ABSTRACTS 



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 this issue. 



TERRESTRIAL MAGNETISM.— Magnetic chart errors and secular 

 changes in the Indian Ocean. L. A. Bauer and W. J. Peters. 

 Journal of Terrestrial Magnetism and Atmospheric Electricity. 

 1911. 



This article gives a summary of the magnetic declinations together 

 with geographic positions as determined on the Carnegie during her 

 recent cruise from Cape Town to Colombo, Ceylon, and thence to Mau- 

 ritius, in April to August, 1911. The tables of values are supplemented 

 by the corresponding values scaled from a British Admiralty chart of 

 1907, the German chart of 1910, and the United States Hydrographic 

 Office chart of 1910, these values being referred approximately to the 

 time of observation by secular changes as indicated on the respective 

 charts. The differences between the Carnegie values and those of the 

 various charts are given. With the exception of a few values during the 

 first part of the cruise from Cape Town the chart errors are always nega- 

 tive, that is to say, the chart values are too low and hence a value of 

 west declination scaled from any of the charts mentioned must be 

 increased to make it correspond with that of the Carnegie. The errors 

 are unusually large, running up at times to 4°, and for one of the charts 

 is even as much as 6°. These chart errors, while partly due to the defec- 

 tive spacing of the lines of equal magnetic declination, are to be referred 

 chiefly to erroneous secular changes applied to the previous data on 

 which the charts depend. 



From a comparison of the Carnegie values with those of the German 

 Antarctic ship, the Gauss, made in 1903 by Dr. Bidlingmaier, secular 

 variation data may be obtained. The following values for secular change 

 result from the consideration of means at points common to the two 

 vessels. For the region of the mean south latitude 37° 29' and east 



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