DEPARTMENT OF TERRESTRIAL MAGNETISM. 289 



of geographic interest was obtained on this trip. The probable non- 

 existence of Dougherty Island was confirmed and the geographic posi- 

 tion of Lindsay Island, as determined by the German exploring ship, 

 the Valdivia, in 1898, was verified. The interested reader may be 

 referred to the fuller account of the trip on pages 297 to 301. 



The Carnegie left Lyttelton again on May 17, 1916, bound for Pago 

 Pago, Samoa, arriving there June 7. Saihng from this port on June 

 19, she proceeded next to Guam in order to connect there with the 1907 

 work of the Galilee. The Carnegie was at Port Apra, Guam, from July 

 17 to August 6, during which period important shore observations and 

 instrumental comparisons were made. Leaving Guam August 6, the 

 vessel followed a track to San Francisco designed to secure as many 

 intersections as possible with the previous tracks of the Galilee and the 

 Carnegie, and to obtain magnetic observations in areas where additional 

 data are needed. The Carnegie arrived at San Francisco September 

 21, 1916. Here connection was made with the work of the Galilee 

 1905-1908. After again outfitting, the vessel on November 1 started on 

 her homeward trip around the Horn and via certain Atlantic ports to 

 Brooklyn, where she is expected in the fall of 1917. The total length 

 of the Carnegie's passages during the period November 1, 1915, to Octo- 

 ber 31, 1916, is 29,856 nautical miles. 



When the Carnegie returns to Brooklyn, magnetic data will have 

 been secured in nearly all the oceans traversed — in brief, the first 

 general magnetic survey of the oceans will have been nearly completed. 

 The Arctic and Antarctic regions, not accessible to the Carnegie 

 because she is not built for severe ice-conditions, must be covered in 

 some other manner. But much useful work remains for the Carnegie. 

 In the first place, it will be necessary to repeat magnetic observations at 

 intersections of the tracks of previous cruises in order to ascertain the 

 changes in the magnetic elements, so that mariners' magnetic charts 

 may always be kept up to date, and to provide the requisite data for the 

 scientific study of the causes of these changes. Beginning with 1918, 

 however, except in certain regions, it will be possible to reduce the 

 average daily routine of magnetic work and to devote the time gained 

 thereby to acquiring data in various other important lines of oceano- 

 graphic work and scientific inquiry. Indeed, had the Carnegie no other 

 useful mission, it would be a profitable investment to reserve her solely 

 for the determination of the annual changes in the Earth's magnetic 

 state. Frequently the errors found in the mariners' charts are attribut- 

 able largely to erroneous amounts of annual changes which the con- 

 structors of the charts, in the absence of accurate infonnation, adopted 

 in order to refer past magnetic data to a future date. 



But it is not merely the practical importance of magnetic data con- 

 cerning the Earth's magnetic changes that is here had in mind. The 

 acquirement of the scientific data necessary for the ultimate ascer- 



