CHAMBERS'S INFORMATION FOR THE PEOPLE. 



YEARS OF PRINCIPAL ERAS CORRESPONDENT TO 1872. 



Years. Abbrev. 



Era of Creation (Constantinopoli- 



tan account) 7381 A.M. Const. 



Era of Creation (Alexandrian 



account) 73$4 A - M - Alex - 



Era of Creation (Jewish account), 



23d Thebet 5 6 3 2 A.M. 



Julian Period 6585 Jul. Per. 



Caliyug (Hindu). .Poos or Margaly, 4973 Cal. 



Olympiads... 7th month 1st year of 663 Olymp. 



Era of Rome 2625 A.U.C. 



Era of Nabonassar.. .8th month of 2620 JEx. Nab. 

 Era of Death of Alexander 



3d month, 2197 A. Mort. Alex. 

 Diocletian, or era of Martyrs 



25th Cohiac, 1588 Mr. Diocl. 



Hegira 22d Rabiu II. 1295 A.H. 



MISCELLANEOUS PERIODS. 



Besides these major periods, we have others of 

 less significance, but still useful to be known, as 

 they are frequently alluded to in works of a histori- 

 cal nature. Thus, a lustre (Lat. lustrum) is a 

 period of five years ; or, more properly, the com- 

 pletion of fifty months, at the end of which term 

 a census was taken of the Roman population. A 

 generation is the interval of time elapsed between 

 the birth of a father and the birth of his son, and 

 is generally used in computing considerable periods 

 of time both in sacred and profane history. The 

 interval of a generation is consequently of uncer- 

 tain length, and depends on the standard of 

 human life, and whether the generations are 

 reckoned by eldest, middle, or youngest sons. 

 Thirty years are usually allowed as the mean 

 length of a generation, or three generations for 

 every hundred years. A reign is the interval that 

 elapses between the accession and demise of a 

 monarch or supreme governor, and is a term in 

 frequent use by historians. It is a period, how- 

 ever, of very uncertain duration, and differs in 

 different countries, according as the sovereign may 

 be liable to assassination, deposition, and the like. 

 Dr Hales has, however, shewn that the average 

 standard of reigns is about twenty-three years, 

 reckoning from a series of 454 kings in 10,105 

 years. A century (centum, a hundred) is a period 

 of one hundred years, reckoning from the com- 

 mencement of the first year in any given century ; 

 thus the current century is the nineteenth of the 

 Christian era. 



TABULAR CHRONOLOGY. 



Under this head the leading events, phenomena, 

 or facts recorded in history, are arranged in the 

 order of time in which they have occurred that 

 is, in chronological order. Referring the reader 

 to the systematic chronologies of Newton, Blair, 

 Playfair, Sir Harris Nicolas, and others, we shall 

 merely remark, that the best mode of tabulating 

 events is that which exhibits the dates in bold 

 characters, and endeavours to arrange in juxta- 

 position the leading occurrences in the principal 

 countries of the world. By these means, reference 

 is greatly facilitated, and a notion of civil progress 

 more intelligibly conveyed. The language of 

 tabular chronology should always be concise, 

 elliptical rather than expletive a mere indication 

 rather than an account of the event recorded. 



m 



HOROLOGY. 



Reference has already been made to the heavenly 

 bodies and their motions as the most primitive and 

 natural, as well as most perfect time-keepers. Our 

 attention here, therefore, must be confined to those 

 artificial machines which have been invented 

 chiefly for the purpose of adding to the conveni- 

 ence of these, by dividing the unit of astronomical 

 time-keeping namely, the day into fractional 

 parts, such as hours, minutes, and seconds ; there 

 being no such convenient and desirable measure- 

 ment obvious in nature. The science which 

 explains the methods of so measuring and mark- 

 ing the fractional parts of the day is termed 

 horology, from two Greek words, signifying hour 

 and discourse a term comprehensive of every 

 time-keeping contrivance, from the simplest sand- 

 glass to the most perfect chronometer. The in- 

 struments to which we shall here advert are dials, 

 depending upon the shifting shadow of an object 

 illuminated by the sun ; clepsydrae, depending 

 upon the equable flow of a liquid ; and clocks 

 and watches,* whose movements are determined 

 by weights and springs. 



SUN-DIALS. 



Long before the invention of any artificial time- 

 keeper, the interval between sunrise and sunset 

 was really divided, with no little accuracy, even 

 amongst the rudest nations, simply by the shorten- 

 ing, turning, and lengthening of the shadows of 

 trees, rocks, and mountains ; and it was this primi- 

 tive mode of dividing the day which no doubt 

 naturally suggested the first idea of sun-dials. 

 The earliest time-measurer of this description of 

 which we have any historical notice, is the dial of 

 King Ahaz, who lived about 742 years before the 

 birth of Christ. According to Herodotus, the 

 Greeks learned the use of them from the Chal- 

 deans, probably through the Babylonian priest 

 and astronomer Berosus. Mention is made of the 

 hemisphere or dial of this philosopher ; and the 

 octagonal Temple of the Winds, which is still 

 standing, shews on each side the lines of a vertical 

 dial, and the centres where the gnomons were 

 placed. In Rome, sun-dials were not known till 

 293 B.C., when one was erected near the Temple 

 of Quirinus the rising and setting of the great 

 luminary being the only standards of reckoning 

 previous to this period. The Romans at this 

 time were not aware that a dial made for Rome is 

 not suited to other places. The ancients used 

 hemispherical dial-plates, constructed to shew 

 equal divisions of the time between sunrise and 

 sunset, or temporary hours, which varied in length 

 with the seasons. The correct theory and practice 

 of dialling belong to modern times. Vertical plain 

 dials were at one time prevalent, as may be seen 



* Although modern machines for measuring time are designated 

 by the general appellation of clocks and watches, they are also- 

 distinguished by peculiar names arising from certain modification* 

 in their construction, or from certain particular purposes they are- 

 intended to serve. By the term clock is understood an instrument 

 which not only shews, but also strikes the hours ; a time-piece is- 

 one which shews the hours without striking them ; a quarter- 

 clock is one which strikes the quarters as well as the hours ; an 

 astronomical clock is one which shews sidereal time ; a watch is- 

 a portable or pocket time-piece ; a repeater is one having a con- 

 trivance, by means of which it can be made to repeat the hours ;. 

 a chronometer is a watch of the best kind, or one fit to be employed 1 

 for astronomical purposes. Brandt's Dictionary of Science. 



