Elementary arithmetic, with brief notices of its history... by Robert Potts.

12

ON THE DIVISIONS AND MEASURES OF TIME.

the completion of this period, the conjunctions, oppositions, and all
other aspects of the moon, would fall on the same days of each succeeding year as of the preceding nineteen years. As the solar year
did not contain an exact number of lunar months, he found out, 432
n.C., that by intercalating seven lunar months in nineteen lunar years
there would be 235 lunar months in nineteen solar years very nearly,
so that the times of celebrating the Grecian games and festivals
could be adjusted both to the new and full moons, and to the
equinoxes and solstices. It was afterwards discovered that, the moon
and the sun beginning to move from the same part of the heavens,
would not at the end of nineteen years be exactly together, but that
the moon would be in advance of the sun, and in 310 years the new
moon would appear at the end of this period one day in advance of
the time reckoned at the beginning of the succeeding period.
In order to remedy this discrepancy, Calippus, 330 B.C., proposed
four times nineteen years instead of nineteen years; but this amended
scheme did not completely bring the motions of the sun and the moon
into conformity. A small difference having been observed at the end
of this time, Hipparchus, 146 B.c., proposed a period of eight times
nineteen, or 152 years. And it may be remarked, that these three
astronomers in their successive attempts, approached nearer to success in adjusting the motions of the sun and the moon than any of
their predecessors.
The Olympic games were celebrated by the Hellenic people every
fourth year at Olympia, a city of Elis, on the banks of the Alpheus.
The time of the first institution of these games lies somewhere in the
mythical period of history. These games, after some interruption,
were restored by Iphitus about 884 B.c., and celebrated every fourth
year at the time of full moon at the summer solstice (Pind. Ode iii.)
The interval of four years between two celebrations was called at
Olympiad. It was not, however, until long after this date, that
Olympiads were employed for arranging the dates of historical events.
When the Olympiads were adopted as a measure of time, the date of
the first Olympiad was reckoned from that year in which Cormebus was
victor, and its date is placed 108 years after the revival of the games
by Iphitus, which year corresponds to 776 B.c. Strabo writes that
the early historians of Greece were ill-informed and credulous; and it
is difficult to distinguish what is mythical from what is historical. It
was not until later times that any exact mode of fixing the order of
events by dates came into use.
The method of reckoning by generations and the succession of
kings was variable, and likely to lead into error, if the early Greek
historians wrote from tradition without any original records and
authentic memorials to guide them. In the poems of Homer and
iHesiod no allusions are made to Olympiads. In the histories of
iHerodotus and Thucydides, the dates of important events are not
fixed by reference to the Olympiads or to any other epoch; and even
after the use of these had been established, ancient writers appear
not to have been much guided by them, and consequently there is
room for doubt in their statements of the exact times when events
happened.
JDionysius of Halicarnassus observes that HIerodotus in his histories
has followed the order of events, but Thucydides, in his history of the
Peloponnesian war, the order of time; that while Thucydides has