SOLAR OBSERVATORY * 



George E. Hale, Director. 



The principal results accomplished during the past year may be sum- 

 marized as follows: 



(i) The probable existence of magnetic fields in sun-spots, mentioned in 

 my last report, has been placed beyond doubt through the detection of all 

 the characteristic phenomena of the Zeeman effect. 



(2) As the only known way in which such magnetic fields could be pro- 

 duced at the temperature of the sun is by the rapid revolution of electrically 

 charged particles, it thus appears probable that sun-spots are electric vortices. 



(3) Photographs made with the spectroheliograph and the circular polari- 

 zation phenomena of the double lines in spot spectra agree in indicating that 

 the sun-spot vortices generally rotate in opposite directions in the northern 

 and southern hemispheres. This statement applies particularly to the larger 

 spots, but some large spots, as well as many smaller ones, do not conform to 

 this rule. 



(4) The areas of the calcium flocculi, as measured on the spectrohelio- 

 graph plates, give a new index to the solar activity. A curve showing the 

 mean area corresponding to each solar rotation period, when compared by 

 Dr. Bauer with a curve exhibiting the variations in the earth's magnetic 

 intensity, indicates a general relationship between the solar activity and the 

 terrestrial magnetic activity. No quantitative relationship for individual 

 cases can, however, be detected. 



(5) Comparative studies of the hydrogen flocculi, made with moderate 

 and high dispersion, have shown their changes in intensity and form in the 

 vortices, their structure as photographed with different lines and with differ- 

 ent parts of the same line, and their characteristic phenomena at different 

 levels in the solar atmosphere. 



(6) The radial motion of the calcium vapor in the Hg and H3 flocculi has 

 been measured in many parts of the sun's disk. 



(7) The "flash" spectrum of the lower chromosphere, previously photo- 

 graphed only at total eclipses of the sun, can be photographed in full sun- 

 light on any good day with the 30-foot spectroheliograph of the tower 

 telescope. The wave-lengths of the bright lines thus recorded are, on the 

 average, in close agreement with those of the corresponding dark lines in 

 Rowland's table. 



*Situated on Mount Wilson, California. Grant No. 543. $104,000 for construction, 

 investigations, and maintenance. (For previous reports see Year Books Nos. 3, 4, 5, 6, 

 and 7.) 



II — YB 159 



