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The International Fixed calendar (also known as the Cotsworth plan, the Eastman plan, the 13 Month calendar or the Equal Month calendar) is a solar calendar proposal for calendar reform designed by Moses B. Cotsworth, who presented it in 1902.〔Moses B. Cotsworth, ''The rational almanac: tracing the evolution of modern almanacs from ancient ideas of time, and suggesting improvements'' (Acomb, England:Cotsworth, 1905)〕 It provides for a year of 13 months of 28 days each. It is therefore a perennial calendar, with every date fixed always on the same weekday. Though it was never officially adopted in any country, it was the official calendar of the Eastman Kodak Company from 1928 to 1989.〔Exhibit at George Eastman House, viewed June 2008〕 == Rules == The calendar year has 13 months with 28 days each, divided into exactly 4 weeks (13 × 28 = 364). An extra day added as a holiday at the end of the year (December 29), sometimes called "Year Day", does not belong to any week and brings the total to 365 days. Each year coincides with the corresponding Gregorian year, so January 1 in the Cotsworth calendar always falls on Gregorian January 1.〔See the table in Cotsworth, ''Rational Almanac'', p. i.〕 Twelve months are named and ordered the same as those of the Gregorian calendar, except that the extra month is inserted between June and July, and called ''Sol''. Situated in mid-summer (from the point of view of its Northern Hemisphere authors), the name of the new month was chosen in homage to the sun.〔Cotsworth suggested "Mid" as an alternative name. See his address in Royal Society of Canada, ''Proceedings and Transactions of the Royal Society of Canada,'' 3d series, vol. II (Ottawa: James Hope & Son, 1908), pp. 211-41 at 231.〕 Leap year in the International Fixed Calendar contains 366 days, and its occurrence follows the Gregorian rule. There is a leap year in every year whose number is divisible by 4, but not if the year number is divisible by 100, unless it is also divisible by 400. So although the year 2000 was a leap year, the years 1700, 1800, and 1900 were common years. The International Fixed Calendar inserts the extra day in leap year as June 29 - between Saturday June 28 and Sunday Sol 1. Each month begins on a Sunday, and ends on a Saturday; consequently, every year begins on Sunday. Neither Year Day nor Leap Day are considered to be part of any week; they are preceded by a Saturday and are followed by a Sunday. All the months look like this: The following shows how the 13 months and extra days of the International Fixed Calendar occur in relation to the dates of the Gregorian calendar: * 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「International Fixed Calendar」の詳細全文を読む スポンサード リンク
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