l66 REPORTS 0? INVESTIGATIONS AND PROJECTS. 



quadruplets when observed across the Hnes of force. With the dispersion 

 available, such lines can not be resolved into quadruplets in the spot- 

 spectrum. 



(14) Spot triplets are found in the laboratory to be triplets when observed 

 across the lines of force. 



(15) Certain triplets and quadruplets of iron show nearly the same rela- 

 tive separation of their components in spot and laboratory. 



(16) From the measurement of such lines, the maximum strength of the 

 field is found to range from about 2,900 to about 4,500 c. g. s. units in differ- 

 ent spots. 



(17) The strength of the field is generally greatest near the center of the 

 umbra and decreases gradually in intensity across the penumbra. 



(18) An appreciable field is shown by certain lines to extend beyond the 

 boundaries of the penumbra. 



(19) Magnetic fields have also been found on the solar disk entirely out- 

 side of sun-spots. 



(20) The doublets and triplets of iron give the strongest fields hitherto 

 measured in sun-spots. The D lines of sodium and the b lines of magnesium, 

 which are produced at a higher level in the solar atmosphere, usually indicate 

 a much weaker field. The hydrogen lines over sun-spots, representing a still 

 higher level, give no indication of a magnetic field. It therefore follows that 

 the strength of the field in sun-spots rapidly decreases in passing upward 

 from the surface of the photosphere. 



(21) Preston's law, —^ = const., is approximately followed by iron 



A 



doublets observed in the laboratory (using mean values of AX) and less 

 accurately so by spot doublets. 



(22) The degree of widening of unresolved lines in the spot-spectrum 

 decreases rapidly from the red to the violet, and is roughly proportional to 

 the separation of their components in the laboratory. 



(23) A direct relationship appears to exist between the strengthening and 

 the widening of lines in spot-spectra. 



(24) As the strength of the field is greatest at low levels, it appears 

 probable that the electric vortex which produces the field lies within the 

 photosphere. 



(25) The strength of the field in sun-spots is not sufficient to account for 

 magnetic storms on the earth. 



I am continuing the investigation with the 60-foot tower telescope on 

 Mount Wilson, and Dr. King, who has done all of the laboratory work, is 

 making an extensive study of the Zeeman effect in Pasadena. As soon as the 

 1 50- foot tower telescope and the 75-foot spectrograph are completed, it 

 should be possible to obtain many new results. 



Mr. Adams, aided by members of the computing division, has completed a 

 .catalogue of about 14,000 lines in the spectra of sun-spots. Dr. King has 



