in Chronology, a series of seventy-five seventy-six years, perpetually recurring; which clasped, the middle of the new and full moons, as its inventor Calippus, an Athenian, imagined, return to the same day of the solar year. Meton, an hundred years before, had invented the period, or cycle, of nineteen years; assuming the quantity of the solar year $365\frac{1}{4}$ days, $6b. 18' 56'' 50^2$ $21' 34\frac{3}{4}$; and the lunar month, $29d. 12b. 45' 47'' 26\frac{1}{4} 48\frac{3}{4} 30\frac{3}{4}$; but Calippus, considering that the Metonic quantity of the solar year was not exact, multiplied Meton's period by 4, and thence arose a period of 76 years, called the Calippic. The Calippic period, therefore, contains 27,759 days: and since the lunar cycle contains 235 lunations, and the Calippic period is quadruple of this, it contains 940 lunations. This period began in the third year of the 112th Olympiad, or the 438th of the Julian period. It is demonstrated, however, that the Calippic period itself is not accurate; that it does not bring the new and full moons precisely to their places: $8b. 5' 52'' 60''$, being the excess of 940 lunations above 76 solar years; but brings them too late, by a whole day in 225 years.