C H R O N 
of the fun and moon, combined with calculatidns of the 
years and eras of different nations. 2d. The teftimonies 
of credible, authentic, and unimpeached, authors. 3d. 
Such epochs in hiltory as are fo well attefted and deter¬ 
mined, that they have never been controverted. 4th. An¬ 
cient medals, coins, monuments, and inlcriptions; which 
ferve in general as fo many land-marks to regulate fur¬ 
ther enquiries. 
The moll obvious divifion of time, in all ages and 
countries, is to be referred to the apparent or real revo¬ 
lutions of the fun and moon. Thus, the apparent revo¬ 
lution of the fun, or the real rotation of the earth on her 
axis caufing the fun to appear to rife and let, conftitutes 
the vicilfitudes of day and night, which mult be evident 
to the moll barbarous and ignorant nations. The moon, 
by her revolution about the earth, and her changes, as 
naturally and obvioully forms months; while the great 
annual courfe of the fun through the feveral conllellations 
ot the zodiac, points out the larger divilion of the year. 
Of the COMMON DIVISIONS of TIME. 
Time itfelf is only a fuccelfion of phenomena in the 
univerfe; or a mode of duration marked by certain pe¬ 
riods. “ Our idea of time in general,” fays Mr. Locke, 
“ is formed by confidering any part of infinite duration, 
as fet out by periodical meafures : the idea of any parti¬ 
cular time, or length of duration, we acquire firft by ob- 
ferving certain appearances at regular and feemingly equi- 
dillant periods. Thus, by being able to repeat thefe lengths 
or meafures of time as often as we will, we can imagine 
duration, where nothing really endures or exifts; and 
hence we imagine to-morrow, or next year,” &c. Some 
philofophers define time to be, the duration of a thing 
whofe exiftence is neither without beginning nor end ; 
and .by this,, time is diftinguifhed from eternity. The moll 
familiar portions or meafures of time, are its fubdivifions 
into hours, days, weeks, months, and years ; but as thefe 
have varied confiderably in different ages and countries, 
it becomes the bufinefs of chronology to invelligate and 
explain them. 
An hour, is the aliquot part of a natural day, ufually 
the twenty-fourth, but fometimes a twelfth part. With 
us, it is the twenty-fourth part of the earth’s diurnal ro¬ 
tation, or the time from noon to noon, and therefore it 
anfwers to fifteen degrees of the whole circle of longitude, 
or of 360 degrees. The hour is divided by fixtieths, viz. 
firft into lixty minutes, then each minute into fixty feconds, 
&c. The divifion of time into hours is very ancient; as 
is Ihewn by Kircher, CEdip. ./Egypt, tom. 2. part. 2. The 
moll ancient hour is that of the twelfth part of the day. 
Herodotus obferves, that the Greeks learnt from the 
Egyptians, among other things, the method of dividing 
the day into twelve parts; and the aftronomers of Ca- 
thaya ftill retain this method. The divifion of the day 
into twenty-four hours, was not known to the Romans 
before the Punic war. Till that time they only regulated 
their days by the rifing and fetting of the fun. They di¬ 
vided the twelve hours of their day into four; viz. prime, 
which commenced at fix o’clock; third at nine; fixth at 
twelve, and none at three. They alfo divided the night 
into four watches, each containing three hours. 
Sometimes hours are divided into equal and unequal. 
Equal hours, are the twenty-fourth parts of a day and night 
precifely ; that is, the time in which the fifteen degrees of 
the equator pafs the meridian. Thefe are alfo called equi¬ 
noctial hours, becaufe mealured on the equinoctial; and 
aftronomical, becaufe ufed by aftronomers.— Agronomical 
hours, are equal hours, reckoned from noon to noon, in a 
continued ieries of twenty-four. —Babylonifh hours, are 
equal hours, reckoned from fun-rife in a continued feries 
of twenty-four.— European hours, ufed in civil computa¬ 
tion, are equal hours, reckoned from midnight; twelve 
from thence till noon, and twelve more from noon till mid¬ 
night.— Je'wiJb, or planetary, or ancient hours, are twelfth 
parts of the artificial day and night, They are called an- 
Vol. IV. No. 217. 
