20 



GENERAL SCIENCE 



location of places and the reckoning of time. This line 

 is a circle which passes through the north point of the 

 horizon, the zenith the portion of the sky directly 

 over one's head the south point on the horizon, and 

 extends around the other side of the earth to the north 

 point again. 



It divides the sky into an east and a west half. When 

 the sun or moon crosses the meridian (mid-day line), 

 it has made half its daily journey from rising to setting. 

 The abbreviations A.M. and P.M. refer to the time when 

 the sun crosses the meridian, being taken from the Latin 

 phrases, ante meridiem and post meridiem. Since this 

 NORTH imaginary circle 



passes through the 

 zenith, there is a 

 celestial meridian 

 for every ob- 

 server. 



Meridians and 

 Parallels. - - For 

 purposes of cal- 

 culating distance 

 and time, imag- 

 inary lines are 

 drawn on the 

 earth's surface ex- 

 tending from pole to pole. These lines are at certain 

 intervals and lie on the earth directly under the celestial 

 meridian of the places through which they run. They 

 are numbered east and west, so many degrees from the 

 prime meridian, or the meridian of 0. This meridian 

 passes through Greenwich, England (Figure 17). 



Running at right angles to the meridians are the 



SOUTH 



FIG. 17. Parallels and Meridians. 



