BAUER : ORIGIN OF THE EARTh'S MAGNETIC FIELD 3 



tion has been raised whether electrons can_ be acted upon by a 

 mechanical forCe, such as centrifugal force, it has not j^et been 

 experimentally settled in the laboratory, probably because of lack 

 of required sensibility of the instrumental appliances used, and 

 because of the limitations set upon the size and speed of rotation 

 of the body which can be experimented upon.^ Possibly in the 

 case of the Earth we have a body of sufficient size and angular 

 velocity to obtain appreciable effects. 



The rotation of the supposed electric charges with the Earth, if 

 distributed symmetrically about the Earth's center as Sutherland 

 premised, will result, as already pointed out, simply in producing 

 the so-called ''uniform magnetic field" whose equivalent intensity 

 of magnetization per unit of volume is constant thruout the 

 Earth's interior; this, however, we know not to be the case. The 

 hope of revealing the cause of the Earth's magnetic field appar- 

 ently centers in the discovery of the cause which makes the actual 

 field depart from the uniform or simple type. Hence, the key- 

 note of our line of investigation is the study of the variations — in this 

 particular instance the geographical variations of the character- 

 istic constants defining the Earth's magnetic field. 



The most important fact of terrestrial magnetism at this junc- 

 ture is one which I found in 1901,^ viz., that ''the value of the 

 magnetic moment is a maximum for the equatorial belt, and de- 

 creases steadily in both hemispheres with departure from the 

 belt." This law may be formulated mathematically thus: Let 

 X be the component of the Earth's total magnetic intensity 

 directed along a meridian, positive northward, and Z be the ver- 

 tical component directed positive downwards; if Dbe the magnetic 



8 Cf. Nichols, E. F., Die Moglichkeit einer durch zentrifugale Beschleunigung 

 erzeugten elektromotorischen Kraft. Phys. Zs. 7 Jhrg. No. 18, pp. 640-642. 

 Lebedew, P., Ueber die magnetische Fernwirkung rotierender Korper, Ann, d. 

 Phys. 1912, No. 14, 840-848. (This was this brilliant investigator's last work, he 

 having died before the appearance of his paper. He examined whether the Earth's 

 total magnetic field could be referred to effects attributable to centrifugal action 

 and supposed that the negative electron would be the one shoved outwards by 

 centrifugal action. He tested the question experimentally but reached no definite 

 results for the reasons already stated above.) 



^ Terr. Mag., 6: 22. 1901 and later investigations in same journal, 17: 85. 1912 

 and pp. 115-118. 



