454 



GENEKAL SCIENCE 



LOCATION 



Direction. Since the earth turns upon its axis, man has estab- 

 lished certain points which are called points of the compass. The 

 earth turns toward the dawn point which is called the east. The 

 opposite of that direction is called the west. 



The North Star remains fairly 

 constant over the North Pole of 

 the earth, and is used to deter- 

 mine direction. The common 

 method of determining direction, 

 however, is through the aid of 

 the compass, which consists of a 

 bar of magnetized steel, or needles, 

 so suspended that the bar or card 

 to which the needles are attached 

 will swing freely in a horizontal 

 plane. The bowl of the compass 

 is constructed of copper or brass, 

 and the dial is fitted with an 

 agate cup in the center, placed 

 upon a sharp point to allow the 

 needle or dial to swing freely. 

 On shipboard the dial floats in 



FIG. 343.-Notice the pointers and alcoho1 to kee P the card level 

 the earth's axis, each in line with as the ship rolls and pitches, 

 the pole star. The compass does not point to 



the North Pole of the earth but 



to a North Magnetic pole on Boothia Island in Northern Canada. 

 Find the island on the map. 



There are a few places in the United States where the compass 

 will point to the earth's true north. The amount of variation 

 between the north pole and the north magnetic pole is called decli- 

 nation; and navigating officers must allow for this in working out 

 the true north when sailing. They are provided with government 

 charts which show the exact amount of declination. 



Longitude. The longitude of any place on the earth is measured 



