16 



Land Magnetic Observations, 1911-13 



MAGNETIC STANDARDS ADOPTED. 



The standards adopted for reduction to a common basis of the results contained 

 in this volume are the same as those of Volume I, viz: In declination, C. I. W. 

 magnetometer No. 3 without correction; in horizontal intensity, C. I. W. mag- 

 netometer No. 3 with a correction of +0.00015// applied to observed values of H, 

 the horizontal intensity; in inclination, earth inductor No. 48, made by Schulze, 

 with a correction of 0'.5 applied to observed values of inclination, this correction 

 being based upon direct comparisons with the standard earth inductors at the 

 Potsdam and the Cheltenham magnetic observatories, 1907-1908. 



MAGNETOMETER CORRECTIONS. 



The corrections of each magnetometer on the adopted standard were deter- 

 mined at Washington, before and after use of the instrument in the field, and also, 

 whenever possible, in the field by means of intercomparisons with other outfits. 

 The accuracy of the mean correction is usually within about 0'.2 in declination and 

 about O.OOOli/ in horizontal intensity. The tabulated corrections are to be applied 

 algebraically, east declination being reckoned as positive and west declination as 

 negative; horizontal intensity is always taken as positive. 



The tabulated //-corrections are those actually applied in the final reductions 

 of the observations, except for magnetometers Nos. 12-23, for which the values 

 as given in Table 2 are the equivalent corrections on the basis of P' (see Table 1) 

 instead of P and Q originally used. 



'The values given in Volume I applying subsequent to alterations and repairs of March 1910 are erroneous and should 

 be amended according to the values here given. 



'Nos. 17, 19, 20, and 21 are magnetometers manufactured by the Department of Terrestrial Magnetism and are not the 

 same as the correspondingly numbered ones in Volume I, which are the property of the United States Coast and Geodetic 

 Survey. 



