l68 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Spectra of Sun-spots. 



The study of the spectra of sun-spots is being continued regularly in so far 

 as the low condition of the solar activity permits. This includes the deter- 

 mination of the polarity and strength of magnetic field of each spot, and of 

 the penumbra surrounding it, and an investigation, by the aid of the spectro- 

 heliograph, of the configuration of the Ha flocculi in its vicinity. 



An extended investigation of the motion and condition of calcium vapor 

 over sun-spots and neighboring regions has been made by Mr. St. John dur- 

 ing the past year and is being continued with the aid of the Snow and tower 

 telescopes. In addition to the calcium lines, the D lines of sodium, the h lines 

 of magnesium, and Ha will be included in the further study of this important 

 question of the circulation of the gases in the vicinity of sun-spots. The 

 results for calcium have shown that : 



(i) In most sun-spots the calcium vapor is descending over the umbrae 

 with velocities ranging from 0.7 km. to 2.2 km. per second for different spots. 



(2) Over the penumbras the vapor giving rise to bright Kg has little if any 

 vertical motion, while the vapor producing the absorption K3 is descending 

 with about the same mean velocity as over the general solar surface. 



(3) This descending motion is true as well of the absorbing vapor over 

 the flocculi and the regions immediately outside of the flocculi, while the 

 emitting vapor over the flocculi shows a possible slight motion of ascent. 



(4) A radial motion inward across the penumbrse is shown both by the 

 emitting and the absorbing vapor, the latter moving with the greater velocity. 



(5) Occasionally rotary motion around the umbrae of sun-spots is shown 

 both by the emitting and the absorbing vapor. When this occurs the combi- 

 nation of the radial and the rotary motions results in a vertical motion 

 directed toward the umbra, but the direction of rotation does not appear to 

 depend upon the position of the spot in reference to the sun's equator. 



In addition to this investigation of the motion of calcium vapor in and 

 around sun-spots, Mr. St. John is engaged upon a study of the radial motions 

 of the vapors in spots, an effect first discovered by Evershed. The following 

 results are shown by the photographs already obtained : 



(i) All of the vapors of the reversing layer and chromosphere are con- 

 cerned in the movements. 



(2) Of the high chromospheric vapors, viz, calcium, hydrogen, magne- 

 sium, and sodium, the calcium always, the hydrogen generally, and the 

 magnesium and sodium frequently are flowing into the spots, as shown by 

 the displacements of the strongest and probably high-level lines of these 

 elements. 



(3) The displacements of the other lines of calcium, magnesium, and 

 sodium, and of the lines of the reversing layer, are in the opposite direction 

 and indicate an outflow of the lower-lying vapors, the highest velocity of 

 outflow being associated with the lowest levels, on the assumption that the 

 weaker lines are produced at the lower levels. 



