Adams, Walter M.: The house of the hidden places: a clue to the creed of early Egypt from Egyptian sources (London, 1895)

IV.] The Cycle of Sot his. 135

of the heavenly bodies, and occurring only
after long and clearly measured intervals.
Such an interval is afforded by the famous
Cycle of Sothis, of high antiquity in Egypt,
and peculiar to that country, the principle of
which, being dependent upon the relative
rates of the earth's rotation and revolution
respectively, has by no means been always
thoroughly understood.*

Since the average interval between two
successive risings of a given star at a particular
place is determined only by the period of the
earth's rotation, whereas in the case of the sun
a period of about four minutes must be added,
on account of the motion of revolution in her
orbit during that period, it follows, as we have
seen, that the star will on the average rise at
that place about four minutes earlier every
day, making the round of the twenty-four

* As, for instance, by the famous scholar Sealiger, whose
misunderstanding was exposed by Professor Greaves, the
Oxford astronomer, in A.r>. 1G40.