67 L. Ideler, _Handbuch der mathematischen und technischen Chronologie_, i. 124 _sqq._; R. Lepsius, _Die Chronologie der Aegypter_, i. 168 _sq._; F. K. Ginzel, _Handbuch der mathematischen und technischen Chronologie_, i. 190 _sq._; Ed. Meyer, “Nachträge zur ägyptischen Chronologie,” _Abhandlungen der königl. Preuss. Akademie der Wissenschaften_, 1907 (Berlin, 1908), pp. 11 _sq._; _id._, _Geschichte des Altertums_,2 i. 28 _sq._, 99 _sqq._ The coincidence of the rising of Sirius with the swelling of the Nile is mentioned by Tibullus (i. 7. 21 _sq._) and Aelian (_De natura animalium_, x. 45). In later times, as a consequence of the precession of the equinoxes, the rising of Sirius gradually diverged from the summer solstice, falling later and later in the solar year. In the sixteenth and fifteenth century B.C. Sirius rose seventeen days after the summer solstice, and at the date of the Canopic decree (238 B.C.) it rose a whole month after the first swelling of the Nile. See L. Ideler, _op. cit._ i. 130; F. K. Ginzel, _op. cit._ i. 190; Ed. Meyer, “Nachträge zur ägyptischen Chronologie,” pp. 11 _sq._ According to Censorinus (_De die natali_, xxi. 10), Sirius regularly rose in Egypt on the twentieth of July (Julian calendar); and this was true of latitude 30° in Egypt (the latitude nearly of Heliopolis and Memphis) for about three thousand years of Egyptian history. See L. Ideler, _op. cit._ i. 128-130. But the date of the rising of the star is not the same throughout Egypt; it varies with the latitude, and the variation within the limits of Egypt amounts to seven days or more. Roughly speaking, Sirius rises nearly a whole day earlier for each degree of latitude you go south. Thus, whereas near Alexandria in the north Sirius does not rise till the twenty-second of July, at Syene in the south it rises on the sixteenth of July. See R. Lepsius, _op. cit._ i. 168 _sq._; F. K. Ginzel, _op. cit._ i. 182 _sq._ Now it is to be remembered that the rising of the Nile, as well as the rising of Sirius, is observed earlier and earlier the further south you go. The coincident variation of the two phenomena could hardly fail to confirm the Egyptians in their belief of a natural or supernatural connexion between them.