44 



Land Magnetic Observations, 1905-10 



Magnetometer Corrections. 



The corrections of each instrument on adopted standards are determined at 

 Washington with every care, both before and after use in the field, following the 

 methods described on p. 19. Also, whenever opportunity permits, intercomparisons 

 are obtained in the field among observers of the Department and at observatories. 



The magnetometer corrections given in Table 3 depend generally upon com- 

 parisons involving two or more sets of at least twelve declination observations 

 and twelve horizontal intensity observations at three distances each. The accuracy 

 of the mean correction from the comparisons at any one station is usually of the 

 order 0'.l in declination and 0.00005/f in horizontal intensity. The tabulated 

 corrections are to be applied algebraically to observed values of the declination or 

 of the horizontal intensity; east declinations are reckoned as positive and west 

 declinations as negative; horizontal intensity is taken always as positive. 



Table 3. Magnetometer Corrections on Adopted Magnetic Standard Jar the Period, igos-igio. 



