228 CARNEGIE INSTITUTION OF WASHINGTON. 



peculiarities of the Zeeman effect, demanding new theoretical and 

 laboratory studies, have been revealed (p. 236). The most striking 

 result, however, is another step toward the recognition of the true law 

 of polarities of sun-spots in the northern and southern hemispheres of 

 the sun. 



The last annual report recorded the detection of an abrupt reversal 

 in the magnetic polarities of spots at the sun-spot minunum. This 

 would probablj'^ indicate, if the magnetic fields are due to vortices, that 

 the vortices of spots occurring before and after the minimum whirl in 

 opposite directions. As the spots of the new cycle appear in high lati- 

 tudes, while those representing the end of the old cycle are close to the 

 equator, it seemed easiest at first to assume that an effect of latitude 

 was in evidence. But as the cycle has progressed, many spots appear- 

 ing in low latitudes have been found to have the same polarity as those 

 in the higher zones. It now remains to be seen whether a second re- 

 versal of polarity will occur at the spot maximum, and to interpret the 

 bearing of these unexpected phenomena on the nature of spots and the 

 cause of the sun-spot cycle (p. 237). 



The excellent series of photographs of the sun's higher atmosphere, 

 obtained since the completion of the 13-foot spectroheUograph, has 

 rendered possible a statistical study of the direction of whirl in the 

 hydrogen vortices. This has brought to light the fact that this direc- 

 tion did not reverse at the sun-spot minimum. If these apparent 

 vortices were due to the effect of the magnetic fields in spots on the 

 ionized hydrogen above them, their direction of whirl should have 

 reversed simultaneously with the reversal of polarity of the magnetic 

 fields below. But no such change occurred. Unless we may make 

 the hnprobable assumption of a simultaneous reversal in the sign of 

 the charge at high levels and the sign of the charge or the direction 

 of whirl in the deep-seated spot vortex, the electromagnetic theory 

 must be abandoned. 



From the hydrodynamic standpoint, we may assume the effect of 

 the spot on the higher atmosphere to be a direct downward suction, the 

 direction of the whirl at the two levels being detennined by the con- 

 ditions existing in the upper and lower regions. Final conclusions, 

 however, must await the arrival of the sun-spot maximum and the 

 completion of a series of vortex experiments, which tend to strengthen 

 the hydrodynamic view. 



The parallel investigation on the general magnetic field of the sun 

 has confimied the conclusion, mentioned in the last annual report, 

 that the magnetic axis does not exactly comcide with the axis of 

 rotation (p. 240). Though the inchnation of the magnetic axis is 

 considerably smaller than in the case of the earth, the analogy between 

 the solar and terrestrial fields, which also agree in polarity, is decidedly 

 strengthened by the fact that in both cases the two axes fail to coincide. 



