“ PERIOD (Lat. periodus, from Gk. περίοδος, a going round, circumference, circuit, cycle, sentence, period, from περί, peri, around + ὁδός, hodos, road) . A term used in chronology in the same sense as cycle, to denote an interval of time after which the astronomical phenomena to which it refers recur in the same order. It is also employed to signify a cycle of cycles. The Chaldeans invented the Chaldaic period or Saros, from observing that, after a certain number of revolutions of the moon round the earth, her eclipses recurred in the same order and of the same magnitude. ”