MAGNETISM OF THE EARTH 



35 



Columbus. We know now that the reason for the declina- 

 tion of the needle is that the north end of it does not 

 point toward the north geographical pole as was at first 

 supposed but toward a point in the southwestern part of 



LINES OF EQUAL MAGNETIC DECLINATION IN THE UNITED STATES. 



Boothia Felix which is called the north magnetic pole. The 

 south magnetic pole as recently determined is a little to 

 the east of Victoria Land. 



These magnetic poles do not remain in the same place all 

 of the time but swing slowly back and forth, so that the 

 declination changes for the same place. On account of 

 this it is necessary for surveyors, who use the compass, to 

 find out the declination each year. The annual change in 

 the United States varies from to 5 seconds. In 1910 

 the decimation at Eastport, Maine, was 19.4 west and for 

 Seattle, Washington, 23.5 east. For intervening places 

 there were intervening values. Maps are now made with 



