MOUNT WILSON OBSERVATORY. 



191 



tions of a considerable number of spots, gives the approximate in- 

 clination of the lines of force in various parts of the umbra and penum- 

 bra. Thus we find, from 105 observations of 61 spots made by Messrs. 

 Joy and Nicholson, the accompanying positions of the neutral line 

 and the corresponding inclinations of the lines of force (taken as 

 normal to the Hne of sight passing through the neutral line) : 



The position of the neutral line is given in terms of a scale in which 

 1 represents the outer edge of the penumbra (toward the limb) , 3 the 

 outer edge of the umbra, and 5 the center of the umbra. 



These results indicate that the lines of force at the center of the 

 spot lie in a plane passing through this center and the sun's axis. 

 They do not show, however, whether these central lines of force are 

 normal to the sun's surface or incUned toward the north or south. 



The latter question can be answered by determining the relative 

 intensities of the n- and p-components of a Zeeman triplet in different 

 parts of a spot observed near the center of the sun. The results of 

 such observations vary greatly among themselves, but in many spots 

 the 7?-component is strong even at the center of the umbra when the 

 spot is near the center of the sun. In such a case the central lines of 

 force must be considerably inclined toward the north or south. In 

 spite of the many anomalies hitherto encountered the investigation is 

 being continued in the hope of finding a general law governing the 

 inclination of the lines of force. 



RELATION BETWEEN FIELD-STRENGTH AND SIZE OF SUN-SPOTS. 



Preliminary observations made some years ago reveal a definite 

 correlation betv/een the area of a sun-spot and the strength of the 

 accompanying magnetic field. Mr. Nicholson has studied the relation 

 from much more extensive data, including more than 300 spots, and 

 finds that the field increases rapidly with the area in the case of small 

 spots. For larger spots the increase is much less marked and the 

 field seems to approach asymptotically an upper limit in the neigh- 

 borhood of 3,500 or 4,000 gausses. These results are based upon the 

 iron X 6173, of Rowland intensity 5. 



GENERAL MAGNETIC FIELD OF THE SUN. 



The preliminary results of a study of the Zeeman effect due to the 

 sun's general field were published in Contribution No. 71, and have 



