52 Land Magnetic Observations, 1905-10 



smaller number of cases, the horizontal intensity from the observed total intensity 

 and inclination, the so-obtained values being italicized in order to reveal their 

 derivation. 



It was also decided to publish the intensities in C. G. S. units, one C. G. S. unit 

 being designated by capital gamma, T. In magnetic survey work the fourth deci- 

 mal is often uncertain by one or more units and in ocean work the error may be 

 five or more units in this decimal place. For these reasons it appears unadvisable 

 in magnetic survey work to adopt so small a unit as a small gamma, 7 = 10~^ C. G. S. 

 unit = 10~^r; it would be necessary otherwise at times to round out the observed 

 value by one or more zeros. This is avoided by the use of the larger unit; if the 

 conditions under which an intensity result was obtained were such as not to warrant 

 publishing the fourth or fifth decimal, this can be shown by stopping with the 

 decimal deemed certain; some such cases will be found in the Table. In general, 

 however, as will be seen, the value to the fifth decimal is given, but it should be 

 understood that no claim is made for the correctness in all cases of the last figure; 

 it has been retained here primarily in order that when all reductions to common 

 epoch have been applied on account of the magnetic variations, an error of a unit 

 in the fourth decimal, due purely to computation, will not enter. 



The first column in the Table is headed "Station"; this gives the name of place 

 at which the magnetic elements were observed, the spelling adopted being in ac- 

 cordance with the most reliable information at hand and conforming as far as 

 possible to local usage. The next column gives the geographical position, latitudes 

 and longitudes, as derived in most cases from the observer's local astronomical 

 observations following the methods already described. When the latitudes are 

 the result of fairly complete circummeridian observations of the Sun, or the mean 

 of several re-occupations of the same station, or are derived from reliable large 

 scale maps, then they are given to the nearest O'.l, though it should be distinctly 

 understood that this accuracy is not guaranteed, as even for these cases the error 

 may be as much as 0'.5 and even in some instances a whole minute of arc. When 

 the latitudes are given only to the nearest minute, there were either no astronomical 

 determinations or they may have been incomplete or defective; these values are 

 usually taken from standard atlases and for some regions may be in error by several 

 minutes. Owing to the numerous sources of error of a longitude determination and 

 especially because of the uncertainty in more or less unexplored countries of the 

 adopted chronometer correction on standard time, the longitude in no instance is 

 tabulated closer than to the nearest minute of arc. Usually it is derived from the 

 observer's astronomical observations. Considerable use was also made of reliable 

 large scale maps, whenever available, and of standard atlases; the values in regions 

 but slightly surveyed may be out sometimes by several minutes. 



The date on which the magnetic observations were made will be found 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 

 values of the magnetic elements will be found in the next columns as observed at 

 the local mean time opposite each value and expressed to nearest 0.1 of an hour. 



