[67] The modern Egyptians still hold to the old months for irrigation. 7 Taba = January 15, is commencement of wheat irrigation; 30 Misra is the last safe date for sowing maize in the Delta; 1st Tut is the date of regulating the bridges = September 8 in Upper Egypt. [68] "Histoire ancienne des Peuples de l'Orient," p. 72. [69] "Chronologie," i., p. 70. [70] _Op. cit._, p. 187. [71] Krall, _loc. cit._, p. 20. [72] Mommsen, "Chronologie," p. 258. [73] "Studien zur Geschichte der Alten Aegypten," I. Wien, 1881. [74] "Matériaux pour servir à la Reconstruction du Calendrier," p. 29. [75] "Aeg. Zeit.," 1886, p. 5, quoted by Krall. [76] It should be observed that a distinction is made between the Julian and the historical year. This comes from the fact that when astronomical phenomena are calculated for dates B.C., it must be remembered that chronologists are in the habit of designating by 1, or rather by-1, the first year which precedes the instant of time at which the chronological year commenced, while astronomers mark this year in their tables by 0. It follows, therefore, that the rank of any year B.C. is always marked by an additional unit in the chronological dates. For the Christian era, of course, chronologists and astronomers work in the same way. The following table, given by Biot, exhibits the connection between these two methods. In the latter Biot shows the leap-years marked B, and the corresponding years in the Scaligerian chronological period are also given. DATES OF JULIAN YEARS COMMENCING ON JANUARY 1. According to According to Corresponding Chronologists. Astronomers. years of the period of Scaliger. -6 -5 4708 -5B -4B 4709 ── ── ─── -4 -3 4710 -3 -2 4711 -2 -1 4712 -1B -0B 4713B Physical instant when the era commenced. +1 +1 4714 +2 +2 4715 +3 +3 4716 +4B +4B 4717B ── ── ─── +5 +5 4718 [77] _Loc. cit._, p. 29. [78] Probably too great a value by two or three days. [79] _Op. cit._, p. 48. [80] Goodwin has already asked, "Does the Smith Papyrus refer to some rectification of the calendar made in the fourth dynasty, similar to that made in Europe from the old to the new style?" Quoted by Riel, "Sonnen-und Sirius-Jahr," p. 361.