CHRONOLOGY-HOROLOGY. 



HP HE general relation of events and successive 

 _L existences to each other we denominate Time 

 a thing of duration, involving the past, the pres- 

 ent, and the future. It is evident that for the 

 measurement of time we can have no standard of 

 the same tangible nature with a pound, a yard, or 

 a pint measure. We must have recourse to the 

 space or duration involved in some continued or 

 reiterated motion, as to which we have all the 

 proof possible in the nature of the thing, that it 

 requires the same period for its recurrence on one 

 occasion as on every other. The motions of the 

 heavenly bodies are of such a nature, and present 

 the surest standard of reckoning time on a large 

 and comprehensive scale. For periods, however, 

 less in duration than a single day, or day and 

 night, there are no explicit natural standards ; 

 hence the utility and necessity of mechanism of 

 human invention, the motions of which, mathe- 

 matically adjusted and numbered, shall measure 

 and record more brief and arbitrary divisions. 



In accordance, therefore, with what is the com- 

 mon practice of mankind in applying such a scale 

 of time to the general routine and business of life, 

 especially in its more civilised condition, we pur- 

 pose to treat first, of the measurement of time 

 by days, months, years, and cycles, considered 

 with special reference to their respective natural 

 and artificial subdivisions and accumulations ; 

 and, secondly, of those instruments and machines 

 which have been invented for dividing the leading 

 astronomical unit, or day, into seconds, minutes, 

 and hours. The former of these departments may 

 be termed Chronology, or the science of time in 

 general ; the latter, Horology, or an explanation of 

 the various contrivances which have been devised 

 for marking and measuring its arbitrary subdi- 

 visions. 



CHRONOLOGY. 



Chronology from chronos, time, and logos, dis- 

 course is literally the doctrine of time ; the 

 science which treats of its various divisions, and 

 of the order and succession of events. The chro- 

 nologist has thus a threefold duty to perform 

 namely, to assign a measure to the interval which 

 elapses between successive recurrences of any 

 natural event ; to determine certain points or 

 epochs from which to date occurrences, whether 

 preceding or succeeding that epoch ; and, lastly, 

 dating from any given epoch, to arrange in due 

 order all facts and phenomena which may be con- 

 sidered of importance. Adopting this course, we 

 shall treat, in the first place, of the division of 

 time into 



DAYS AND HOURS. 



A day, in the ordinary sense, is one complete 

 alternation of light and darkness, caused by the 

 revolution of the earth on its axis. It takes rather 

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more than a complete revolution of the earth to 

 bring a spot on its surface back into the same 

 position with regard to the sun, because the sun 

 has in the meantime moved forward a little in the 

 sky. The period that thus elapses is a natural or 

 solar day. These periods, however, are not of ex- 

 actly the same length at all seasons of the year, and 

 therefore the mean length is taken as the standard, 

 and is called the m/z/day. It is this civil day, 

 divided into twenty-four equal parts called hours, 

 that our clocks and watches keep. The period 

 of a complete revolution of the earth, which is 

 determined by two successive culminations of a 

 fixed star, is called a sidereal day, and is shorter 

 than the mean day by nearly four seconds (see 

 ASTRONOMY). We have thus three species of 

 day the sidereal, or that time which elapses 

 between two successive culminations of the same 

 star, and which is now universally adopted by 

 astronomers in their observatories ; the solar, 

 natural, or apparent day, being the time that 

 elapses between two consecutive returns of the 

 same terrestrial meridian to the centre of the sun, 

 and which consequently commences at noon ; and 

 the civil or mean solar day, which is the mean or 

 average of these meridional returns, and which 

 most modern nations have adopted, placing the 

 commencement and termination at mean mid- 

 night. 



The succession of day and night would un- 

 doubtedly constitute the first great natural period 

 reckoned by the human race involving, as it 

 does, not only the most familiar and most strik- 

 ingly contrasted phenomena within the bounds 

 of man's experience, but phenomena peculiarly 

 adapted to the great necessities of his nature 

 those of vigilance and sleep. Yet the precise point 

 at which the day should be held to begin and ter- 

 minate, must have been a matter much less easily 

 settled ; and accordingly we find, that while 

 amongst ancient nations the Babylonians, Per- 

 sians, Syrians, Greeks, and almost all the nations 

 of Asia the day began at sunrise, and was held 

 to last throughout the whole of the ensuing 

 daylight and darkness an arrangement better 

 adapted to countries near the tropics than else- 

 where, as the sun there rises more nearly about 

 the same time throughout the year the Jews, 

 Turks, Austrians, and others, with some of the 

 Italians and Germans, have begun their day about 

 sunset ; the Arabians theirs at noon, as do astron- 

 omers and navigators of all nations ; the ancient 

 Egyptians, and most of the modern Europeans 

 and Americans, on the other hand, as well as the 

 modern Chinese, beginning theirs at midnight, 

 which is evidently the most convenient method, 

 since it throws all the waking and active portion 

 of the day under one date. 



In the civilised part of the world, it is now 

 customary to divide the day, and reckon the 

 minuter portions of time, by instruments, to be 

 afterwards described, in seconds, sixty of which 

 constitute a minute ; in minutes, sixty of which 



