4 LATITUDE AND LONGITUDE. 



In this way the English geographers begin to 

 count from the meridian of Greenwich near London ; 

 the French from the meridian of Paris. By the term 

 meridian generally, therefore, we understand a great 

 circle of the sphere NS perpendicular to the horizon, 

 and which passes through the poles of the world ; 

 we term it the meridian, because it cuts all the pa- 

 rallels of latitude FG, HI, &c. into two equal parts; 

 and also divides into two equal parts the duration of 

 a celestial body above the horizon. Directly the sun 

 appears over this circle, it is said to be on the meri- 

 dian, and we call it mid-day or 12 o 'clock ; and by 

 the portion of time which elapses before its return 

 again to this same meridian, we measure the dura- 

 tion of the day, which has been divided into 24 

 hours ; now, Astronomers count those 24 hours in 

 succession from one mid-day to another, but in com- 

 mon life they are divided into two portions of 12 

 hours each ; the first extends from mid-day until 

 twelve hours after, or midnight ; the second from 

 midnight again unto mid-day; the first 12 have 

 been termed hours of evening, the second hours of 

 morning. 



We may perceive therefore, that every place situ- 

 ated on the same meridian will have mid-day at the 

 same absolute moment of time : and the same may 

 be said for any other hour whatever. If through 

 the earth's axis we imagine any number of planes, 

 all the different sections which they would form on 

 the surface might be considered as so many meri- 

 dians, to which the sun would correspond success- 

 ively during the day; by which we perceive that 

 when it is mid-day to those situated on some given 

 meridian, it would be more than mid-day to those 

 situated on meridians toward the east, and not yet 

 mid-day to those situated on meridians toward the 

 west ; for the sun would have passed over the mer- 

 idians toward the east, and not yet have arrived at 

 those toward the west, and this is true for any hour 

 whatever, and arises from the earth's motion on its 



