"Hesvan (Heshwan) or subtracted from the month Kislev (Kislew), as need arose, in order to keep the months in agreement with the moon; secondly, eight years out of every nineteen were made "embolismic", i.e. an intercalary month seems to have been introduced when necessary, at this point, in order to prevent the 14th day of Nisan from arriving too early."