DEPARTMENT OF TERRESTRIAL MAGNETISM, I97 



ing error in a ship's course based on the present mariners' charts may be 

 cumulative and uhimately reach a considerable amount. The maximum chart 

 error at any one point may be from 1.3° to 2.6°, according to the chart used. 



The average chart error (sign not being considered) for magnetic dip 

 approximates 1.5° to 2° the maximum error for the British chart being 2.5° 

 and that of the German 4.4°. The British chart gives, in general, too small 

 dips and the German too large ones. 



The average chart errors for magnetic horizontal intensity, disregarding 

 sign, approximate 8 units in the third decimal C. G. S. ; the maximum error 

 is about 15 units for either British or German chart. For the greater part, 

 both charts give, in general, too high values. 



The Carnegie's first cruise covered about 8,000 nautical miles and extended 

 from September i, 1909, to February 1910. On June 20, 1910, she began 

 her second cruise, which will extend around the globe, with an aggregate 

 length of about 65,000 nautical miles and requiring about 3 years for com- 

 pletion. Special tests made in Gardiner's Bay, off Long Island, again showed 

 that, with the appliances and methods used aboard the Carnegie, the mag- 

 netic elements can be determined with an accuracy sufficient for all purposes, 

 practical as well as scientific. 



Leaving Greenport, Long Island, June 29, she arrived off Port Mulas, 

 Porto Rico, July 24. On this trip errors in the mariners' compass charts of 

 2° to 2.5° in the North Atlantic were once more revealed, as also similar 

 errors to those found on the first cruise in the dip and the magnetic force. 

 Reviewers of the work already accomplished by the Carnegie have made the 

 statement that even if this vessel should do nothing more she has already 

 justified her existence. 



The projected circumnavigation cruise of the Carnegie can be briefly indi- 

 cated by the following ports to be visited : Greenport, Long Island ; Vieques, 

 Porto Rico, where she arrived July 24 ; Para, where she arrived September 

 24, and Rio de Janeiro (November 1910) ; Montevideo and Buenos Ayres 

 (December 1910) ; Tristan da Cunha and Cape Town (March 191 1) ; Co- 

 lombo (Ceylon) and Bombay, Mauritius, and Batavia (October 191 1) ; 

 Manila (December 191 1) ; Samoa (March 1912) ; Acapulco, Mexico (June 

 1912) ; Cape Horn and South Georgia Island (November 1912) ; Cape Town 

 (January 1913) ; Vieques, Porto Rico (April 1913) ; Greenport, Long 

 Island (June 1913), 



On the accompanying map, the status of the magnetic work accomplished 

 both on land and ocean by the Department up to October 31, 1910, is shown 

 in red. The cruises of the Galilee in the Pacific Ocean, 1905-08, and of the 

 Carnegie in the Atlantic Ocean, 1909-10, are shown by full red lines. The 

 uncompleted portion of the circumnavigation cruise of the Carnegie is shown 

 by broken red lines (return portion is indicated by dots and dashes). 



Besides the important results in magnetism obtained by the Carnegie, there 

 has also been acquired other information of interest to the mariner, viz, data 

 for testing and revising the corrections which must be applied, on account 



