110 ON THE REVOLUTIONS OF 



hundred and sixty-five days and a quarter, they imagined a period, 

 after which the tropical year, the ancient year, the year of the three 

 hundred and sixty-five days only, would revert to the same day ; a pe- 

 riod which, according to these incorrect data, was necessarily 1461 

 sacred years, and 1460 of those perfected years, to which they gave 

 the name of the years of Sirius. 



They took as the point of departure of this period, which they 

 called the sothaic or great year, a civil year ; the first day of which was 

 or had been also that of the soliacal rising of Sirius ; and we learn 

 from the positive testimony of Censorinus, that one of these great 

 years terminated in the year 138 before Christ.* Consequently it be- 

 gan 1322 years before Christ, and that which preceded it, 2782 years 

 previously. In fact, from calculations of M. Ideler, we learn that 

 Sirius rose heliacally on the 20th July, in the Julian year 139, a day 

 which corresponds to the first of Thot, or the first day of the sacred 

 Egyptian year.f 



But not only the sun's position, with relation to the stars of the 

 ecliptic or the sidereal year, is not the same as the tropical year, 

 because of the precision of the equinoxes. The heliacal year of 

 a star, or the period of its heliacal rising, especially when it is 

 distant from the eliptic, differs also from the sidereal year, and differs 

 variously, according to their latitudes in the places of observa- 

 tion, Yet what is singular enough, and what Bainbridge,j and 

 father Petau§ have remarked, || is, that it happens by a remarkable 

 concurrence in the positions, that in the latitude of Upper Egypt, at 

 a certain epoch, and during a certain number of centuries, the year 

 of Sirius, was really within very little of three hundred and sixty-five 

 days and a quarter ; so that the heliacal of this star returned, in fact, 

 to the same day of the Julian year, on the 20th of July, in 1322 years 

 before, and 138 after Christ.^ 



* All this system is developed by Censorinus, de Die Natali, cap, xviii. and xxi. 



-f- Tdeler. Hist. Researches on the Astronomical Observations of the Ancients. 

 Halma's translation at the end of his Canon of Ptolamseus, p. 32, et. seq. 



X Bainbridge, Canicul. 



§ Petau, Var. Diss. lib. v, c. vi, p. 108. 



II See La Nauze, on the Egyptian year. Acad, de Bell. Let. v. xiv. p. 346, and 

 the Memoir of Fourier, in the great work on Egypt, Mem. v. i, p. 803. 



^ Petau, loc. cit. M. Ideler affirms that this coincidence of the heliacal rising of 

 Sirius, tooh place also 2782 years before Christ, (Rech. Hist, in the Ptolemaeus of 

 M. Halma, v. iv, p. 37-) But mth respect to the Julian year, 1498 after Christ, 

 which is also the last of a great year, father Petau and M. Ideler differ. The latter 

 places the heliacal rising of Sirius, on the 22nd of July, the former on the 1 9th of 

 August. 



