in Chronology, a series of seventy-six CALIPPIAN period. Calippus, an Athenian, imagined, return to the same day of the solar year. Meton, a hundred years before, had invented the period, or cycle, of nineteen years; assuming the quantity of the solar year $365\frac{1}{4}$ days, $18^h 56' 50''$ $41^m 34^s$; and the lunar month, $29^d 12^h 45' 47''$ $26^m 48^s 30^s$. 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 4384th 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; $8^h 5' 52'' 60''$, being the excess of $940$ lunations, above $76$ solar years; but brings them too late, by a whole day in $225$ years.