KO. 1865 



OUR KNOWLEDGE OE THE SUN — HALE 



355 



The following table brings together the results of various deter- 

 minations of the solar rotation : 



The long series of observations by Carrington, Spoerer, and 

 Maunder furnish ample material for the study of Sun-spot motions, 

 but it is doubtful whether such results should be combined, since 

 they cover long time intervals, during which (as some evidence sug- 

 gests) the rotation period may undergo variation. The same may 

 he said of the flocculi. The unweighted means of determinations of 

 the motions of the calcium flocculi, made at the Kenwood, Yerkes 

 and Mount Wilson Observatories, differ so little from the mean 

 motions of the spots that no safe conclusions can be drawn. Strato- 

 noff's results for the faculje are of rather low weight, since they com- 

 prise a comparatively small number of measures, necessarily made 

 near the Sun's limb (since the faculce are not visible near the center 

 of the disk), and therefore subject to greater errors of setting. 



But if we are not warranted in concluding that the calcium flocculi 

 move more rapidly than the spots, we may at least recognize the 

 striking differences which distinguish their rotational motions from 

 those of the hydrogen flocculi. The lower calcium clouds follow the 

 motions of the spots, and show the same marked acceleration of 

 angular velocity toward the equator. The hydrogen flocculi, floating 



