INTRODUCTION 9 



this science was put. The same distinctive feature 

 appears again in astronomy. 



2. THE ASTRONOMICAL SCIENCES 



In connection with the annual risings of the Nile, the 

 Egyptians attached great importance to the exact 

 determination of the periodic return of the seasons, 

 and the religious festivals held in its celebration ; and 

 their observations relating to the measurement of time 

 were far advanced. 



As far back as we go in the history of Egypt, we see 

 that the year was always divided into 12 months of 30 

 days each, plus 5 supplementary days ; but it is prob- 

 able that originally the year had only 360 days, if the 

 following tradition, reported by Plutarch, is to be be- 

 lieved : x Saturn having secretly wedded Rhea, the 

 Sun forbade her to give birth either during the course 

 of a month or of a year. Hermes, the devoted servant 

 of the goddess, played at dice with the Moon and gained 

 from her the 72nd part of each day ; thus a total of 

 5 supplementary days was provided during which Rhea 

 might bring her child into the world. 



The Egyptians had therefore ascertained, at a very 

 remote epoch, that the period of 360 days for a year is 

 too short. They recognized also that 365 days is not 

 enough, and must be extended to 365J days. For if 

 once the sun rose at the same time as Sirius on the 

 first day of the year, the following year at the same 

 period, Sirius would rise six hours later than the sun, 

 and at the end of four years one day later. Thus, 

 there would have to be 365 x 4 = 1,460 years before 

 the risings of the sun and Sirius coincided again on the 

 first day of the year. This period of 1,460 years is the 

 celebrated Sothiac period (Sothis being the Egyptian 

 name for Sirius) which regulated the celebration of 



1 De I side et Osiride, ch. 22 (18 Maspero, Histoire Ancienne, 

 p. 80). 



