AIM GEOGRAPHY AND ASTRONOMY. other is never seen, so there are some stars which never set, and others which never rise in their horizon. Their days and nights are of very different lengths according to the different declination of the sun in the several seasons of the year. In this oblique position of the sphere, astronomers some- times talk of the oblique ascension of the sun or stars ; and in order to obtain a clearer idea of it, let us again consider the right ascension, which is the sun or star's distance from that meridian, which passes through the point aries, measured on the equator. Or it may be expressed thus : The right ascension is that degree of the equator which comes to the meridian together with the sun or star, considered in its distance from the point aries. But the oblique ascension is that degree of the equator which in an oblique sphere rises together with the sun or star considered in its distance from the point cries. Note, That in a right or direct sphere all the heavenly bo- dies can only have right ascension, and no oblique ascension ; because the same point or degreeof the equator that rises with them crimes also to the meridian with them : But in an oblique sphere there is sometimes a great deal of difference between the point that rises with them and the point that comes with them to the meridian. Now the difference between the right ascensionof the sun or star, and its oblique ascension is called the ascensional difference. Note, Concerning the-stars in the equator, that their right and oblique ascension are et.,jal : Therefore the sun in the equi- noxes rising at six and setting at six has no ascensional differ- ences: But as he goes onward from the equator toward the winter solstice, he rises after six ; and as he goes toward the summer he rises before six; and the distance of his rising or setting from six o'clock is called the ascensional difference. And perhaps it is sufficient as well as much easier for a learner to remember that the time of the sun or star's rising or setting before or after six o'clock is called by astronomers the ascensional difference, without taking any notice at all of the oblique ascension, which is neither so easy to be apprehended or remembered. The second distinction of the inhabitants of the earth may bemade according to thefive zones, which they inhabit ; this was an ancient division of the globe. The zones are broad circles, five of which cover or fill up theglobe. There are two temperate, twofrigid or cold, and one torrid or hot. The torrid or burning zone is all the space that lies be- tween the two tropics; it was once counted uninhabitable, because of excessive heat,, being so near the sun; but later discoveries bave found Many and great nations inhabiting
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