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CHRONOLOGY. 



C-HlOlrOLOOV, from xfH limf, and A*y*t doctrine, is 

 that science which treats of the natural and artificial di- 

 Titioni of time, and refer* to the points which it tlmi 

 mark* out, the various events recorded in history, &c. 



I" order to convey to our readers as full and distinct 

 an account of this useful subject a* our limits will per- 

 mit, we shall divide it into the following Chapters : 

 I. MATHEMATICAL CHRONOLOGY; II. HISTORICAL 

 CHRONOLOGY ; III. COMPARATIVE CHRONOLOGY ; and, 

 IV. TABULAR CHRONOLOGY. 



CHAP. I. 



Mathematical Chronology. 



MMhetai. MATHEMATICAL chronology treats of the division of 

 tir.il chrr. l ' mc by dav, months, years, and cycles, and of the ap- 

 nolofT. plication of these divisions to the purposes of civil life. 



SECT. I. On the Day. 



11 l! -e A day is that portion of time which elapses while the 



earth performs a complete revolution about its axis ; and 

 its length is measured by observing the precise instant 

 when the centre of a star passes the meridian on two 

 consecutive days. A day thus measured is called the si- 

 dereal day, and consists of 23 hours, 56' 3".4. A solar 

 or natural day, is that portion of time which elapses be- 

 tween the arrival of the sun at the meridian on two con. 

 tecutive days. The mean length of the solar day is 24 

 hours ; but, owing to the inclination of the earth's axis 

 to the ecliptic, and the unequal motion of the earth in 

 its orbit, the solar days are of unequal length, some- 

 times exceeding, and sometimes falling short of 24 hours. 

 The hour hand of a well-regulated clock performs two 

 complete revolutions on the dial plate in the course of a 

 mean solar day, and twice 36.5 or 720 revolutions in the 

 course of a year ; whereas the shadow of the stile or 

 gnomon of a sun dial, sometimes performs more and 

 sometimes less than one revolution during a mean solar 

 day, but always completes 365 revolutions in the course 

 of one year. The difference between the mean solar time, 

 as shewn by a well-regulated clock, and the apparent 

 time, as shewn by a sun dial, is called the equation of 

 time, or the equation of natural days, and has been fully 

 explained in the article ASTRONOMY, Vol. II. Pp. 652, 

 797. 



Although the inhabitants of every country have agreed 

 in adopting the mean solar day as the unit of their scale 

 for measuring time, yl they have differed from each other 

 in fixing its commencement. The following Table will 

 shew distinctly the practice of various ancient and mo- 

 dern nation*. 



Athenians and the inhabitants of Attica 



The Marcomanni 



Austrians 



Turks 



Bohemians 



T.ble of 



Table thriving the Time* at which different Nations have 

 begun or begin the Civil Day. 



Ancient Babylonian* at sunrise. 



.it Persians ditto. 



Ancient Syrians ditto. 



Ancient Jews ditto. 



Almost all Eastern nations ditto. 



Inhabitants of Majorca, Minorca, and Ivica . ditto. 

 'J !. Greeks and the inhabitant* of the islands 

 ot the Archipelago ditto. 



at sunset. 



ditto. 



ditto. 



ditto. 



ditto. 



Silesians ditto. 



Italians diuo. 



Ancient Umbrians at mid-day. 



Ancient and modem Arabians ditto. 



Astronomers of all nations ditto. 



Ancient Egyptians midnight. 



English ditto. 



French ditto. 



Germans ditto. 



Dutch ditto. 



Russians ditto. 



Spaniards ditto. 



Swiss ditto. 



Portuguese ditto. 



Danes ditto. 



Swedes, Laplanders, Americans, and Arau- 



caniani ditto. 



Modern Chinese ditto. 



The subdivision of the day into particular part* has Sulxlm- 

 likewise been different among different nations. The si<m of 

 Chaldeans, Syrians, Persians, Indians, Jews and Ro- the day. 

 mans, divided both the day and night into four parts. 

 The Greeks divided the natural day into 12 hours in 

 imitation of the Babylonians, and this practice was after- 

 wards adopted by the Romans. Among almost all modern 

 nations, the day is divided into 24 hours, reckoned twice 

 from 1 to 12, except among the Italians, Bohemians, 

 and Poles, who reckon them from 1 to 24. The Arau- 

 camans divide the natural day into 12 parts, oach of which 

 has a particular name. The Turks follow the practice 

 of the Jews; and the Chiuese divide the mean solar day 

 into 12 hours, each of which is of course equal to two 

 of ours. In the decimal system adopted by the French, 

 the day is divided into 10 hours. 



The various methods which hare been employed for 

 measuring the subdivisions of the mean solar day by Clep- 

 sydra, Dials, Cluckt, and Watches, will be discussed 

 under the articles DIALLING, HOUOLOGY, HYDRODY- 

 NAMICS, and TIMEKEEPER. 



SECT. II. On the Month. 



The next convenient division of time which is mark- On the 

 ed out by the revolutions of the heavenly bodies is the month, 

 month. The astronomical month is the time in which 

 the moon performs a complete revolution round the hea- 

 vens, and is either periodical or si/nodical. The vet itiili- 

 cal month is the time in which the moou moves from one 

 point of the heavens to the same point again, and i equal 

 to 27 d 7 h 43' 4".7 ; and the synodical month, or lunation 

 as it is sometimes called, is that portion of time which 

 elapses between two successive new moons, or between two 

 luccessive conjunctions of the moon with the sun, and is 

 equal to S^IS 11 44' 3" 11'". The solar month is that por- 

 tion of time in which the sun moves through one sign of the 

 ecliptic, and is equal at an average to SO" 10" 29' 5". The 

 civil month, which is formed for the purposes of civil life, 

 is one, which consists of a certain number of whole days, 



