766 GEOGRAPHICAL LATITUDE. 



provided the sky is comparatively free from clouds. Not only is the 

 position of each individual place of importance for the science of geog- 

 raphy, but the distance between places, as well as their direction one 

 from another, is also of great weight. So long as navigation was 

 confined to coasting, simple compass- directions and compass-maps 

 answered all necessary requirements ; but when mariners began to 

 strike out into the ocean, where they might wander for weeks without 

 seeing land, and it was found that the compass did not always point 

 directly north, but is liable to considerable variation, the old method 

 no longer sufficed ; a method of determining latitude at all times 

 became a pressing want, which, as is generally the case, resulted in 

 corresponding new inventions. The natural curiosity of civilized man 

 causes a longing to know the size of the planet on which he dwells. 

 This knowledge can be most readily gained by measuring accurately a 

 degree or rather various degrees of latitude. To accomplish this, gov- 

 ernments have provided immense sums of money, and scientists have 

 borne — not only without murmur, but with enthusiasm — the heat of 

 tropical summers and the cold of polar winters, the winds and fogs of 

 the mountains, and deluging rains in the plains, have suifered from 

 hunger and thirst, and even met bravely at their post, the one uncon- 

 querable. Death. It is to the contemplation of this gigantic work, 

 already continued for more than three centuries and still being vigor- 

 ously pursued, that we now turn. 



It may be well however to say first something as to the principles 

 which lie at the foundation of this work. 



Position of the tropics. — It was matter of very early observation that 

 the sun changes from time to time its position in the heavens in refer- 

 ence to the stars, and that this change is a regular one, and the period 

 of time occupied in returning to the same position determines the length 

 of the year. The path thus formed is called the Ecliptic' An imagi- 

 nary line on the surface of the earth formed by connecting those points 

 over which the center of the sun passes vertically at noon on each suc- 

 cessive day of the year, receives the same name. In connection with 

 this change of the sun's position, it was noticed that the length of the 

 shadows cast on the earth at noon at different seasons of the year is 

 variable,^ and this fact gave the first means of determining absolute 

 position on the globe. Noting in Egypt, where no shadow was cast, 

 only on one day of the year, gave the position of the northern tropic. 

 Half the difference between this point and that over which the sun 

 stood perpendicularly when farthest south, (accordingly when the 



iBriinnow, Astron., p. 75, defines the Ecliptic as" derKreis den derMittelpunkt der 

 Sonne, vom Mittelpunkt der Erde gesehen, im Laufe eines Jahres unter den Sternen 

 von Westen uach Osten besclareibt." 



2Tbat the sun's conrse is not parallel to the Equator is said to have been discovered 

 by Anaximander of Miletos (Strack's Plinius, lib. ii, 8. 6. Vol. i. p. 73). 



