766 THE POPULAR SCIENCE MONTHLY, 



was appointed to give notice to the Pope, and other dignitaries in va- 

 rious parts of the Christian world, of the time when Easter should be 

 celebrated each year, until a perfectly correct cycle should be estab- 

 lished. The most prominent cycle framed for this purpose was one by 

 a mathematician named Victorinus. It consisted of the product of the 

 lunar and solar cycle i. e., 19 X 28 = 532. If this calculation had 

 been without defect, any given day would have been the same day of 

 the year, month, moon, and week, that it was five hundred and thirty- 

 two years before or would be five hundred and thirty-two years after. 



The Council of Orleans, a. d. 541, decreed that the feast of Easter 

 should be celebrated every year, according to the table of Victorinus. 

 But the tables derived from these data answer only for a limited time 

 on account of the above-mentioned errors in the year and in the lunar 

 cycle. Accordingly, the books which contain tables for finding Easter 

 are good only until the y6ar 1900, when new ones must be made for 

 another period. 



As the cycles were fixed by the Latin Chnrch, the era of Christ 

 began in the tenth year of the solar cycle and in the second year of 

 the lunar cycle. Therefore, to find what year of the solar cycle any 

 given year of our Lord is, we add 9 to the number of the year and di- 

 vide by 28 ; the remainder, if any, will indicate the number of the year 

 of the cycle. The year of the lunar cycle, i. e., the golden number, is 

 found in a similar manner, by adding 1 to the given year and dividing 

 by 19 ; the remainder will indicate the year of the lunar cycle. 



After the Julian calendar had been used several centuries, the im- 

 proved state of astronomy disclosed the fact that computed time did 

 not keep pace with actual time, because the year did not consist of 

 three hundred and sixty-five days ^nd six hours but was about eleven 

 minutes ten seconds less. Hence, by inserting an extra day for leap- 

 year, we gain upon true time forty-four minutes, forty seconds, which 

 makes an error of a day in about one hundred and thirty-one years ; 

 and hence, in 1582, when the correction of the calendar was undertaken 

 by Pope Gregory, the error had amounted to ten days ; i. e., instead of 

 counting just 1,582 years it ought to have been 1,582 years and ten 

 days. A correction was accordingly made by taking a leap of ten days 

 and calling October 5th of that year October 15th. This change, as 

 elsewhere stated, brought the vernal equinox to the 21st of March, where 

 it was at the time of the Nicene Council. To prevent the recurrence of 

 the same error in future, it was ordered that every fourth year should 

 be a leap-year as before, but centurial years, though multiples of 4, 

 should not be leap-years unless they were multiples of 400. The loss 

 of \\\ minutes yearly in time, as computed by the Julian method, 

 amounts in 100 years to 18*6 hours. Calling this one hundredth year 

 a common year gives a gain of one day, or 24 hours, which puts com- 

 puted time ahead of actual time, 24 18-6 = 5-4 hours, which, in 400 

 years, equals 21-6 hours, gain. Calling the four hundredth a leap- 



