THE SEMI-CENTENNIAL ANNIVERSARY 39 



When the plate is tapped, to relieve the friction, the particles 

 fall into place along the lines of force, revealing a characteristic 

 pattern of great beauty. A small compass needle, moved about 

 the sphere, always turns so as to point along the lines of force. 

 At the magnetic poles, it points toward the center of the sphere. 

 Midway between them, at the equator, it is parallel to the 

 diameter joining the poles. 



As the earth is a magnet, it should exhibit lines of force 

 resembling those of the sphere. If the magnetic poles coincided 

 with the poles of rotation, the north-seeking end of a freely 

 suspended magnetic needle should point vertically downward at 

 one pole, and vertically upward at the other, and the needle 

 should be horizontal 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 be- 

 cause the equipment used by Dr. Bauer in his extensive surveys 

 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 obser- 

 vations 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 observations 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 behaves in nearly the same way as the little needle used in our 

 experiment with the magnetized sphere. But the magnetic poles 

 of the earth do not coincide with the geographical poles. The 

 north magnetic pole, discovered by Ross and last visited by 

 Amundsen in 1903, lies near Baffin's Bay, in latitude 70 north, 



