434 



Reports on Special Researches 



ANNUAL-CHANGE DATA AT PORTS. 



From the shore magnetic observations at ports of call of the Galilee and the Carnegie, 

 the results of which are given on pages 105-110 and 296-310, the average annual changes of 

 the magnetic elements may be determined at all ports at which the observations have been 

 repeated at various times, which is often the case. These shore repeat-observations will be 

 utiUzed in conjunction with the usual land magnetic results, the discussion of which is to be 

 undertaken in a subsequent volume. 



Data for Gardiners Bay and Greenport, Long Island. 



It will be of interest here to obtain some idea of the accuracy attainable in the deter- 

 mination of secular changes with the appUances and methods used in the Carnegie work, 

 when the observations are made under the most favorable conditions. For this purpose, 

 the results of observations during swings of the Carnegie in Gardiners Bay, 1909-1915, are 

 selected, and comparisons are made with the results of shore observations during 1909-1914 

 at Greenport, about 8 miles distant from the place of swing, obtained by the Carnegie 

 observers using the latest t>T)es of magnetic instruments for land work. The results of the 

 observations for Gardiners Bay will be found in the tables of ocean results, pages 261-288, 

 and those for Greenport on pages 298-300. All the results have been corrected for diurnal 

 variation with the aid of the records of the magnetic observatory of the United States Coast 

 and Geodetic Survey at Cheltenham, Maryland, a factor having been apphed to refer the 

 corrections to the observation-stations, Gardiners Bay and Greenport. 



Table 99.— Results of Magnetic Observations in Gardiners Bay, 1909-1915. 

 (Latitude, 41° 06' N; longitude, 72° 13' W.) 



Table 100. — Results of Magnetic Observations at Greenport, Long Island, 1909-1914. 

 (Latitude, 41° 06:4 N; longitude, 72° 22' W.) 



