164 



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



The following comparison of dates for a few years will serve 

 as an illustration. 



Year. Eastern Church. Western Church. 



Old Style. New Style. 



1913 April 14 April 27 March 23 



1914 „ 6 „ 19 April 12 



1915 March 22 „ 4 4 



1916 April 10 „ 23 „ 23 



1917 „ 2 „ 15 „ 8 



The equivalent new style date is added, in the case of the 

 Eastern Church dates, for convenience of comparison with the 

 Western Church dates. It is quite unusual for Easter Day in 

 the two systems to occur on the same day in two consecutive 

 years as they do in 1915 and 1916. 



It will be understood that the various corrections and readjust- 

 ments that have been enumerated are for the purpose of pre- 

 serving a near agreement between the phases of the calendar 

 moon and those of the real moon. The difference is seldom 

 more than two or three days at most. But it is remarkable 

 that, in some critical cases near the Paschal Limits, a difference 

 of a few hours in the times of the phases sometimes makes a 

 large difference in the date of Easter, according as we rely on 

 the real or the calendar moon for the determination. Such a 

 case occurred in 1905, to which it may be of interest to refer. 

 In that year the real moon of the heavens was full at 4 hours 

 56 minutes Greenwich mean time on the morning of March 21. 

 Therefore, if we were to depend on the real moon, Easter Day 

 would have fallen on the following Sunday, March 26. But, 

 actually, Easter Day in that year fell on April 23, because 

 the calendar moon was full on March 20, and again on 

 April 18 ; the latter date, therefore — that of the Paschal 

 full moon of the calendar — causing Easter Day to fall on the 

 following Sunday, April 23. In this instance the dates thus 

 differ by four weeks according as we take the real or the 

 calendar moon for our guide in determining them. 



The adoption of the calendar moon for such purposes as 

 fixing the date of Easter has certain practical advantages, such 

 as applicability to every terrestrial longitude, that would not 

 be present in the case of the actual moon. Thus, in the 

 instance quoted above, in which the real moon is full at 

 4 hours 56 minutes Greenwich mean time on the morning of 



