DEPARTMENT OF TERRESTRIAL MAGNETISM. 1 



Louis A. Bauer, Director. 



GENERAL SUMMARY. 

 STATUS OF OCEAN WORK. 



The return of the Carnegie to Washington, her home port, on November 

 10, 1921, after the highly successful two-years' world cruise of 64,044 nautical 

 miles, has already been mentioned in the report for 1921; for the remainder 

 of the year she has been out of commission. Since beginning the ocean work 

 of the Department at San Francisco on August 3, 1905 — until June 1908 on 

 the chartered Galilee, and since 1909 on the Carnegie — 17 years have elapsed. 



In our early cruises there were disclosed in the mariners' charts giving the 

 compass direction (magnetic declination), errors amounting to 3°, 5°, 10°, 

 and even 16° in certain parts of the oceans, the errors often at times con- 

 tinuing in the same direction for several thousand miles. Equally serious 

 errors were found in the magnetic charts showing the inclination or dip of 

 the magnetic needle and the strength of the Earth's magnetic field; the 

 errors in inclination not infrequently amounted to over 10° and the values 

 of the Earth's magnetic intensity were found erroneous at times by amounts 

 reaching and even exceeding 10 per cent. 



When it is recalled that nearly three-fourths of the Earth's surface is 

 embraced by the ocean areas, it will be readily understood that lack of ac- 

 curate data for this portion of the globe has greatly retarded the settlement 

 of several of the chief problems of the Earth's magnetism. This unfortunate 

 state of affairs is now passed, thanks to the accumulated data obtained since 

 1905, both on sea and land, under the auspices of the Carnegie Institution 

 of Washington and of other organizations. With the aid of the data supplied 

 promptly from time to time to the leading hydrographic establishments, a 

 steady improvement in the magnetic charts has resulted. 



While there are still some large ocean areas, 500,000 to 1,000,000 square 

 miles, within which no recent accurate magnetic observations have been 

 made, it is believed that the chief conclusions regarding the general con- 

 stitution of the Earth's magnetic field which may result from an analysis of 

 the existing data now in progress will not be seriously affected. 



However, the Earth's magnetism is subject to ceaseless change, the laws 

 of which can not as yet be precisely formulated. We may determine from 

 our analysis of the existing data numerical quantities, the so-called "mag- 

 netic constants," which will define at some particular time, for example, a 

 mid-date between 1905 and 1921, the precise constitution and distribution 

 of the Earth's magnetic field, and will characterize, in a general way, the 

 magnetic and electric systems within and outside the Earth producing the 

 magnetic forces observed on the surface. But it does not seem likely that 

 we shall be able to determine from these "magnetic constants" for any 

 particular date the origin of the composing magnetic and electric systems. 

 It is believed, however, that some clues as to origin, or causes, will be obtained 

 from the character of changes which those "magnetic constants" will be found 

 to undergo from time to time. Those changes, as experience has shown, 



Address, Thirty-sixth Street and Broad Branch Road, Washington, D. C. 

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