if there should ever he another Prime Meridian Conference (q.v.). But in the absence of international agreement., it is possible at least to mark out the line as it is actually used in the Pacific islands. For this purpose it is merely necessary to find out. by correspondence With ,111 the vuriuu. :4444ttlel0eatti, Whether date in public use i. the .1inerican ur .Asiatic tw. Correspondenct• of tItis kind has been carried on by I'D If.(;forge 1):10 i(1,1111, of the Cniversity of alifornia, and formerly of the United States I 'oast and (;eodet it. Survey. llis results have been published by the I 'tilted States I:overnitnt, mid form the basis of the accompanying map, which p•esents unquestionably the most authori tative date-line so far placed at our disposal. The principal change front other recent authorities transfers Alort•II Island to the east of the line. The change of the Samoan Islands from west to east was mode by order of King Alalietoa in I S92. See .1 NTIetams ; STANDARD.