OCEAN MAGNETIC OBSERVATIONS ON THE CARNEGIE. 1909-1916. 



EXPLANATORY REMARKS FOR FINAL RESULTS. 1909-1914. 



The same conventions, as nearly as possible, have been followed in the presen- 

 tation of the ocean magnetic results obtained on the Carnegie during the 5 years, 

 August 1909 to October 1914, as adopted for the land results in Volumes I and II. 



Stations. — It will be seen that the results are tabulated separately for each of the 

 cruises of the Carnegie, and for each ocean. Next under each cruise the stations or points 

 at which the observations were made are arranged chronologically, and they are numbered 

 accordingly. Thus for Cruise I, the stations are numbered beginning with ICI (Station 1, 

 Carnegie Cruise I). For Cruise II, the numbering proceeds chronologically, beginning with 

 ICII (Station 1, Carnegie Cruise II). Similarly for Cruise III, the first station is ICIII. 



Geographic positions. — The second and third columns contain, respectively, the lati- 

 tude and longitude (counted east from Greenwich), expressed in degrees and the nearest 

 minute of arc. The latitudes and longitudes for the points of observation at sea were 

 determined in accordance with the methods described on pages 225-231; La general they 

 may be regarded as correct within 2 or 3 nautical miles. When no astronomical observa- 

 tions were possible for several days the error in latitude or longitude may amount to 5, or 

 even 10 miles, dependent upon circumstances. The geographic positions of the harbor 

 stations are in general known within 1' of latitude and longitude. 



Date. — The date on which the magnetic observations were made is recorded in the 

 fourth column. The following abbreviations have been adopted for the months of the 

 year: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec. The year is indicated 

 at the head of the column. 



Magnetic elements.— The values of the magnetic elements (declination, inclination, and 

 horizontal intensity) will be found in the next columns as observed at the local mean time 

 (L. M. T.), expressed to nearest 0.1 of an hour, opposite each value. Occasionally it has 

 appeared desirable, where diurnal variation in dechnation was observed, as, for example, 

 in connection with the shore results on pages 296-309, or where numerous observations 

 were made during a certain interval, as during a vessel swing, to give the local mean times 

 of the beginning and of the end of the series, and to indicate for land results the number of 

 determinations from which the mean value is derived by a number inclosed in parentheses, 

 thus, 9 H to 11^3(7) is to be read "the mean is the result of 7 determinations made during 

 the interval 9^ to 11^3, local mean time, inclusive;" 6H to 20^3 (dv) is to be read "eye 

 readings of the suspended magnet were made regularly at short intervals from 6^1 to 20^3, 

 local mean time." The local mean times are given according to civil reckoning and are 

 counted from midnight as zero hour continuously through 24 hours; 16'', for example, 

 means 4 o'clock p. m. 



The ocean values of magnetic declination and of inchnation are given in degrees and 

 minutes of arc. No claim, however, is made that they are correct to a minute of arc. In 

 general the error in the tabulated value is about 5' to 10' or less; in some cases the error 

 may be more, dependent upon the severity of the conditions encountered dxu-ing the 

 observations. It was thought best to retain the original quantities resulting from the 

 computations until the various corrections, mentioned below, have been appUed. 



Only the mean quantities resulting from the observations with all instruments used 

 for any particular element are given. 



The values of the horizontal intensity, derived as exemplified on pages 216-220, 236, 

 and 247, with all instruments employed, are tabulated to the fourth decimal of the c. G. s. 

 unit of magnetic field intensity. In magnetic-survey work on land the fourth decimal is 

 often uncertain by one or more units, and in ocean work the error may be five or more 



257 



