CRE 



CUE 



CREEPER, at sea, a sort of grapnel, 

 but without flooks, used for recovering 

 things that may be lost overboard. 



CRENATE, in Natural History, scol- 

 loped or notched at the margin. 



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 

 Syngenesia Polygamia JEqualis class and 

 order. Natural order of Composite 

 Semiflosculosx. Sichoracese, Jussieu. 

 Essential character: calyx calycled, with 

 deciduous scales, down hairy, stipitate ; 

 receptacle naked. There are twenty 

 species. 



CREPITATION, in chemistry, the 

 noise which some salts make over the fire 

 during calcination, called also DECRIPITA- 

 Tioif ; 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 crepusculum, or twilight, it is sup- 

 posed, usually begins and ends when the 

 sun is about 18 degrees below the hori- 

 zon ; for then the stars of the 6th magni- 

 tude disappear in the morning, and ap- 

 pear in the evening. It is of longer du- 

 ration in the solstices than in the equi- 

 noxes, and longer in an oblique sphere 

 than in a right one; because, in those 

 cases, the sun, by the obliquity of his 

 path, is longer in ascending through 18 

 degrees of latitude. 



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 lumi- 

 nous matter about the sun. This may 

 lengthen the duration 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 refraction of the at- 

 mosphere. 



The depth of the sun below the hori- 

 zon, at the beginning of the morning, or 

 end of the evening twilight, is determin- 

 ed in the same manner as the arch of vi- 

 sion; "viz. by observing the moment when 

 the air first begins to shine in the morn- 

 ing, or ceases to shine in the evening ; 

 then finding the sun's place for that mo- 

 ment, 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 degrees upon 



an average. Alhazen found it to be 19; 

 Tycho, 17; Rothman, 24; Stevenius, 

 18 ; Cassini, 15 ; Riccioli, in the equi- 

 nox 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 determina- 

 tions of astronomers is not to be wonder- 

 ed at, the cause of the crepusculum be- 

 ing inconstant ; for, if the exhalations in 

 the atmosphere be either more copious 

 or higher than ordinary, the morning 

 twilight will begin sooner, and the even- 

 ing hold longer, than ordinary; for the 

 more copious the exhalations are, the 

 more rays will they reflect, consequently 

 the. more will they shine ; and the higher 

 they are, the sooner will they be illumi- 

 nated by the sun. On this 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 bright- 

 ness of the atmosphere is variable, but 

 also its height from the earth : and there- 

 fore the twilight is longer in hot weather 

 than in cold, in summer than in winter, 

 and also in hot countries than in cold, 

 other circumstances being the same. But 

 the chief differences are owing to the 

 different situations of places upon the 

 earth, or to the difference of the sun's 

 place in the heavens. Thus, the twilight 

 is longest in a parallel sphere, and short- 

 est in a right sphere, and longer to places 

 in an oblique sphere, in proportion as 

 they are nearer to one of the poles ; a 

 circumstance which affords relief to the 

 inhabitants of the more northern coun- 

 tries, in their long winter nights. And 

 the twilights are longest in all places of 

 north latitude, when the sun is in the i ro- 

 pic of cancer ; and to those in south lati- 

 tudes, when he is in thetropic ofcapmcorn. 

 The time of the shortest twilighf is also 

 different in different latitudes : in Eng- 

 land, it is about the beginning of Octo- 

 ber 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 differ- 

 ence 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 

 ciescent in the Turkish symbol, witii its 

 points looking towards the top of the 

 chief, which is its most ordinary repre- 

 sentation, called crescent montant. Cres- 

 cents are said to be adossed, when their 





