PROCEEDINGS OF THE ACADEMY AND AFFILIATED 



SOCIETIES 



PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 804th meeting of the Society was held at the Cosmos Club, 

 March 30, 1918; Vice-President Humphreys in the chair; 53 persons 

 present. The minutes of the 803d meeting were read in abstract and 

 approved. 



Mr. D. L. Hazard presented the first paper, on The magnetic survey 

 of the United States. The magnetic survey of the United States may be 

 said to have had its beginning in 1843, when a plan for the reorgani- 

 zation of the survey of the coast was adopted wliich provided for making 

 magnetic observations, but progress was slow up to 1899, because of 

 lack of funds. Beginning with that year an annual appropriation of 

 $25,000 has made possible a systematic survey of the whole country. 

 The plan under which the work has been executed provides for mag- 

 netic observations at places 30 to 40 miles apart on the average; a sub- 

 sequent more detailed investigation of areas of local disturbance; the 

 occupation of a sufficient number of repeat stations to determine the 

 secular change of the magnetic elements; and the operation of magnetic 

 observatories. 



The work has progressed to the point where observations have been 

 made at all but about 150 county seats, results being available for about 

 5,500 stations, and attention is now being directed more especially to 

 the investigation of areas of local disturbance and the occupation of 

 repeat stations. Magnetic surveys have been, made of Porto Rico, 

 Hawaii, and the Philippines and the accessible portions of Alaska. 

 Observations at sea have been made on some of the vessels of the Survey. 

 Meridian lines have been established at many stations, and at most of 

 the others the necessary information has been secured to enable local 

 •surveyors to test their compasses. 



The results of the survey have been published from time to time, 

 as the work progressed, in the form of magnetic tables and magnetic 

 charts, the latest publication, just issued, being Magnetic Tables and 

 Magnetic Charts for 1915, containing the accumulated results to the 

 end of 1915. 



While the survey had its origin in the needs of the navigator and 

 surveyor, yet the importance of the scientific side has been kept in 

 view from the outset and due attention has been given to securing the 

 data needed for a comprehensive study of the earth's magnetism, with 

 a view to determining its origin and the cause of its fluctuations. 



The paper was discussed by Messrs. Bauer and Humphreys. 



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