atmosphere, where the hydrogen flocculi float, the 

 period of rotation for any latitude is less than for 

 the levels below, but the difference in rotation 

 time between pole and equator is less marked than 

 in the lower atmosphere. 



a 



FIG. 15. a, Direct photograph of Sun, August 31. 1906; b. Calcium 

 (Hz) Flocculi at same hour. 



SOLAR AND STELLAR SPECTROSCOPY. 



Since the flocculi are constantly changing in 

 form, they are not very satisfactory objects for 

 rotation measurements. Much more accurate 

 results can be obtained by measuring, with a 

 powerful spectrograph, the velocity of approach 

 and recession of the east and west edges of the sun. 

 The east edge is moving toward the earth on 

 account of the sun's rotation; this causes a dis- 

 placement of the spectrum lines toward the violet 

 (Fig. 1 6). At the west edge, which is moving away, 

 the lines are equally displaced toward the red. The 

 double displacement, measured at different lati- 



