THE CONQUEST OF THE ZONES 



vary in the direction of its horizontal action, but it also 

 tends when suspended at the middle to shift its vertical 

 axis. In regions near the equator, indeed, the mag- 

 netized needle maintains a horizontal position, but if 

 carried into northern or southern latitudes it pro- 

 gressively "dips," its polar end sinking lower and lower. 

 This dipping of the needle seems to have been first 

 observed by Robert Norman, an English nautical in- 

 strument maker, about the year 1590. It was brought 

 to the attention of Gilbert and carefully tested by him 

 in the course of his famous pioneer experiments. Gil- 

 bert was led to predicate the existence of magnetic 

 poles, the exact location of which would be indicated 

 by the dipping needle, which, sinking lower and lower 

 as northern latitudes were attained, would ultimately 

 at the magnetic pole itself assume a vertical direction. 



That this is a correct expression of the facts was 

 determined in the year 1 831 by Sir James Ross, who in 

 the course of his Arctic explorations observed the verti- 

 cal dip and so located the northern magnetic pole at about 

 70 degrees 5 minutes north latitude and 96 degrees 43 

 minutes west longitude. It was thus proved that the 

 magnetic pole is situated a long distance — more than 

 1,200 miles — from the geographical pole. The location 

 of the south magnetic pole was most accurately deter- 

 mined in 1909 by Lieutenant Shackleton's expedition 

 at about 73 degrees south latitude and 156 degrees east 

 longitude. The two magnetic poles are thus not directly 

 opposite each other on the earth's surface, and the 

 magnetic axis of the earth does not coincide with the 

 geographical center of the globe itself. 



[13] 



