Secret_History

434 The Secret History of the World
The role of Egyptian mathematics is probably best described as a retarding force
upon numerical procedures. Egyptian astronomy had much less influence on the
outside world for the very simple reason that it remained through all its history on
an exceedingly crude level which had practically no relations to the rapidly growing
mathematical astronomy of the Hellenistic age. Only in one point does the Egyptian
tradition show a very beneficial influence, that is, in the use of the Egyptian
calendar by the Hellenistic astronomers. This calendar is, indeed, the only
intelligent calendar which ever existed in human history. A year consists of 12
months of 30 days each and five additional days at the end of each year.
A second Egyptian contribution to astronomy is the division of the day into 24
hours, through these hours were originally not of even length, but were dependent
on the seasons. […]
Lunar calendars played a role since early times side by side with the schematic civil
calendar of the 365-day year. An inscription of the Middle Kingdom mentions
“great” and “small” years, and we know now that the “great” years were civil years
which contained 13 new moon festivals in contrast to the ordinary “small” years
with only 12 new moons. The way these intercalations were regulated, at least in
the latest period, is shown by the Demotic text.
This Demotic text contains a simple periodic scheme which is based on the fact that
25 Egyptian civil years (which contain 9125 days) are very nearly equal to 309
mean lunar months. These 309 months are grouped by our text into 16 ordinary
years of 12 lunar months, and 9 “great” years of 13 months. Ordinarily two
consecutive lunar months are given 59 days by our scheme, obviously because of
the fact that one lunar month is close to 29 " days long. But every 5 th year the two
last months are made 60 days long. This gives for the whole 25 year cycle the
correct total of 9125 days.
Since at this period all astronomical computations were carried out in the
sexagesimal system, at least as far as fractions are concerned, the equinoctial hours
were divided sexagesimally. Thus our present division of the day into 24 hours of
60 minutes each is the result of a Hellenistic modification of an Egyptian practice
combined with Babylonian numerical procedures.
Finally, we have to mention the decans. […] The decans are the actual reason for
the 12 division of the night and hence, in the last analysis, of the 24 hour system.
Again, in Hellenistic times the Egyptian decans were brought into a fixed relation
to the Babylonian zodiac which is attested in Egypt only since the reign of
Alexander’s successors. In this final version the 36 decans are simply the thirds of
the zodiacal signs, each decan representing 10 degrees of the ecliptic. Since the
same period witnesses the rapid development of astrology, the decans assumed an
important position in astrological lore and in kindred fields such as alchemy, the
magic of stones and plants and their use in medicine. In this disguise the decans
reached India, only to be returned in still more fantastic form to the Muslims and
the West. […]
[In the decans] we have not a calendar but a star clock. The user of this list would
know the hour of night by the rising of the decan which is listed in the proper
decade of the month. […]
We call this phenomenon the “heliacal rising” of S, using a term of Greek
astronomy. [...]