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THE POPULAR SCIENCE MONTHLY 



Fig. 3. The Non-magxetic Yacht Cumcgie. 



downward at one pole, vertically upward at the other, and horizontally at 

 the equator. A dip needle, used to map the lines of force of the earth, 

 is shown on the screen. I have chosen for illustration an instrument 

 designed for use. at sea, on the non-magnetic yacht Carnegie (Fig. 3), 

 partly because the equipment used by Dr. Bauer in his extensive sur- 

 veys represents the best now in use, and also because I wish to contrast 

 the widely different means employed by the Carnegie Institution for 

 the investigation of solar and terrestrial magnetic phenomena. The 

 support of the dip-needle is hung in gimbals, so that observations may 

 be taken when the ship's deck is inclined. The smallest possible amount 

 of metal enters into the construction of this vessel, and where its use 

 could not be avoided, bronze was employed instead of iron or steel. She 

 is thus admirably adapted for magnetic work, as is shown by the observa- 

 tions secured on voyages already totaling more than 100,000 miles. 

 Her work is supplemented by that of land parties, bearing instruments 

 to remote regions where magnetic observations have never before 

 been made. 



The dip-needle clearly shows that the earth is a magnet, for it be- 

 haves in nearly the same way as the little needle used in our experi- 

 ment with the magnetized sphere. But the magnetic poles of the earth 

 do not coincide with the geograpliical poles. The north magnetic pole, 

 discovered by Eoss and last visited by Amundsen in 1903, lies near 

 Bafl^n's Bay, in latitude 70° north, longitude 97° west. The position 

 of the south magnetic pole, calculated from observations made in its 

 vicinity by Captain Scott, of glorious memory, in liis expedition of 

 1901-04, is 72° 50' south latitude, 153° 45' east longitude. Thus the 

 two magnetic poles are not only displaced about 30° from tlie geograph- 



