Egyptian Chronology. 461 



at the higher parts of the stream, and hence it is unnecessary 

 that the astronomic forerunner should be actually prior to the 

 beginning of the inundation. This is more particularly the 

 case in central and lower Egypt, where, even if the rising of 

 Sirius did correspond with the first swell of the Nile on the 

 frontiers of Nubia, some days must elapse before the connexion 

 would be detected. 



We may, therefore, consider that we are warranted in 

 ascribing to a system, in which the two appearances, however 

 dissimilar in cause, were considered as identical in point of 

 time, an origin no farther distant than the period in which 

 they were actually contemporaneous. The rise of the Nile, 

 growing out of the tropical rains, follows in its law the tropical 

 year, and recurs, on an average, on a fixed day of our 

 present calendar. The heliacal rising of a star, on the other 

 hand, is affected by the precession of the equinoxes, and, in 

 consequence, recurs later every year than it did the preceding. 

 But it is not governed by the sidereal year exactly ; for, as the 

 declination of stars alters, as well as their right ascension, the 

 interval between the successive risings of the same star will not 

 have a constant length corresponding to the last named period ; 

 but it will vary, being sometimes longer, and sometimes 

 shorter; in respect to Sirius, this interval, as we ascertain 

 from the calculations of Larcher, which have been confirmed 

 by Biot, was, for from twenty to thirty centuries before the 

 Christian era, exactly 365J days, being greater than the 

 tropical, and less than the sidereal year. The difference, then, 

 between the real length of the year marked by the star, and 

 that determined by the rising of the Nile, will be the same as 

 that known to exist between the Gregorian and Julian calen- 

 dars, or three days in 400 years. 



Now, the rising of the Nile below the cataracts, although 

 usually referred to the solstice, actually occurs, at the isle of 

 Philae, at an average, on the 25th of June. This, therefore, is 

 the earliest day to which we are warranted in referring the 

 observation of the rising of Sirius, upon which the coincidence 

 of the two phenomena is founded ; while we are almost autho- 

 rised to place it even later, as the star would otherwise have 

 been seen at Thebes or This, before the increase of the Nile 

 could have been perceptible. 



