DEPARTMENT OF TERRESTRIAL MAGNETISM.* 



L. A. Bauer, Director. 

 GENERAL SUMMARY. 



The event of chief importance in the pubUcation work of the Depart- 

 ment is the completion of Volume III of its Researches. This volume 

 contains the final results of the ocean magnetic work, 1905-1914, and 

 the preliminary results for the present cruise of the Carnegie, from 

 March 1915 to September 1916; also, accounts are given of various 

 investigations, especially with regard to observational methods and 

 newly designed instruments for the ocean work. 



The three cruises of the Galilee, 1905-1908, aggregated 63,834 

 nautical miles, and the four cruises of the Carnegie, 1909 to 1916 

 (September), 160,615nautical miles. The aggregate length of the cruises 

 of the two vessels, 1905 to 1916 (September), is, accordingly, 224,449 

 nautical miles. On the average, magnetic observations at sea have 

 now been made at points 100 to 150 miles apart, and the results will be 

 found in the ''Tables of Results" given in Volume III. The various 

 tables contain the results for 443 stations of the Galilee work and for 

 2,807 stations (to September 21, 1916) of the Carnegie work; hence, 

 together, for 3,250 stations to September 21, 1916. In addition, mag- 

 netic observations have been made at numerous shore stations. 



The great advantage of having a non-magnetic ship, like the Carnegie, 

 is made very apparent in the comparison of the work of the Galilee and 

 the Carnegie, both as to accuracy and rapidity of work. While the 

 operating expenses of the chartered vessel, the Galilee, were less than 

 those of the Carnegie, the difference was more than made up by the 

 fewer results during a given period and the increased cost of the office 

 work for the Galilee, because of the need of determining deviation 

 corrections, which is not necessary for the Carnegie. 



The general plan according to which the magnetic survey of the globe 

 is being carried out provides not only for securing magnetic data in aU 

 regions where needed, but also for the determination of the average 

 annual changes, the so-called "secular changes" in the Earth's magnetic 

 state. On the oceans this is done by making observations at intersec- 

 tions with previous cruises of the Galilee and the Carnegie, or with the 

 tracks followed by the vessels used in recent Antarctic expeditions. 

 L"p to October 1, 1916, such repeat observations have been made at 

 about 85 intersections of cruises of the Galilee and the Carnegie, the 

 average time-mterval being approximately 5 years. In addition, the 

 secular changes have been determined by the observers at many points 

 on land (islands and continents) . 



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



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