BAUER: ORIGIN OF THE EARTH S MAGNETIC FIELD 



declination, /, the dip, and H, the horizontal intensity, then X = 

 H cos D, and Z ^H tan I. Obtain X and Z with* the aid of mag- 

 netic charts at equidistant points along parallels of latitude, say 

 every 10° apart in longitude; thus there will be 36 values of X and 

 of Z for each parallel covered by the charts, 60 N to 60 S, from 

 which the average values Xa and Z^ for each parallel may be 

 obtained. By operating with the average values we eliminate 

 the portion of the Earth's magnetic field asymmetrical about the 

 axis of rotation and if we, furthermore, combine the values for 

 corresponding parallels N and S, the asymmetrical portion about 

 the equator is also eliminated. The values of Xa and Z^ finally 

 obtained apply then only to the portion of the Earth's magnetic 

 field symmetrical about both the axis of rotation and the equator ; 

 they will be found given below as derived with the aid of all 

 the magnetic charts at present available (Sabine's for 1840-45; 

 Creak's 1880, and Neumayer's 1885). 



Values of the Rectangular Magnetic Components .Ya and Za and of the Charac- 

 teristic Functions, in C.G.S. Units, for Approximately the Year 1869. 



* Obtained graphically with the aid of values 5° N and S. 

 t Weight |. 



In whatever manner the magnetic field here considered may 

 have originated, we may write : 



Xa =/x {u) ■ sin u Z^ = 2/^ (m) • cos u (1) 



where u is the colatitude of the parallel considered and /x {u) , 

 /z {u) are functions of u, termed the ''characteristic functions," 

 as they contain the secrets of the origin of the field. Thus for 

 a simple uniform magnetic field (i.e., one for which the magnetic 



