COMMON THINGS THE ALMANACK. 



49. Ideler, in his " Handbuch der Mathematischen und Tech- 

 nischen Chronologic," in reference to this convention of Scaliger, 

 says that by its employment light and order were for the first time 

 let in upon the obscurity and confusion in which ancient history 

 and chronology were involved. 



Since the year of the birth of Christ was then the 4713th 

 of the Julian period, the order of any later year of the 

 Christian era in the Julian period will be found by adding 

 4713 to the year. Thus, for example, the year 1855 is the 

 1855 -f 4713 = 6568th year of the current Julian period. 



To find the order of any year before Christ in the Julian period, 

 it will be only necessary to subtract the year from the order of 

 the year 1 A.D. in the Julian period, that is, from 4714. Thus, 

 knowing that the date of the invention of the Metonic cycle wa& 

 432 B.C., its date in the current Julian period was 

 4714 432 = 4282. 



50. The Calendar, properly so called, is constructed differently 

 in different almanacks. In most, if not all, it gives for each 

 day the times at which the sun and moon rise and set, and the 

 time at which the latter passes the meridian ; the moon's age, 

 and the sun's declination. We shall briefly notice each of these 

 useful indications. 



51. The hours at which the heavenly bodies rise and set upon 

 the same day at different places are different. This arises either 

 from the different places being at different distances from the pole 

 oi the earth that is, having different latitudes, or being on 

 different meridians of the earth, that is, having different longi- 

 tudes. In either case the heavens, as seen from them, being 

 viewed from different stations, will be seen under different 

 aspects. Celestial objects, which will be invisible from one place, 

 will be visible from the other. The heavens may be considered 

 as a panorama, and the earth as a vast circular gallery or series 

 of galleries in its centre, to which a slow motion of revolution is 

 imparted, so as to exhibit to every spectator every part of the 

 great canvas of the heavens in succession. The parts of the 

 heavens seen by spectators, differently situated in these central 

 galleries, will obviously be different. An object which will be 

 just coming into the view of some, that is, rising, will be in full 

 front of others, that is, on their meridian, and will be disappear- 

 ing from others, that is setting. Spectators placed in the upper 

 galleries, that is, in northern latitudes, will look down upon 

 objects to which spectators in the lower galleries, that is, in 

 southern latitudes, will look up, and which spectators in the 

 middle galleries, that is, between the tropics, will see directly 

 before them. 



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