THE I> K T K R M I NATION OF K ASTER DAY. 



163 



corresponding to that employed in the arbitrary shifting of one of 

 the Golden Numbers, as already explained, to prevent the occur- 

 rence of two calendar full moons on the same date twice during 

 a single cycle. Such a collision would occur were twenty-five to 

 be used as the epact in this place of the cycle of epacts which is 

 at present applicable. This will he understood when it is 

 explained that, to obtain the date of the Paschal full moon from 

 the epact, it is necessary to subtract the amount of the latter 

 from April 13, or its equivalent, March 44. Since the epact is 

 the age of the moon on January 1, it is also the age of the 

 moon on March 31, and as the date of full moon is found by 

 adding thirl ecu days to that of new moon, the reason for the 

 rule is evident. The application of this rule gives the date of 

 the Paschal full moon directly if the epact is not greater than 

 twenty-three. But when the epact is twenty-four, or greater, the 

 number of days between the calendar full moons, with which 

 we are concerned, must be added to the date so found. Thus 

 when the epact is twenty-four, we find March 20 (by the sub- 

 traction from March 44), and must add twenty-nine days, which 

 brings us to April 18 as the date of the Paschal full moon. An 

 epacl of twenty-five, or greater, brings us, by the necessary 

 subtraction, to March 19, or earlier in March, as the case may be, 

 and then, in accordance with the convention already explained, 

 we must add thirty days to the date so found. The epact 

 twenty-five would, therefore, bring us again to April 18, but as 

 twenty-six is the value to be used, the adopted day of Paschal 

 full moon is, in this case, April 17. 



Although the explanation of these matters that has now been 

 given may appear tedious, and the rules complicated, still, as 

 was said at the beginning of the paper, once the requisite tables 

 are available, their application is extremely simple and easy. 

 Thus to find Easter Day in 1916 : We have seen already that 

 the Sunday Letters are BA ; the Golden Number is xvii ; the 

 epact is twenty-six. Opposite to xvii in the table of Golden 

 Numbers we find April 17, and the next Sunday is April 23. 

 Or, if we prefer to use the epact, subtraction of twenty-six 

 from March 44 gives March 18, the addition of thirty to this 

 brings us to April 17, and, as before, the next Sunday is 

 April 23. That is how to determine the date of Easter Day 

 in 1916. 



It will probably surprise those who have not considered the 

 matter to find how the dates of Easter sometimes diverge 

 widely according as we use the Julian or the Gregorian style 

 for the determination. 



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