156 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1913. 



Three of these determinations were pushed as close to the poles as 

 conditions would permit, and the observed displacements may be 

 compared with the theoretical curve (fig. 14). In view of the very 

 small magnitude of the displacements, which never surpass 0.002 

 Angstroms, the agreement is quite as satisfactory as one could expect 

 for a first approximation. 



The full details of the investigation are given in a paper recently 

 published.^ The reader will find an account of the precautions taken 

 to eliminate error, and, I trust, no tendency to underestimate the 

 possible adverse bearing of certain negative results. It must remain 

 for the future to confirm or to overthrow . the apparently strong 

 evidence in favor of the existence of a true Zeeman effect, due to the 

 general magnetic field of the sun. If this evidence can be accepted, 

 we may draw certain conclusions of present interest. 



Taking the measures at their face value, they indicate that the 

 north magnetic pole of the sun lies at or near the north pole of rota- 

 tion, while the south magnetic pole lies at or near the south pole of 

 rotation. In other words, if a compass needle could withstand the 

 solar temperature, it would point approximately as it does on the 

 earth, since the polarity of the two bodies appears to be the same. 

 Thus, since the earth and sun rotate in the same direction, a negative 

 charge distributed through their mass would account in each case 

 for the observed magnetic polarity. 



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

 minations have yet been made, with as many different lines. Disre- 

 garding 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 50 gausses (about 80 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 sup- 

 position that the field strength of a rotating body is proportional to 

 the product of the radius and the maximum linear velocity of rota- 

 tion, but neglected the density. Before inquiring why the observed 

 and theoretical values differ, we may glance at the two most prom- 

 ising hypotheses that have been advanced 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 powerfully 

 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 



^Contributions from the Mount Wilson Solar Observatory, No. 71. 



