THE DETERMINATION OF EASTER DAY. 1G1 



in the three successive periods mentioned above, will show 

 clearly the manner in which the Numbers are shifted relatively 

 to the differenl days comprised within the Paschal Limits. It 

 will be noticed, for instance, that no Golden Number appears 

 opposite to March 21 during the period 1900 to 2199. This 

 means that no calendar full moon occurs on that day, and, 

 therefore, that Easter Day cannot fall as early as March 22 

 during this period. A consideration of the Numbers affixed to 

 April 17 and 18, during the successive periods, is very instruc- 

 tive, as exemplifying one of the peculiar artifices of which the 

 framers of the calendar appear to be so fond. It will be 

 observed that the Golden Numbers xvii and vi have not been 

 shifted in passing from 1899 to 1900, although all the 

 preceding Numbers have been brought down one day later in 

 the series. Now the calendar lunations consist generally of 

 thirty or twenty-nine days alternately, with certain modifications. 

 In general, if a lunation terminates in January or March it is 

 made to consist of thirty days, but if in February or April it is 

 to consist of twenty-nine days. But a special rule is made for the 

 particular case where a calendar full moon falls on either 

 March 19 or 20. It is assumed that if a full moon falls on 

 March 19, or earlier in March, then the April full moon will 

 fall thirty days later. But if the March full moon is on the 

 20th, the April full moon will happen twenty-nine days 

 later. Thus the calendar full moon of April will fall on the 

 same day (April 18) whether the March full moon happens 

 on the 19th or 20th of that month. To apply this to the 

 particular case before us, it will be seen that during the period 

 1700 to 1899, the Golden Number vi is affixed to April 18, and 

 that in the preceding lunation it would be affixed to March 19 

 (being two days earlier than the date to which xiv is affixed), 

 thus giving an interval of thirty days in length. But during 

 the period 1900 to 2199, the Golden Number vi is still affixed 

 to April 18, although in the preceding lunation it would now be 

 affixed to March 20. The interval, therefore, is, in this case, 

 only twenty-nine days in length, in accordance with the artifice 

 to which reference has been made. The framers of the calendar 

 further determined that two full moons must not occur on the 

 same date twice in a single nineteen-year period. And to avoid 

 such a contingency, the device was adopted of putting back the 

 date of a calendar full moon one day, when otherwise two 

 full moons would fall on the same date ; Golden Number xvii, 

 which would otherwise have been affixed to April 18 during the 

 period 1900 to 2199, is, therefore, put back to April 17, thus 



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