This period of its career being accomplished, it began a second of equal length, then a third, and so on, in an infinite series, during which it traversed the same celestial houses and repeated in them the same acts of its life:  all the eclipses which it had undergone in one period would again afflict it in another, and would be manifest in the same places of the earth in the same order of time.* Whether they ascribed these eclipses to some mechanical cause, or regarded them as so many unfortunate attacks made upon Sin by the seven, they recognized their periodical character, and they were acquainted with the system of the two hundred and twenty-three lunations by which their occurrence and duration could be predicted.  Further observations encouraged the astronomers to endeavour to do for the sun what they had so successfully accomplished in regard to the moon.

* This period of two hundred and twenty-three lunations is that described by Ptolemy in the fourth book of his “Astronomy,” in which he deals with the average motion of the moon.  The Chaldaeans seem not to have been able to make a skilful use of it, for their books indicate the occurrence of lunar eclipses outside the predicted periods.

No long experience was needed to discover the fact that the majority of solar eclipses were followed some fourteen days and a half after by an eclipse of the moon; but they were unable to take sufficient advantage of this experience to predict with certainty the instant of a future eclipse of the sun, although they had been so struck with the connection of the two phenomena as to believe that they were in a position to announce it approximately.* They were frequently deceived in their predictions, and more than one eclipse which they had promised did not take place at the time expected:** but their successful prognostications were sufficiently frequent to console them for their failures, and to maintain the respect of the people and the rulers for their knowledge.  Their years were vague years of three hundred and sixty days.  The twelve equal months of which they were composed bore names which were borrowed, on the one hand, from events in civil life, such as “Simanu,” from the making of brick, and “Addaru,” from the sowing of seed, and, on the other, from mythological occurrences whose origin is still obscure, such as “Nisanu,” from the altar of Ea, and “Elul,” from a message of Ishtar.  The adjustment of this year to astronomical demands was roughly carried out by the addition of a month every six years, which was called a second Adar, Blul, or Nisan, according to the place in which it was intercalated.

* Tannery is of opinion that the Chaldaeans must have predicted eclipses of the sun by means of the period of two hundred and twenty-three lunations, and shows by what a simple means they could have arrived at it.

** An astronomer mentions, in the time of Assurbanipal, that on the 28th, 29th, and