'The Calendars and Chronology 9 the Pyramid of Khufu, a period has been reached when the picture passes from the conjectural to the factual. The astro- nomical science displayed by the reform of Imhotep accords well with the astronomical, geometric, and engineering science exhibited in the construction of the Great Pyramid. Clearly the critic of the 365^ days calendar year may have objected to the fact that the result was that the Set festival, i.e. the calendar New Year day, moved forward from the actual autumn equinox at the rate of about 3 days in 400 years. It was perhaps in order to meet that criticism that Imhotep invented a seasonal year which no doubt he thought was precisely 365^ days in length, that is, the same length as the calendar year. Actually the mean Sothic year at this epoch was nearly a minute longer than 365 J days; but the 372 years of records which alone can have been available to him would hardly exhibit the error. Nevertheless there was this small error. The reform of Imhotep must therefore be recognized as the first retrogression from the scientific calendars of 3141. * For the next 2,800 years the sliding and the Sothic calendars remained the principal calendars of Egypt, although, as stated above, we find traces of the Set calendar still in use in some temples as late as -the reign of Rameses II. At the Roman period the confusion of calendars had become so involved that it is impossible to sort them clearly. Records exist which show 5 or 6 New Year days. In addition to 1.1 of the sliding calendar and 1.1 Sothic are the present 'Night of the Drop' (June 18-19 Gregorian), a New Year of Horus, which was possibly a relic of the Samhain festival, and another New Year day in the 1 An interesting illustration of the dictum of Solomon is afforded by the last step in this scientific retrogression, namely the introduction of our present calendar by Pope Gregory IX in 1582. The same objection to the 365 J days calendar was then raised as in the days of Imhotep. Whereas, however, Imh6tep met it by fitting a year to the calendar, the method adopted by the Vatican was that of attempting to fit a calendar to the tropical year. It repre- sented the final degradation of the calendar of 3141.