52 NATIONAL ACADEMY OF SCIENCES 



As for the strength of the sun's field, only three preliminary 

 determinations have yet been made, with as many different lines. 

 Disregarding the systematic error of measurement, which is 

 still very uncertain, these indicate that the field-strength at the 

 sun's poles is of the order of fifty gausses (about eighty times that 

 of the earth). 



Schuster, assuming the magnetic fields of the earth and sun 

 to be due to their rotation, found that the strength of the sun's 

 field should be 440 times that of the earth, or 264 gausses.* This 

 was on the supposition that the field-strength of a rotating body 

 is proportional to the product of the radius and the maximum 

 linear velocity of rotation, but neglected the density. Before 

 inquiring why the observed and theoretical values differ, we may 

 glance at the two most promising hypotheses that have been ad- 

 vanced in support of the view that every large rotating body is a 

 magnet. 



On account of their greater mass, the positive electrons of the 

 neutral molecules within the earth may perhaps be more power- 

 fully attracted by gravitation than the negative electrons. In 

 this case the negative charge of each molecule should be a little 

 farther from the center of the earth than the positive charge. 

 The average linear velocity of the negative charge would thus 

 be a little greater, and the magnetizing effect due to its motion 

 would slightly exceed that due to the motion of the positive 

 charge. By assuming a separation of the charges equal to about 

 four-tenths the radius of a molecule (Bauer), the symmetrical 

 part of the earth's magnetic field could be accounted for as the 

 result of the axial rotation. f 



This theory, first suggested by Thomson, has been developed 

 by Sutherland, Schuster and Bauer. But as yet it has yielded no 

 explanation of the secular variation of the earth's magnetism, 

 and other important objections have been urged against it. 



* Bauer, by a similar method, obtained 306 gausses. 



t According to Bauer's view, in each molecule one charge occupies a larger volume than 

 the other, so as to make the volume densities of the two charges at the same point slightly 

 different. 



