8 THE LAST CRUISE OF THE CARNEGIE 



made a landfall somewhere on the northwest coast of 

 Scotland. In brief, while the sailing directions as gov- 

 erned by the winds and currents on the Atlantic Ocean 

 are the same now as they were in Halley's time, the 

 magnetic directions or bearings of the compass that a 

 vessel must follow across the Atlantic to reach a given 

 point, have greatly altered." 



More recent observations have brought out many new facts 

 about the magnetism of the Earth. Apparently the Earth is far 

 from being simply magnetized. The so-called magnetic poles 

 are over one thousand miles from the geographic poles; they are 

 not diametrically opposite, for a straight line drawn between 

 them passes some seven hundred and fifty miles from the center 

 of the Earth. Moreover, mathematicians tell us that the actual 

 magnetic poles are really not at the surface of the Earth at all, 

 but near its center. It was once thought that an iron ship should 

 not risk sailing near a magnetic pole, lest she should be unable 

 to free herself from the attraction, much as iron filings are fixed 

 to a bar magnet. This apprehension was groundless, as the real 

 poles are so near the center of the globe that iron weighs practi- 

 cally no more at the north magnetic pole than at the equator be- 

 cause of magnetic attraction. 



Then there are numerous areas on the Earth's surface, where 

 certain mineral deposits affect a compass in an anomalous way. 

 Some of these local disturbances are very intense, as in Kursk, 

 Russia, and in Iceland. In fact, these variations in magnetic 

 manifestations of subterranean masses have been used in mining 

 to locate ore. 



The forces directing the compass have also been found subject 

 to short-period changes, as distinct from the secular changes 

 mentioned above, such as the so-called annual, lunar, and diurnal 

 changes which have a degree of regularity. Besides these, times 

 of great activity on the surface of the Sun, as indicated by num- 

 ber of "sunspots," are in general times of an unsteady behavior 

 of the compass. When these disturbances become violent, they 

 are known as magnetic storms and may be so intense as to paralyze 

 cable and telegraph communication. 



