OCEAN MAGNETIC OBSERVATIONS ON THE GALILEE, 1905-1908. 



EXPLANATORY REMARKS. 

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

 tation of the ocean magnetic results obtained on the Galilee during the three years 

 August 1905 to May 1908 as adopted for the land magnetic results in Volumes I 

 and II. 



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

 three cruises of the Galilee, all of which were in the Pacific 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 from 

 1 G I (Station 1 Galilee Cruise I) to 104 G I (Station 104 Galilee Cruise I) inclusive. Simi- 

 larly for Cruise II, the numbering proceeds chronologically from 1 G II (Station 1 Galilee 

 Cruise II) to 125 G II (Station 125 Galilee Cruise II). The stations for Cruise III proceed 

 chronologically from 1 G III to 213 G III. 



Geographic Positions. — The second and third colunms contain, respectively, the 

 latitude and longitude (counted east from Greenwich), expressed in degrees and minutes, 

 to 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 58-60 ; in general 

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

 observations were possible for several days, the error in latitude, or in longitude, may 

 amount to 5 or even 10 miles, depending upon circumstances. The geographic positions 

 of the harbor stations are in general known within 1 minute 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 indi- 

 cated at the head of the colunm. 



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

 and horizontal intensity) will be found in the next columns, preceded in each case by the 

 local mean time (L. M. T.) of observation, expressed to nearest 0.1 of an hoiu*. In cases 

 where the observations which make up the mean value are numerous and are scattered 

 over various parts of the day, so that the mean may be practically taken as the mean of 

 day, the local mean times are replaced by the word "various"; in such cases the number 

 of determinations from which the mean value is derived is indicated for the shore results 

 (pp. 105-110), in general, by a number inclosed in parentheses. Where numerous obser- 

 vations were made during a certain interval, as during a vessel swing, it has appeared 

 desirable to give the local mean times of the beginning and of the ending of the swing. 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 inclination are given in degrees and 

 minutes, to the nearest minute 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 15' to 20', depending on the severity of the conditions 

 encountered during the observations. It was thought best to retain the original quantities 

 resulting from the computations until the various corrections, mentioned below, had been 

 appUed. The error of a harbor result, usually depending upon extensive observations 

 during the swing of the vessel, is generally not over 5', and may be less. Only the mean 



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