SOTHIAC PERIOD. The ancient Egyptian year consisted only of 365 days, without any intercalation ; and was divided into 12 months of 30 days each, with 5 days added at the end. (I ferodotus, ii. 4.) The Scholiast on /tsetss informs us that the priests were sworn never to alter this year. This oath, we may conjecture, only came jute use after the discovery of the fact that a fraction of a day more would have been desirable to make the civil year conform to the suu. As long as 365 days was imagined to be the real year, it is not likely that they would hare sworn each ether to its observance; but if, after the discovery, a party were formed in favour of an alteration. the attempt to preserve the ancient institution by an oath would be almost a matter of course. Again, Diedorus Siculus (i. 50) says, that the Egyptians add five days and a quarter to the 360 days of their 12 months, which statement is generally supposed to refer to a more correct year which had been introduced among the people, while their religious festivals continued to be regulated by the old year. The propriety of this mode of reconciling the two authorities is made probable by the known existence of the Sothiac period (also called the Canicular year, Annus Magnus, &c., derived from Sothis, a name for the star Sirius) mentioned by Geminus, and also by Censorinus and Cletueut of Alexandria, from older writers. It is obvious that 1461 years of 365 days each make 1460 years of 365} days. This period of 1460 Julian years was the Sothiac period. It is impossible to fix any time at which this period was introduced, or to say whether, during its existence as a recognised cycle, it had time to run its whole career. Had it been a real cycle of experiment, it must be imagined that it would have been found to be wrong, to the extent of requiring an addition to the oath ; for 1503 real years is nearer to the time in which a year of 365 days would have its beginuing in all the seasons successively, and recommence the same process. It is obvious that such a cycle of recurrence was the intention
of the Egyptians in constructing the period : their vague year (annul rages) of 365 days, combined with their nearly fixed festivals, depend ing upon the heliacal rising of Status, made the latter take all conse cutive positions among the months of the former, gradually falling later and later. Again, if the Egyptians had really gone through a whole recorded period, it is difficult to see how they would avoid dis covering that another cycle would be necessary. In the time of their ancient kings the heliacal rising of Sirius would have advanced, by the precession of the equinoxes, about 12 days in one Sothiac period. The beginning of the vague year (365 days) was continually falling back ; so that if at the beginning of a,.period they had noted the day of their vague year on which the equirox fell, and also the day on which Sirius rose heliacally, they would have found that the latter came again to the same day of the vague year fifty years, or thereabouts, before the equinox was similarly restored. This, so far as the star was con cerned, would fit their erroneous period very well (1460 of 1505); but it is difficult to suppose that astronomers who had dis covered the odd quarter of a day which the year requires, should not know within 12 days the time of the equinox.
The epoch of commencement of a Sothiae period is not well deter mined and only from comparatively modern writers. Censorinus asserts that the consulship of Ulpius and Poutianus (usually placed in A.D. 238) was in the hundredth year of such a period : accordingly B.C. 1322 was the beginning of the preceding period. Clement of Alex andria says that the period began 345 years after the migration of the Israelites from Egypt, a date which differs considerably from that of Censorinus, according to modern chronologers. The point is however of no importance, as no dates were ever recorded in written history by means of Sothiae periods.