MOUNT WILSON SOLAR OBSERVATORY, 



205 



The table shows the reversal of the sign of the displacement in 

 the opposite hemispheres of the sun and the decrease in the values 

 from 45° north and south latitude toward the equator and the poles. 

 When these observations are plotted, they are found to agree very 

 closely with the theoretical curve described below. 



Since the conclusion of the preliminary investigation with the three 

 lines mentioned, Mr. van Maanen has measured other selected lines 

 with the results indicated in the following table : 



Seven lines in this table, which are indicated by asterisks, show a 

 marked preponderance of displacements of the right sign. Accor- 

 dingly, an approximate reduction of these observations was made, 

 with the results indicated in the ninth column of the table, which gives 

 the maximum of the displacement curve expressed in thousandths 

 of a millimeter. A large nuniber of other lines are now being measured, 

 in order to determine what elements show the effect and to give a 

 preliminary determination of its magnitude at different levels in the 

 solar atmosphere. As the work of measurement is slow and tedious, 

 some time may elapse before the definitive investigation can be begun. 



It appears to be quite safe to conclude, from the extensive series 

 of measurements already completed, that the sun is a magnet, with 

 poles falling at or near the poles of rotation. An approximate de- 

 termination of the strength of the magnetic field gives a value of 

 about 50 gausses for the vertical intensity at the sun's poles. Hence 

 the sun's field, at the level in question, is some 80 times as intense as 

 that of the earth. As for the polarity of the sun, it is interesting to 



