H. Grew — Rotation of the Sun. 



159 



these different absorbing loci may differ in their distance from the 

 center of the sun, the velocity of each portion of the section, 

 resolved in the line of sight, will be the same. 



It will not be surprising, therefore, if in the following table 

 no connection is seen between the order of the velocities and 

 the order in which the elements are generally supposed to be 

 distributed* in the solar atmosphere. 



Table II. 



Line. 



No. obs. 



Substance. 



v'-v" 



E 3 



26 



Fe 



2-289 



"1474" 



• 74 



Helium + Fe 



2-291 



E x (double) 



36 



Fe + Ca 



2-302 



Do 



50 



Na 



2-320 



D, 



106 



Na 



2-420 



5173-838 



55 



Ti(?)f 



2-590 



5171-714 



21 



Fe 



2-608 



5166-3 



8 



Fet 



2670 



As a further possible test, I selected the " 1474 " line, of 

 which the upper component is helium, and the lower, iron. It, 

 if any, might be supposed to vary in width in passing from the 

 eastern to the western limb of the sun. Accordingly one limb 

 was. brought upon the slit, and the micrometer run from one 

 component to the other ; the image was next shifted so that the 

 other limb could be observed and the width again measured. 

 The result, however, was entirely negative ; not the slightest 

 difference could be found. With this instrument a displace- 

 ment as great as g-^- of the distance between T) 1 and D 2 would 

 have been detected with certainty. Hence we conclude that, 

 if the locus of absorption for helium is different from that for 

 iron, and if the one be drifting with reference to the other, the 

 rate of this motion is less than one-third of a mile per second. 



All attempts to measure the displacement of the helium line, 

 D 3 resulted in failure, the line as seen in the fourth order not 

 having sufficient sharpness to admit of any accuracy whatever. 



In the absence of other evidence, the fair inference from 

 these observations appears, therefore, to be that there is a lag- 

 ging of the locus of absorption in the equatorial regions, and 

 that the amount of this drift is approximately expressed by the 

 following equation for the daily angular motion of any point 

 whose heliocentric latitude is £, expressed in degrees. 



0=794' (1+0-00335J ). 



* For this distribution, see Lockyer's Chemistry of the Sun, pp. 161-169. 



f Schellen's Spectrum Analysis, p. 598. % Chemistry of Sun, p. 320. 



