REVIEWS 68 1 



revolution of the magnetic axis about the Earth's axis of rotation. (Were 

 the average annual rate of motion of the magnetic axis, as indicated dur- 

 ing the past 80 years, to continue unaltered, a complete revolution would 

 require about fifteen thousand years, or more. Shorter periods deduced 

 from analyses in which no account is taken of possible change in intensity 

 of magnetization, besides change in direction of magnetization, or 

 obtained from a discussion of the secular change in limited regions of 

 the globe, evidently cannot be regarded as pertaining to the Earth's 

 field as a whole.) 



"d. The average equivalent intensity of magnetization of the Earth 

 has been steadiFy diminishing during the past 80 years at the average 

 annual rate of about 1/1500 part. How long it will continue to diminish, 

 whether there will be a time of no change, or whether it will later increase, 

 are questions that cannot be answered at the present time. (Whether 

 the annual rate of loss is actually variable, as would apparently be indi- 

 cated on the basis of the magnetic charts of 1885 and 1 840-1 845, is 

 another matter which must await completion of additional analyses to 

 be made for epochs for which magnetic data of known reliability are 

 available.) 



"e. A suggestive effect, dependent apparently upon the distribution 

 of land and water, has been disclosed, namely, that the average equivalent 

 intensity of magnetization for corresponding parallels north and south, 

 is generally larger for the land-predominating parallel than for the ocean- 

 predominating parallel. 



"f. For 1922 we have for the Earth's uniform internal magnetic 

 field, as deduced from magnetic observations over 86 per cent of the 

 Earth's surface (60° N. to 60° S.), the following data, which it is expected 

 will be only slightly modified by the final analysis, R being the Earth's 

 mean radius (6.37X10^ cm.): 



M^ = Component of magnetic moment parallel to axis of rotation 



= 0.3047 i?3= 7.^8X10^5 C.G.S. 

 Me = Equatorial component of magnetic moment 



= o.o6i8i?-5 = i.6oXio^s C.G.S. 

 M ^Resultant magnetic mom.ent^ = o.3io9i?3 = 8.o4Xio^5 C.G.S. 

 M^ = 4.93 Me. 



"If the Earth's magnetism were distributed uniformly throughout 

 its volume, as it probably is not, the average intensity of magnetization 

 would be 0.074 C.G.S. The magnetic axis intersects the North Hemi- 

 sphere in latitude 78° 32' N. and longitude 69° 08' W. of Greenwich." 



