CHARTING THE OCEANS FOR SAFE NAVIGATION 67 



the Navy in 1882. 



With the passing of the years, the scientific study of the earth's 

 magnetic field was recognized as being of major importance. One 

 component, the variation, or magnetic declination, of the earth's 

 magnetic field, is displayed on all nautical and aeronautical charts. 

 Other components needed for purposes of compass adjustment 

 and compensation, degaussing, magnetic guidance, and numerous 

 other military, commercial, and scientific uses, are charted in a 

 series of world charts. 



Production of world magnetic charts by the Navy stems directly 

 from its basic mission. The series of charts provides compre- 

 hensive information on each magnetic element, namely, dip or 

 inclination (I), horizontal intensity (H), vertical intensity (Z), 

 total intensity (F), and magnetic variation (or declination) (D). 

 Each chart, in addition to displaying isopleths of the charted 

 element, also contains isoporic or annual change lines which make 

 possible correction for epochs other than those for which the 

 isomagnetic lines are shown. 



Under contract with the Navy, the U. S. Coast and Geodetic 

 Survey compiles world magnetic charts incorporating data from 

 Project MAGNET. These charts are then published by the U. S. 

 Naval Oceanographic Office. The magnetic information for the 

 1965 epoch charts was compiled by analytical techniques, using 

 modem high-speed computers in place of former graphic methods. 

 A more accurate and more scientifically acceptable portrayal of 

 the strength and direction of the geomagnetic field resulted. 



At the present time, 29 magnetic charts are published by the 

 Navy and are on sale to the public. Because of the constantly 

 changing nature of the earth's magnetic field, new editions of 

 charts showing magnetic declination are published every five 

 years; new editions of charts showing magnetic inclination, hori- 

 zontal intensity, vertical intensity, and total intensity are published 

 every ten years. 



SPECIAL PURPOSE CHARTS 



The tremendous increase in activity in the marine sciences and 

 in the sophistication of weapons systems and military operations 

 has created an unprecedented demand for various types of special 



