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THE POPULAR SCIENCE MONTHLY 



satisfactory indications of the field. But with the higher dispersion 

 of the third order eleven independent determinations, made with every 

 possible precaution to eliminate bias, show opposite displacements in 



8 90° Equator N 90° 



^j M ^ ^ :^, 



Fig. 15. The curve represents the theoretical variation of the displacements ol 

 spectrum lines with the heiiographic latitude. The sun is assumed to be a magnetized 

 sphere with its magnetic poles coinciding with the poles of rotation. The points 

 represent mean values of the observed displacements. Vertical scale : 1 square = 

 0.001 mm. = 0.0002 Angstrom. 



the northern and southern hemispheres, decreasing in magnitude from 

 about 45° north and south latitude to the equator. Three of these 

 determinations were pushed as close to the poles as conditions would 

 permit, and the observed displacements may be compared with the the- 

 oretical curve (Fig. 15). 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 mag- 

 netic 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 rotation, 

 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 tempera- 

 ture, 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 mag- 

 netic polarity. 



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

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

 garding the systematic error of measurement, which is still very uncer- 

 tain, these indicate that the field-strength at the sun's poles is of the 

 order of 50 gausses (about eighty times that of the earth). 



* Contributions from the Mount Wilson Solar Observato-ry, No. 71. 



