REVIEWS 



Chief Results of a Preliminary Analysis of the Earth's Magnetic 

 Field for ip22. By Louis A. Bauer. Terrestrial Magnetism 

 and Atmospheric Electricity, Vol. XXVIII, Nos. i and 2 

 (March-June, 1923), pp. 1-28. 



SUMMARY OP CHIEP CONCLUSIONS 



"27. The chief conclusions reached in the present paper are as follows: 



"a. It is necessary to recognize that the Earth's total magnetic field 

 at any one time is apparently composed, to the extent of about 94 per 

 cent, of an internal magnetic potential system, /, and to the extent of 

 about 6 per cent, of an external magnetic potential system, E, plus a 

 non-potential system, N 



"b. Instead of the three systems, /, E, N, the exact evaluation of 

 each of which rests somewhat on assumption as to the character of the 

 causes producing the observed magnetic field of the Earth, we may say 

 that in order to represent satisfactorily the observed magnetic data, it 

 is necessary to recognize the existence of three distinct systems, namely, 

 the X, Y, Z systems. The X-system is responsible for the total compon- 

 ent acting on the magnetic needle in the direction positive towards geo- 

 graphic North; the F-system, for the total component in the direction 

 positive towards geographic East; and the Z-system, for the total com- 

 ponent acting in the vertical direction positive towards the nadir. 



"c. It must be recognized that the magnetic secular- variation system 

 is as complex as the Earth's total magnetic field existing at any one time, 

 and that in addition to changes in the direction of magnetization with 

 the lapse of time there is also a change in the average equivalent intensity 

 of magnetization. The magnetic axis of one component of the total 

 secular-variation system may show a reverse motion in latitude and 

 longitude to that shown by another component. On the whole, as a 

 resultant effect, it would seem that the north end of the axis of the Earth's 

 internal magnetic field during the past 80 years has been moving slowly 

 towards the west, and apparently at the same time slowly towards the 

 equator. It is not possible to speak at present of any period of complete 



680 



