1914.] HALE— SOLAR MAGNETIC PHENOMENA. 255 



Zaeman effect, indicate that the well-known widening and displace- 

 ment of the solar lines near the limb are not due primarily to this 

 cause, though there may prove to be a second order effect smaller 

 than I have yet been able to recognize. 



A compound half-wave plate, made of narrow strips of half- 

 wave mica, so mounted that (when used w-ith a Xicol) the alternate 

 strips will transmit light polarized in planes at right angles to one 

 another, is to be strongly recommended for this purpose. This will 

 permit the widths and the positions of the solar lines to be compared 

 on a single photograph, in the way which has proved so advantageous 

 in the study of the sun's general magnetic field. ^ 



In a preliminary study of our photographs of sun-spot spectra, 

 some of which were taken with the Nicol alone, I have been unable to 

 detect any promising evidence of the Stark effect- However, these 

 plates are poorly adapted for the purpose, and the investigation will 

 soon be continued, and extended to various parts of the solar 

 atmosphere. 



2 Contributions from the Mount Wilson Solar Observatory, No. 71. 