O L O G Y. 533 
cient or Jewilh hours, becaufe ufed by the ancients, and 
ftill among the Jew's. They are called planetary hours, 
becaufe the altrologers pretend, that a new planet comes 
to predominate every hour; and that the day takes its 
denomination from that which predominates the firft hour 
of it; as Monday from the moon, &c.— Italian hours, are 
equal hours, reckoned from fun-fet, in a continued feries 
of twenty-four.— Unequal or temporary hours , are twelfth 
parts of the artificial day and night. The obliquity of 
the fphere renders thefe more or lefs unequal at different 
times; fo that they only agree w'ith the equal hours at 
the times of the equinoxes. 
The next meafure of time above or fuperior to the 
hour, is that of the day, which is either natural, or arti¬ 
ficial. The artificial day is that which is primarily meant 
by the word day, and is the time of its being light, or the 
time while the fun is above the horizon. Though fome¬ 
times the twilight is included in the term day-light; in 
oppofition to night or darknefs, being the time from the 
end of twilight to the beginning of day-light. The na¬ 
tural day is the portion of time in which the earth makes 
a rotation on its axis. And this is either aftronomical, 
or civil. Afironomical day begins at noon, or when the 
fun’s center is on the meridian, and is counted twenty- 
four hours to the following noon. Civil day is the time 
allotted for day in civil purpofes, and begins differently 
in different nations, but ftill including one whole rota¬ 
tion of the earth on its axis; beginning either at fun-rife, 
fun-fet, noon, or midnight, ift. At fun-riling, among the 
ancient Babylonians, Perfians, Syrians, and moll other 
eaftern nations, with the prefent inhabitants of the Balea¬ 
ric iflands, the Greeks, See. 2dly. At fun-fetting, among 
the ancient Athenians and Jews, with the Aultrians, Bo¬ 
hemians, Marcomanni, Silefians', and modern Italians. 
3dly. At noon, with aftronomers, and the ancient Umbri 
and Arabians. And, xthly, at midnight, among the Egyp¬ 
tians, Chinefe, and Romans, with the modern Englilh, 
French, Dutch, Germans, Spaniards, and Portuguefe. 
The different length of the natural day in different cli¬ 
mates, has been matter of controverfy, viz. whether the 
natural days be all equally long throughout the year; and 
if not, w'hat their difference is ? A profeffor of mathema¬ 
tics at Seville, in the Philof. Tranf. vol. x. p. 425/afferts, 
from a continued feries of obfervations for three years, 
that they are all equal. But Mr. Flamfteed, in the fame 
Tranf. p.429. refutes the opinion; and fhews that one 
day, when the fun is in the equinoctial, is ihorter than 
when he is in the tropics, by forty feconds; and that 
fourteen tropical days are longer than fo many equinoftial 
ones, by ten minutes. This inequality of the days flows 
from two diftinft principles: the one, the eccentricity of 
the earth’s orbit; the other, the obliquity of the ecliptic 
with regard to the equator, which is the true meafure of 
time: but as thefe two caufes happen to be differently 
combined, the length of the day is varied. 
The next divifion of time beyond the day, is that of 
weeks, which comprifes feven days. The origin of this 
divifion, or of computing time by fevenths, is much con¬ 
troverted. It has often been thought to have taken its 
rife from the four quarters or intervals of the moon, be¬ 
tween her changes of phafes, which, being about feven 
days diftant, gave occafion to the divifion : but others 
more probably, from the feven planets. Be this as it may, 
the divifion is certainly very ancient. The Syrians, 
Egyptians, and moll of the oriental nations, appear to 
have ufed it from the earliefl ages: though it did not get 
footing in the weft till brought in by Chriftianity. The 
Romans reckoned their days not by fevenths, but by 
ninths ; and the ancient Greeks by decads, or tenths ; in 
imitation of which the new French calendar feems to have 
been framed. The Jews divided their time by weeks, of 
feven days each, as preferibed by the law of Moles; in 
which they were appointed to work fix days, and to rell 
the feventh, in commemoration of the creation. This 
method was in ufe in the days of Hefiod 5 but it was not 
6 U until 
