LATITUDES AND LONGITUDES. 



pole star is very near the pole, it is not exactly at it ; there is, 

 in fact, no star exactly at the pole, and there being no visible 

 object there, it is impossible to measure directly its distance 

 from the zenith. This difficulty is eluded by measuring the 

 distance of the zenith from some star, or other celestial object, 

 whose distance from the pole happens to be known : for example, 

 suppose that there were a star directly between the zenith and 

 pole, whose distance from the pole was known to be 10. Then 

 if we find the distance of the zenith from this star to be 40, 

 we should immediately infer the distance of the zenith from the 

 pole to be 50. 



It is in fact, then, by this device that the latitude is always 

 ascertained. By various observations made by astronomers, the 

 positions of most of the stars and other celestial objects, with 

 respect to the poles, are known and recorded ; and when we 

 desire to determine the latitude of any place, we measure the 

 distance of the zenith of that place from some celestial object 

 whose position with respect to the pole is known, and thence 

 infer the position of the place with respect to the terrestrial pole ; 

 and from that deduce at once the latitude. 



7. But our purpose would be equally served if we were supplied 

 with the position of any visible object with reference to the 

 celestial equator. Thus, if we know the distance of the centre ot 

 the sun from the celestial equator, we shall readily be able to 

 find the latitude ; for it would only be necessary when the sun is in 

 or very near the meridian, that is, at or near noon, to measure 

 the distance of the zenith of the place from the centre of the 

 sun. This would be done by measuring the distance of the 

 zenith, first from the upper, and then from the lower limb of the 

 sun. The distance from the centre would be the mean between 

 these. 



Let us suppose, for example, that the sun being between the 

 zenith and the equator, we find that the distance from the zenith 

 to the centre of the sun is 20, and that we also ascertain from* 

 the table of the position of the sun, that the distance of the centre 

 of the sun at that time from the equator, is also 20, we should 

 infer at once that the distance of the zenith from the equator 

 must be 40, and that such, therefore, must be the latitude of the 

 place. 



This method of ascertaining the latitude is, perhaps, the most 

 easily practicable. The observations may be performed daily, at 

 noon, when the sun is visible : and in all almanacs, the distance 

 of the centre of the sun from the equator, which is called the 

 sun's declination, is registered. The instrument by which the 

 observations are executed on land is, usually, a quadrant fur- 

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