In general, we may defend ourselves with the idea, that, if the Egyptians had possessed so long a series of observations, and of accurate observations too, their disciple Eudoxus, who studied among them for thirteen years, would, on his return, have brought into Greece a system of astronomy more perfect, and maps of the heavens less erroneous, and more coherent in their different parts.[193] How should it happen that the precession of the equinoxes was not known to the Greeks, but through the works of Hipparchus, if it had been marked in the registers of the Egyptians, and inscribed in characters so manifest upon the ceilings of their temples? And how comes it that Ptolemy, who wrote in Egypt, should not have deigned to avail himself of any of the observations of the Egyptians?[194] Farther, Herodotus, who lived so long with them, says nothing of those six hours which they added to the sacred year, nor of that great Sothian period which resulted. On the contrary, he says expressly that the Egyptians, making their year of 365 days, the seasons returned to the same point, so that in his time the necessity of this quarter of a day does not appear to have been suspected.[195] Thalles, who had visited the priests of Egypt, less than a century before Herodotus, did not, in like manner, make known to his countrymen, any other than a year of 365 days only.[196] And, if we reflect that all the colonies which migrated from Egypt, fourteen or fifteen centuries before Christ, the Jews and the Athenians, carried with them the lunar year, it will perhaps be inferred that the year of 365 days itself had not existed in Egypt in these remote ages. I am aware that Macrobius[197] gives the Egyptians a solar year of 365¼ days; but this author, who is comparatively modern, and who lived at a long period after the establishment of the fixed year of Alexandria, must have confounded the epochs. Diodorus[198] and Strabo[199] only attribute such a year to the Thebans; they do not say that it was in general use, and they themselves did not live till long after Herodotus. Thus the Sothian or great year must have been a comparatively recent invention, since it results from the comparison of the civil year with this pretended heliacal year of Sirius; and it is for this reason that it is only spoken of in the works of the second and third century after Christ[200], and that Syncellus alone, in the ninth, seems to cite Manetho as having made mention of it.