90 THE WORLD. 



the star called Gamma, in the constellation Cepheus, will be the 

 pole star. The meridian VI, XVIII, is called the solstitial colure, 

 because it is the meridian which passes through the highest and 

 .lowest points of the ecliptic, which are called solstices, being the 

 meridian 18, P, 6, of the figure on page 91. 



We will now give some instances of the application of the pre- 

 cession of the equinoxes to chronology. Eudoxus, a celebrated 

 Greek astronomer, informs us, that in the celestial sphere, he had 

 observed a star which corresponded to the pole of the equator. 

 From various circumstances, we know Eudoxus lived about 

 the fourth century before Christ, hence it could not be our present 

 polar star which he observed, for at that time it was too far re- 

 moved from the pole. Upon reckoning back about 2000 years, 

 however, upon our man, we find a small star of the fifth magni- 

 tude, which may be the one observed by Eudoxus.- We are of 

 opinion that this star is the one meant by him. Others, however, 

 supposing Eudoxus to have borrowed his sphere from some older 

 source, have selected Kappa, in the constellation Draco, as the 

 star. This latter was the pole star about 1310 vears before Christ, 

 but in the time of Eudoxus, it was as far distant from the pole, 

 nearly, as was our present polar star. The little star we have been 

 considering, was the pole star about 200 years before the Christian 

 era, and as it is easily visible to the unassisted eye, was probably 

 the star meant by Eudoxr,?. 



The effect of the precession of the equinoxes, is to change the 

 right ascensions and declinations of the stars, for, as we have 

 more than once observed, right ascension is the distance from the 

 first point of Aries, but this point is continually changing its place 

 in the heavens. It also changes what is called the longitude of 

 the stars. The longitude of a star, is, like right ascension, 

 reckoned from the first point of Aries eastward, but upon the 

 ecliptic instead of the equator, thus, of R. A. and of Long, 

 are both reckoned from the same point. See the next figure, 

 where the right ascension is marked 0, 1, 2, 3, 4, &c., and 

 longitude is marked 0, 1, II, III, IV, &c. Declination is distance 

 north or south of ftie equator, but latitude is distance north or 

 south of the ecliptic, hence, when a star happens to be in the 



