OF THE HEAVENS AND THE EARTH. -*283 



that the north pole of the heaven is directly over the 

 north pole of the earth; and the south pole of the 

 heaven is directly over the south pole of the earth. 



The equator is a great circle upon the earth, every 

 part of which is equally distant from either of the two 

 poles. It divides the earth into two equal parts, called 

 the northern and southern hemispheres. If we suppose 

 the plane of this circle to be extended to the heaven, it 

 will mark the equinoctial therein, and will divide the 

 heaven into two equal parts, called the northern and 

 southern hemispheres of the heaven. 



The meridian of any place is a great circle passing Meridian. 

 through that place and the poles of the earth. We 

 may imagine as many such meridians as we please, be- 

 cause any place that is ever so little to the east or west 

 of any other place, has a different meridian from that 

 place ; for no one circle can pass through any two such 

 places and the poles of the earth. 



The meridian of any place is divided by the poles into 

 two semicircles : that which passes through the place is 

 called the geographical, or upper meridian ; and that which 

 passes through the opposite place, the lower meridian. 



When the rotation of the earth brings the plane of jvoon and 

 the geographical meridian to the sun, it is noon or mid- mid nig *' 

 day, to that place ; and when our lower meridian comes 

 to the sun, it is midnight- 

 All places lying under the same geographical meri- 

 dian, have their noon at the same time, and consequently 

 all the other hours. All those places are said to have 

 the same longitude, because no one of them lies either 

 eastward or westward from any of the rest. 



If we imagine 24 semicircles, one of which is the geo- H<nn cir- 

 graphical meridian of a given place, to meet at the poles 

 and to divide the equator into 24 equal parts : each of 

 these meridians will come round to the sun in 24 hours 

 by the earth's equable motion round its axis in that 

 time. And, as the equator contains 360 degrees, there 



