PREVIOUS CRUISES AND PURPOSES OF CRUISE VII 9 



It may be appropriate here to give from eminent authorities 

 one or two quotations relating to terrestrial magnetism. Helm- 

 holtz and Maxwell, two of the greatest physicists, have considered 

 magnetism, next to gravity, as "the most puzzling of natural 

 forces." And Professor Fleming of England, referring to the 

 practical importance of research in this field, has said: "That 

 great empire which has its center in these islands (Great Britain), 

 but its dominions scattered over the distant seas, has been built 

 primarily on the art of navigation, in which the magnetism of the 

 Earth is a central fact. Neither its world-wide commerce, nor 

 the naval power which defends its coasts, could exist for a day 

 without the aid of the magnetic compass." 



The whole subject is thus exceedingly complex, and its com- 

 plexity has been increasingly made evident with the development 

 of observations and theories involving them offered in the past 

 century. To learn anything worth while of the nature of the 

 Earth's magnetic field, record of all these changes simultaneously 

 at many points on the Earth's surface was required. Accordingly 

 magnetic observatories have been set up throughout the world, 

 but these are not numerous and had therefore to be amplified by 

 establishing temporary stations in magnetically unexplored 

 countries. Furthermore, almost three-fourths the surface of the 

 globe is covered by the oceans, over which it was important to 

 collect information as well. 



This led to the plans made in 1904 and the formation of the 

 Department of Terrestrial Magnetism of the Carnegie Institution 

 of Washington under the energetic and resourceful directorship of 

 Dr. Louis A. Bauer for a world-wide magnetic and electric survey. 



The magnetic survey was begun immediately. Land parties 

 were organized to penetrate to the remotest corners of the Earth : 

 through the heart of Australia and the Sahara, over the top of 

 Central Asia, across the watersheds of South America, and through 

 the forests of the Congo, and on the northern plains of Canada. 

 Expeditions into polar regions were supplied with magnetic 

 observers. In fact, stations were occupied wherever camel or 

 canoe, mule or riverboat, motor or railway, could transport the 

 instruments. 



