CRE 
giire of inevitable circumstances, but it is 
not the less alarming on that account. 
CREEPER, at sea, a sort of grapnel, 
but without Hooks, used for recovering 
things that may be lost over-board. 
CRENGLES, among seamen, small 
ropes spliced into the bolt-ropes of the sails 
of the main-mast and fore-mast, into which 
the bowling bridles are made fast. 
CREPIS, in botany, a genus of the Syn- 
genesia Polygamia ./Equalis class and order. 
Natural order of Composite, Semifloscu- 
los®. Cichoraceae, Jussieu. Essential cha- 
racter : calyx calycled, with deciduous 
scales, down hciiry, stipitate ; receptacle 
naked. There are twenty species. 
CREPITATION, in chemistry, the noise 
which some salts make over the fire during 
calcination, called also Decripitation, 
which see. 
CREPUSCULUM, twilight, the time 
from the first dawn or appearance of the 
morning, to the rising of the sun ; and again, 
between the setting of the sun, and the last 
remains of day. 
The crepuscjdum, or twilight, it is sup- 
posed, nsnally begins and ends when the 
sun is about 18 degrees below the horizon ; 
for then the stars of the 6th magnitude 
disappear in the morning, and appear in the 
evening. It is of longer duration in the 
solstices than in the equinoxes, and longer 
in an oblique sphere than in a right one ; 
})ecause, in those cases, the sun, by the obli- 
quity of his path, is longer in ascending 
through 18 degrees of altitude. 
Twilight is occasioned by the sun’s rays 
refracted in our atmosphere, and reflected 
from the particles of it to the eye. Kepler 
indeed assigned a different cause of the 
crepusculum, viz. the luminous matter 
about the sun. This may lengtlien the du- 
ration of the twilight, by illuminating the 
air, when the sun is too low to reach it with 
his own light, but is not the principal cause 
of it : which is unquestionably the refrac- 
tion of the atmosphere. 
The depth of the sun below the horizon, 
at the beginning of the morning, or end of 
the evening twilight, is determined in the 
same manner as tlie arch of vision ; viz. by 
observhig the moment when the air first be- 
gins to shine in the moming, or ceases to 
shine in the evening ; then finding the sun’s 
place for that moment, and thence the 
time till his rising in the horizon, or from 
his setting in it in the evening. It is now 
generally agreed that this depth is about 18 
Agrees upon an average. Albazen found 
CRB 
it to be 19" ; Tycho, 17”; Rothman, 24” ; 
Stevenius, 18”; Cassini, 15”; Riccioli, in 
the equinox in the morning 16°, in the 
evening 20” 30' ; in the summer solstice in 
the morning 21” 25.', in the winter solstice 
in the morning 17° 25'. 
This difference among the detennina- 
tions of astronomers is not be wondered at; 
the cause of the crepusculum being incon- 
stant ; for, if the exhalations in the atmos- 
phere be either more copious or higher 
than ordinary, tlie morning twilight will be- 
gin sooner, and the evening hold longer 
than ordinary ; for the more copious the 
exhalations are, the more rays will they re- 
flect, consequently the more will they shine ; 
and the higher they are, the sooner will 
they be illuminated by the sun. On tiiis 
account too, the evening twilight is longer 
than the morning, at the same time of the 
year, in the same place. To this it may be 
added, that in a denser air the refraction is 
greater ; and that not only the brightness of 
the atmosphere is variable, but also its 
height from the earth : and therefore the, 
twilight is longer in hot weatlier than in 
cold, in summer than in winter, and also in 
hot countries than in cold, other circum- 
stances being the same. But the chief dif- 
ferences are owing to the different situations 
of places upon the earth, or to the difference 
of the son’s place in the heavens. Thus, the 
twilight is longest in a parallel sphere, and 
shortest in a right sphere, and longer to 
places in an oblique sphere in propoi tion as 
they are nearer to one of the poles ; a cir- 
cumstance which affords relief to the inha- 
bitants of tlie more northern countries, in 
their long winter nights. And the twi- 
lights are longest in all places of north lati- 
tude, when the sun is in the tropic of can- 
cer; and to those in south latitude, when he 
is in the tropic of capricorn. The time of 
the shortest twilight is also different in dif- 
ferent latitudes : in England, it is about the 
beginning of October and of March, when 
the sun is in the signs Libra and Pisces. 
CRESCENT, in heraldry, a bearing in 
form of a new moon. It is used either as 
an honourable bearing, or as the difference 
to distinguish between elder and younger 
families ; this being generally assigned to 
the second son, and those that descend 
from him. The figure of the crescent is the 
Tnrkisli symbol, with its points looking to- 
wards the top of the chief, which is its 
most ordinary representation, called cres- 
cent montant. Crescents are said to l>e 
adossed, when their backs are turned to^ 
