I9I2.] MAGNETIC CHARTS OF THE INDIAN OCEAN. 241 



13' per year. The charts give secular changes of only about one 

 fourth of these amounts, so that the error of reduction in but ten 

 years amounts to almost 2°. It is doubtless due to these large 

 secular changes disclosed in the Indian Ocean, and especially their 

 rapid variation with geographic position, that the large errors men- 

 tioned have crept into the charts. 



The errors in the other magnetic elements, while of less impor- 

 tance to the mariner, are of consequence to theoretical investigations 

 regarding the earth's magnetism. In the magnetic dip. the errors 

 on the present cruise have amounted at times to 4°, and in the hori- 

 zontal intensity to about one-twentieth part. While some of the 

 results derived from previous analyses of the earth's magnetic field 

 have pointed to the possibility of large and more or less systematic 

 chart errors, it was not suspected that they would reach the magni- 

 tude disclosed by the work of the Galilee and of the Carnegie. 



The Carnegie is at present making a circumnavigation cruise and 

 is expected back in New York towards the end of 1913, having left 

 the same port in June, 1910. Up to February i, 1912, this vessel 

 had already covered about fifty thousand miles. She left Manila 

 on March 23, in command of ]\Ir. W. J. Peters, bound for the Fiji 

 Islands. 



Owing to the non-magnetic structure of the Carnegie and the 

 absence in consequence of any deviation corrections, it is possible 

 to obtain and communicate results expeditiously. The data are 

 promptly transmitted to the chief hydrographic establishments issu- 

 ing magnetic charts in order to enable them to make the necessary 

 corrections from time to time. 



