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

6

ON THE DIVISIONS AND MEASURES OF TIME.

the sixth hour (John xix. 14), and the twelfth hour ended at
sunset. The third hour divided the interval between sunrise and
noon (Mark xv. 25), and the ninth hour between noon and sunset
(Matt. xxvii. 45). The two intermediate points of time which
equally divided the periods of light and darkness were noon and
midnight.
The month having been defined to be the time in which the moon
was observed to pass through its changes, is in fact the period during
which the moon completes one revolution in its own orbit round the
earth, and is at the same time carried with the earth in its orbit
round the sun. As the moon receives its light from the sun in
the same manner as the earth, the appearance of the new moon
will take place when the dark side of the moon is turned towards the
earth, or, more correctly, when the moon and the sun are in con2junction, or on the same side of the earth. And the full moon will happen
when the moon and the sun are in opposition, or on different sides of
the earth. On the second day after the conjunction the new moon is
first seen as a thin curved line of light, as part of a circular arc; but
the actual fact of conjunction can only be seen when the conjunction
is so close as to occasion an eclipse of the sun. In early times the
interval between two successive new moons was observed to be about
thirty days, and this period was reckoned the length of the month,
until more accurate observations showed that the exact time between
two new moons was less than thirty but more than twenty-nine days.
At length in modern times it was found that the average interval between
two successive new moons is 29 days, 12 hours, 44 minutes, and 3.
seconds; and the average interval from new moon to full moon is 14
days, 18 hours, 22 minutes, and 1 — second; and the full moon will,
therefore, generally happen on the 14th or 15th day of the moon's age.
The natural day, the lunar month, and the solar year are fixed,
but incommensurable with each other; thus, if the year be measured
by days, it contains more than 365, but less than 366 days; if
by lunar months, it contains more than 12 but less than 13; and if
the lunar month be measured by days it contains more than 29 but
less than 30 days.
In addition to the three natural divisions of time, the year, the
month, and the day, the most ancient of the artificial divisions of time
is the week, a period of seven days.1 The origin of this division of time
1 The period of seven clays, the seventh day, and the number seven, are foun(l
in the traditions and languages of almost all nations, fragments of the original
institution of the seventh day. It is not improbable that the name of the practice
of an observance might remain among a people long after the original tradition had
been lost, and any superstition might become connected with the name. The
ancient Egyptians celebrated the festival of their god Apis for seven days. The
time of six times seven days was the period of mortification imposed on the Egyptian
priests. And their custom of mourning for the dead was extended to ten times seven
days. It is recorded (Numb. xxiii. 1, 2) that Balak, the king of Moab, offered, by
the direction of Balaam, seven oxen and seven rams upon seven altars. And in a
later age, the Syrian general Naaman was directed by the Hebrew prophet Elisha to
wash seven times in the river Jordan for the cure of his leprosy (2 Kings v. 10).
In a still later age, the most ancient writers of the Greeks recognised the sanctity
of the seventh day of the month. Thus Hesiod calls " the seventh day the illustrious
light of the sun." And Homer writes:-"Then came the seventh day, which is a
sacred day." And Varro, in his book inscribed Hlebdomades, observes that he had then
entered upon the twelfth week of his years. It would be easy to multiply instances
of the use of the number seven among peoples separated from the Hebrew nation.
The tradition can only be referred to the primeval institution of the seventh day.