in chronology, a period of 76 years, continually recurring; at every repetition of which, it was supposed by its inventor Calippus, an Athenian astronomer, that the mean new and full moons would always return to the same day and hour.

About a century before, the golden number, or cycle of 19 years, had been invented by Meton; which Calippus finding to contain 19 of Nabonassar's year, 4 days, and $\frac{3}{5}$, to avoid fractions he quadrupled it, and so produced his period of 76 years, or 4 times 19; after which he supposed all the lunations, &c. would regularly return to the same hour. But neither is this exact, as it brings them too late by a whole day in 225 years.