CHRONOLOGY; 39 



confifts in fixing the dates of all thofe events that 

 are related in hiftory, and of ranging them in the 

 feveral divifions of time in which they occurred: 

 and by this means chronology becomes one of 

 the eflential parts of hiftory. This fecond part 

 of chronology draws its principles from the firft i 

 but it has need of other lupports, as of criti- 

 cifm, of the teftimony of authors, of ancient 

 coins, medals, infcriptions, &c. of fuch epochs 

 in hiftory as are inconteftable , of eclipfes of the 

 iun and moon, and other aftronomical obferva- 

 tions, &c. We (hall now make the analyfis of 

 chronology according to this natural divilion, 

 and fhall confider it from thefe different points 

 of view. 



IV. The time that the fun employs in going 

 completely round the earth is called a day. 

 alfo call that time the fun remains above 

 the horizon, day ; and the time he is under ir, 

 night. As the fun's motion is flower when he is 

 in the apogee than when in the perigee, it fol- 

 lows that the firft fort of days, which are allb 

 called natural days, muft be fhorter in fummer 

 than in winter. The natural day is divided into 

 iour-and-twenty hours, the hour into fixty mi- 

 nutes, and the minute into fixty feconds. As 

 the point of mid-day or noon can be oblcrved, 

 by means of the meridian, with thr greateft pre- 

 cilion, aftronomers begin the day at that point, 

 count twenty-four hour* in ku t cilion -, 

 which, when thus counted, are callrd ailronomic 

 hours. The common people, on the com: 



begin 



