142 REPORTS OF INVESTIGATIONS AND PROJECTS. 



(3) Winged lines change greatly in appearance, the wings being much 



reduced near the limb. 



(4) Most of the lines in the spectrum are slightly widened near the 



limb. 



(5) The ultra-violet cyanogen fluting is decidedly decreased in inten- 



sity, while the blue carbon fluting is not affected in the same 

 degree. 



(6) Most of the metallic lines are shifted toward the red, with respect 



to their position at the center of the sun. 



(7) The shift is not due to ascending currents at the center of the sun, 



as is shown by measures upon plates taken with the arc spectrum 

 for comparison. 



(8) The amount of the shift varies for different lines of the same ele- 



ment. 



(9) The cyanogen fluting is not shifted from its normal position. 



Other changes might be mentioned, but these are among the most charac- 

 teristic. It now seems probable that the phenomena can not be attributed to 

 any single cause, and that considerable work will be required to arrive at a 

 plausible explanation of the results. As mentioned elsewhere in this report, 

 a series of laboratory investigations will soon be undertaken on a list of lines 

 whose behavior is being studied in sun-spots and near the sun's limb. 



Spectro graphic Investigations of the Solar Rotation. — Mr. Adams's photo- 

 graphic investigation of the rotation of the sun by the spectroscopic method 

 has been continued during the year, and the results obtained are now being 

 put into definitive form for publication. The region of the spectrum selected 

 for this work lies in the violet, with its center near X 4250, and all of the 

 photographs have been taken in the fourth order of the 18-foot Littrow 

 spectrograph. A total of 41 plates has been measured, each containing 6 

 exposures, which correspond to separate latitudes upon the sun's surface. 

 The larger part of the work of measurement has been done by Miss Lasby 

 of the computing division. Since 20 lines have been measured upon each 

 exposure, the labor has necessarily been great. A short summary of the 

 results is given below. Both the velocities and the daily angular motions are 

 reduced to the sidereal period. 



