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vernal equinox. And in order that this rulemight be properly observed, it became necessaryto know the days when the full moons wouldhappen, in the course of every year. But thiswas a knowledge that was not easily obtained;for the period formerly established by a Greekphilosopher of the name of Meton, which madenineteen years exactly equal to two hundred andthirty-five lunations, or revolutions of the moon,was found to be too long by about one hour andthirty-two minutes: and, consequently, aftersixteen of these periods, the true phases of themoon would precede those shown by the calen-dar, by more than a whole day.

At the time when the Gregorian account firsttook place, the error occasioned by this meansamounted to four days; and had the old methodof computation prevailed, the calendar, in time,would have announced the full moon at thetime of the change, and Easter would have beencelebrated at a period directly opposite to thatestablished by the church. To correct theseerrors, therefore, it was necessary that someother method should be devised, than that whichhad been hitherto in use; and as the old lunarcycle of nineteen years had a particular pro-perty, which had not yet been noticed, Luiliushad the good fortune to discover it, and tomake it subservient to the purposes required.

The