The Earth considered as a Planet. 77 



that the sun has only the lower half of his 

 disk hid from the inhabitants on that cir- 

 cle for a few minutes about midnight. 



After this the days begin to shorten in 

 the northern parts of the world, and the 

 nights lengthen in proportion as the earth 

 advances to the first point of Aries, at 

 which it arrives on the 23d of September, 

 when the sun, as seen from the earth, 

 will appear in .Libra. On this day the 

 sun will be in the equinoctial again, and 

 the days and nights will again be equal 

 all over the globe. As the earth pro- 

 ceeds on its orbit from this point, the 

 north pole gradually goes into the dark ; 

 and the south pole advances into the err- 

 lightened hemisphere ; and on the 22d of 

 December, when the earth enters Cancer, 

 and the sun appears at Capricorn, the 

 north pole will be as far as it can be in the 

 dark, which is 23-| degrees, equal to 

 the inclination of the earth's axis from a 

 perpendicular to its orbit : and then, the 

 northern parts are as much in the dark as 

 they were in the light on the 21st oijime; 

 the winter nights being as long as the 

 summer days, and the winter days as 

 short as the summer nights. 

 G 



