CHRONOLOGY. 
foal, placed within another of porcelain. It 
is thus reduced to the metallic state. It is 
to this chemist that we are indebted prin- 
cipally for a knowledge of its properties. 
Chrome is of a white colour, inclining to 
grey ; it is very brittle ; its fracture pre- 
sents a radiated appearance, needles crossing 
in different directions with interstices be- 
tween them. Its other physical qualities 
have not been determined. This metal is 
difficult of fusion. Exposed to the heat of 
the blow-pipe it does not melt. When 
fused by having been exposed to the in- 
tense heat necessary to its reduction, it 
presents crystalline filaments, which rise 
above the metallic mass. Chrome is not 
easily acted on by the acids. Even when 
reduced to a fine powder, and treated with 
concentrated boiling nitric acid, it is 
oxydized with much difficulty, and commu- 
nicates to the acid only a green tinge. 
Chrome, in the state of acid, appears to 
be more susceptible of combination, and 
this acid being obtained without difficulty 
from its native combinations, its chemical 
relations have been more examined. Chromic 
acid is very soluble in water ; the taste of 
the solution is sharp and metallic ; it is of 
an orange-red colour ; by evaporation, ei- 
ther spontaneous or with a gentle heat, it 
affords crystals in long slender prisms, of a 
ruby-red colour. This acid combines with 
the alkalies, earths, and metallic oxides, 
forming neutral salts which are named 
chromates. , 
The combinations of this acid with me- 
tallic oxides are in general possessed of 
vei y beautiful colours, and are well adapted 
to form the finest paints. That with oxide 
of lead has an orange yellow, of various 
shade ; tliat with mercury, a vermillion 
red ; with silver, a carmine red ; with zinc 
and bismuth, the colours are yellow ; with 
copper, cobalt, and antimony, they are 
dull. 
CHRONOLOGY, is that science which 
relates to time, treats of the division of it 
into certain portions, as days, months, 
years, centuries, and the application of 
these portions, under various forms and 
combinations, as cycles, oeras, &c. to the 
elucidation of history. What is proposed 
in the present article is, to point out the 
chief methods by which the several por- 
tions of time have been computed, and 
in which they have been employed in as- 
certaining the connection, and determining 
the dates, of past transactions. 
The divisions of time which most pro- 
VOL. II. 
bably first attracted the notice of mankind, 
as most obvious to their senses. Were those 
marked by the revolutions of the heavenly 
bodies, days, lunar months, and years : and 
if these had corresponded so exactly to 
each other, that every lunation had con- 
sisted uniformly of the same number of 
days, and each year’ of a regular number 
of complete lunations, the business of 
chronology would have been attended with 
comparatively little difficulty. In conse- 
quence, however, of variations in the revo- 
lutions of the earth, which it is nOt requisite 
here to explain, it has become necessary^ 
to adjust these periods to each other by 
certain artificial divisions. Of these divi- 
sions : 
The Day claims our first notice, In com- 
mon speech, a day means that period of 
time which is included between the first 
appearance of light in the morning, and 
the return of darkness in the evening, or 
during which the sun is visible above the 
horizon. But the word is used, in a more, 
comprehensive sense, to denote tlie time of 
a complete revolution of the earth round 
its axis. The former has been denomi- 
nated a natural, the latter a civil, and some- 
times a solar, day. The beginning of the 
day has been variously reckoned by diffe- 
rent nations. The Chaldajans, Syrians, 
Persians, and Indians, reckoned the day 
to commence at sun-rise. Tire Jews, also, 
used this method for their civil, but began 
the sacred day at sun-set : this latter mode 
was used likewise by the Athenians, the 
Arabs, the ancient Gauls, and some other 
European nations. The Egyptians appear 
to have had several methods of reckoning 
their day; probably the mode varied in 
different parts of the country, and in the 
same place at different periods. The an- 
cient inhabitants of Italy computed the 
day from midiiight, and in this they have 
been followed by the English, French, 
Dutch, Germans, Spaniards, and Portu- 
guese ; modern astronomers, after the Ara- 
bians, count the day from noon. 
The day was subdivided by the Jew's 
and Romans into four parts, which they 
denominated watches or vigils : the first 
commenced at six in the morning, the se- 
cond at nine, the third at twelve, and the 
fourth at three in the afternoon. The be- 
ginning of the first watch was, by the Jews, 
called the tliird hour, and so on in succes- 
sion to the fourth watch, which was reckon- 
ed the twelfth hour. The night was di- 
vided in a sintilar manner. Other modes 
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