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A. M. W. DOWNING. M.A., D.SC, F.R.S., ON 



real moon of the heavens, but the artificial moon of the 

 calendar, which, as we shall see later on, is regulated by certain 

 definite rules by means of which its phases are made to agree 

 pretty accurately with those of the real moon. This artificial 

 calendar moon is accounted to be " full " on the fourteenth day, 

 i.e., thirteen days after the new moon : an artifice suggested 

 by the practice prevalent amongst the Jews in early times of 

 counting the " new " moon from the time of first visibility of 

 the crescent, and considering it to be " full " on the following 

 fourteenth day. This artifice secures an approximate agreement 

 between the times of " full " (but not between the times of 

 " new " ) for the calendar moon and the real moon of the heavens. 



The decision of the Council of Mcaea, with regard to the 

 celebration of Easter, ended what is known as the Paschal 

 controversy, which had disturbed the Church for a great many 

 years previously. Certain Asiatic Christians kept their Paschal 

 solemnities on Nisan 14, and do not appear to have paid any 

 particular attention to the following Sunday, as a commemora- 

 tion of our Lord's Besurrection, except on those occasions 

 on which it happened to be the " third day." The Jews, 

 it will be remembered, killed the Paschal lamb on the 

 fourteenth day of the first month, or Xisan 14, " between 

 the evenings." It was then eaten during the following night, 

 which would be the commencement of the day Xisan 15, 

 according to the Jewish method of reckoning days. On 

 account of their practice in this respect, these Asiatic 

 Christians were called " Quartodecimans," and it is stated that 

 they claimed the sanction of St. John the Apostle as their 

 authority for their mode of celebrating Easter. On the other 

 hand the Western Churches, from very early times, made the 

 Sunday following Nisan 14 to be the central and chief day of 

 the Easter solemnities, which for them lasted an entire week. 



The Council of Nicaea decreed, then, that Easter Day should 

 be a Sunday having a certain position with regard to the vernal 

 equinox (then assumed to fall on March 21) and a certain 

 position with regard to a specified full moon. This involves a 

 consideration of three incommensurable quantities, the tropical 

 year, the week, and the lunar month, which necessarily 

 entails a considerable amount of complication. We shall find, 

 however, that once the requisite tables are constructed, the 

 process of finding the date of Easter is a perfectly simple one. 



And first, with regard to the tropical year. The old style or 

 Julian year was introduced by Julius Caesar, with the assistance 

 of Sosigenes, an astronomer of Alexandria, and is perhaps one 



