CHRONOLOGY. 
of dividing the flay have been in use among 
dift'erent nations ; but that which is now 
most general in civilized countries is into 
twenty-four equal parts or hours. With 
respect to the different inventions which 
have been used for measuring, or distin- 
guishing the hours of the day, we refer to 
tlie articles Clepsydra, Clock, Sun- 
Dial, &c. 
The Week, is a division of time of 
which it may be proper to take some 
notice before we proceed to the month. 
Various divisions which might be included 
under this denomination have obtained 
in different countries. The eailier Greeks 
divided their montli into three por- 
tions of ten days each: the Northern 
Chinese had a week of fifteen days, and the 
Mexicans one of thirteen. But the Chal- 
daeans, and most other Oriental nations, 
have, from time immemorial, used the Jew- 
ish week of seven days, which has been 
adopted by the Mahommedans, and intro- 
duced, with Christianity, to most of the 
civilized nations of the world. In the Old 
Testament the term week is occasionally 
applied to a period of seven years, as well 
as of seven days ; and to this it is necessary 
to attend, in order to understand the pas- 
sages wherein the word is used in that sense. 
The Month. There can be little doubt, 
but that tills division of time was at first 
suggested by tlie phases, or the periodical 
change in the appearances of the moon, 
and consequently, that in ancient compu- 
tations the months were invai-iably lunar. 
The difficulty, however, of adjusting this 
month to the annual revolution of the earth, 
led, with the improvement of astronomy, 
to the invention of other divisions under 
this name. Months are now divided into 
astronomical and civil. The astronomical 
months with which chronology is concern- 
ed, are measured by the revolutions of the 
moon, and are either periodical or syno- 
dical. The periodical lunar month is com- 
posed of the time which elapses between 
the departure of the moon from any part 
of her orbit, and her return to the same 
point, which is 27 days, 7 hours, and 43 
minutes. The synodical lunar montli is 
reckoned from one conjunction of the sun 
with the moon to another. This period is 
not always the same, being subject to the 
variation occasioned by the motion of the sun 
eastward on the ecliptic : a mean lunation 
consists of 29 days, 12 hours, and 44 minutes. 
This was tlie lunar montli mostly in use 
in ancient times. The civil month is that 
artificial space of time, by means of which 
the solar year is divided into twelve parts ; 
these months, which were first ordained by 
Julius Cassar, consist of thirty, or thirty- 
one days each, with the exception of Fe- 
bruary, which commonly contains twenty- 
eight, and every fourth year twenty-nine, 
days. 
Years. The year may be tenned the 
largest natural division of time. As the 
diurnal revolution of the earth would na- 
turally lead to the division into days, and 
the phases of the moon, with a little atten- 
tion, to that into months, so the annual 
motion of the earth round the sun, which 
would be marked by the periodical return 
of certain appearances, seasons, &c. would 
in due course lead to the adoption of tliis 
larger division. At what time this took 
place is uncertain, but probably not before 
considerable advances had been made in 
astronomical science. It was long, how- 
ever, after its first adoption, before it at- 
tained to any thing tike an accurate form. 
The most ancient measure of the year of 
which we know, consisted of twelve lunar 
months, which, for the facility of computa- 
tion, being all considered as equal in length, 
and to contain thirty days each, amounted 
to 360 days. It is conjectured that tliis 
gave rise to the division of the ecliptic, 
which still obtains, into 360 equal parts or 
degrees. 
This luni-solar year probably bad its rise 
in Chaldaea, or Egypt ; we learn, at least, 
from the testimony of Herodotus, that it 
was used in the latter country. Hence, 
with the diffusion of science, it was carried 
into other regions, and very generally 
adopted. It was early in use among the 
Indians, Chinese, the Medes, and Persians, 
and the ancient Greeks. Its measure 
being, however, inaccurate, containing five 
days and a quarter more tlian the lunar, 
and as much less than the true solar year, 
and this defect becoming every year more 
perceptible from the retrocession of tlie 
seasons, &c. it was soon considered neces- 
sary to subject it to some revision. The 
Thebans are supposed to have been the 
firet who undertook its correction, by mak- 
ing an annual addition of five days to the 
luni-solar year. Thales introduced this im- 
provement into the ancient Grecian year, 
and it was adopted, witli some trifling va- 
riations in particular instances, into the 
Indian, the Chinese, and tlie Jewish year. 
The Roman year, as regulated by Ro- 
mulus, and afterward reformed by his sue- 
