IV. NOTES
The Epact
Abba Demetrius computed that every nineteen solar
years equalled nineteen lunar years plus two hundred and
nine days (l9 x 11). Hence the Epact is a cycle of nineteen
Solar-Lunar years in which a leap year would be composed
of thirteen months. In its broad lines, the Epact can be
summed up as follows:
In the first solar year there would be 11 extra days.
In the second year there would be 22 extra days.
In the third year there would be 33 extra days.
The third lunar year would, therefore, be a leap year;
containing thirteen months plus three days. These would be
added to the succeeding year.
In the fourth solar year there would be 3 plus 11, or
14 extra days.
In the fifth year there would be 25 extra days.
Therefore the fifth lunar year would be a leap year by
borrowing five days from the succeeding year.
The sixth solar year would have 11 minus 5, or 6
extra days.
The seventh year would have 6 plus 11, or 17 extra
days.
The eighth year would have 28 extra days.
Therefore, the eighth lunar year would be a leap year
by borrowing two days from the succeeding year.
In the ninth solar year there would be 11 minus two,
or 9 extra days.
In the tenth year there would be 9 plus 11, or 20
extra days.