SOLAR obse;rvatory. 165 



the results prove conclusively that great electric and magnetic phenomena 

 play an important part in the sun. The results of the observations thus far 

 completed may be summarized as follows : 



(i) In the spectra of sun-spots most of the Fraunhofer lines are widened, 

 some are changed to doublets (incompletely resolved quadruplets), and some 

 to triplets. Others probably have a still more complex structure. 



(2) The component lines of spot doublets are circularly (or elliptically) 

 polarized in opposite directions (longitudinal effect in a magnetic field.) 



(3) Many lines not resolved in the spot spectrum are displaced when the 

 nicol (used with a Fresnel rhomb before the spectrograph slit) is rotated. 



(4) When the nicol, used with rhomb, is set at a certain angle, it trans- 

 mits the red components of doublets in the spectrum of a right-handed vortex 

 and the violet components in a left-handed vortex. 



(5) Although the larger spots in the northern and southern hemispheres 

 of the sun are usually found to be of opposite polarity, it frequently happens 

 that spots of opposite polarity occur in the same hemisphere, often in the 

 same spot-group. 



(6) Triplets have been found in all our best photographs of spot-spectra, 

 including those taken when the spot was near the center of the sun. 



(7) The central component of such triplets is plane polarized, while the 

 outer components are elliptically polarized. 



(8) Many lines which are widened but not resolved in spot-spectra can be 

 shown to be triplets by cutting out the central component with a nicol placed 

 at a suitable angle. 



(9) Under certain conditions, when a nicol is used, the central line of a 

 spot triplet is present on one side of the spot and absent on the other. Rota- 

 tion of the nicol through 90° reverses the appearance, causing the line to 

 appear on the side where it was previously absent and to disappear on the 

 opposite side. This effect is provisionally attributed to a rotation of the 

 plane of polarization of the plane polarized light emitted by the central line, 

 when passing outward through the spot-vapors. 



(10) The width of the components of a spot triplet sometimes varies with 

 the position of the nicol. This may be the result of the combined effect of 

 the rotation of the plane of polarization and the rapid decrease upward in 

 the strength of the field above the spot. 



(11) The intensity of the central line of a spot triplet varies with the posi- 

 tion of the spot on the sun's surface, and is greatest near the limb. 



(12) The intensity of the central line of a triplet in a spot near the center 

 of the sun is such as to indicate that the lines of force of the magnetic field 

 usually make a considerable angle with the solar radius passing through the 

 spot. 



(13) Lines which appear as doublets in the spot-spectrum are found in 

 the laboratory to be doublets when observed along the lines of force, and 



