STATUS OF THE GENERAL MAGNETIC SURVEY OF OCEAN AREAS. 



On Plate 20, the cruises of the Galilee, 1905-1908, and the Carnegie, 1909-1916 

 (September), are shown, the former by black Unes and the latter by red ones. The red 

 dots indicate the land magnetic stations (about 3,500) estabUshed by the Department of 

 Terrestrial Magnetism from 1905 to October 1916; they are distributed over 115 different 

 countries and island groups, being located especially in regions where no magnetic 

 results, or but an insufficient number, had been obtained previously. The red dots in 

 Hudson Strait and Hudson Bay represent the points at which magnetic observations were 

 obtained by the Department in 1914 on the chartered gasoline schooner, the George B. Cluett. 



The dhections in which the various passages were made are indicated by arrow-heads. 

 The Ai-abic numbers, 1, 2, and 3, designate, respectively, the three cruises of the Galilee 

 (August 1905 to May 1908) ; the Roman numbers, I, U, III, and IV, refer to the four 

 cruises of the Carnegie carried out from August 1909 to September 1916. Plate 20 thus 

 shows the status of the general magnetic survey of ocean areas as represented by the 

 cruises of the two vessels, the Galilee and the Carnegie, from August 1905 to September 

 1916. 



Table 72 shows for each cruise of the Galilee and of the Carnegie the number of days 

 at sea,^ the length of the cruise in nautical miles, and the nmnber of observed values of the 

 magnetic dechnation, incUnation, and intensity of the Earth's magnetic field. The subse- 

 quent colunms give the average time-intervals, as well as the average distances apart, 

 between the observations. The entries in the bottom row of the table summarize the work 

 of the two vessels from August 1905 to September 1916. It will be seen that the aggre- 

 gate length of all the cruises of the Galilee and Carnegie thi'ough September 1916, is 224,449 

 nautical miles. The length of the return passage (see broken red Unes on Plates 23 and 24) 

 from San Francisco to Brooklyn, November 1916 to October 1917, is expected to be about 

 30,600 miles. Accordingly, when the present cruise (No. IV) of the Carnegie has been 

 completed, namely, by the end of 1917, the aggregate length of the cruises of the two ves- 

 sels will be about 255,000 nautical miles. 



It is seen from Table 72 that the average time-intervals and average distances apart 

 for the Galilee work have been decreased by about 45 per cent in the Carnegie work. The 

 increased efficiency, or productiveness, has resulted from the fact that the Carnegie is a 

 non-magnetic vessel and because of the steady improvement in the instrumental appliances 

 and observational methods. 



'In the case of the Galilee work, to the number of days at eea were added the daya spent in the harbor-awings. 

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