SOLAE VOETICES AND MAGNETISM IN SUN SPOTS ABBOT. 323 



graphed in hydrogeii, calcium, or iron light, and in the case of hydro- 

 gen, which has lines in several parts of the spectrum, the light may 

 be either violet, blue, or red. Spectroheliogi'aphic pictures show 

 many details not seen in telescopic views of the sun. Mr. Hale has 

 named the elementary patches which go to make up this newly found 

 detail " flocculi." Recently very striking and interesting photo- 

 graphs of solar structure have been made by the spectroheliograph 

 at the IMount Wilson Solar Observatory under Mr. Hale's direction, 

 and the following abstract of an account of some of them is taken 

 from his paper entitled " Solar Vortices : " * 



SOLAR VORTICES. 



The problem of interpreting the complex solar phenomena recorded by the 

 spectroheliograph has occupied my attention since the first work with this 

 instrument in 1892. The measurement of the daily motions in longitude of the 

 calcium flocculi has led to several new determinations of the solar rotation,'' 

 and their areas, measured by a photometric method, are being used as an 

 index to the solar activity. Various investigations on their forms at different 

 levels,*' their distribution in latitude and longitude, etc., have also been carried 

 out. But the failure of the calcium flocculi to indicate the existence of definite 

 currents in the solar atmosphere has been a disappointment. 



The hydrogen flocculi, though occupying the same general regions on the sun's 

 disk, are distinguished from those of calcium by several striking peculiarities. 

 In the flrst place, most of them are dark, while the corresponding calcium (Hs) 

 flocculi are bright. Secondly, as I have recently shown,'^ they seem to obey a 

 different law of rotation, in which the equatorial acceleration (better, the polar 

 retardation), shared by the spots, faculje, and calcium flocculi, does not appeal*. 

 A third peculiarity, briefly mentioned in previous papers, is clearly visible on 

 many hydrogen photographs. It is a decided deflniteness of structure, indicated 

 by radial or curving lines, or by some such distribution of the minor flocculi 

 as iron filings present in a magnetic field (see, for example, Astrophysical 

 Journal, Vol. XIX. ris. X and XII). First recognizetl at the beginning of 

 our work with the hydrogen lines in 1903, this suggestive structure has re- 

 peatedly shown itself on the Mount Wilson negatives. But its true meaning 

 did not appear until the results described in this paper had been obtained. 



With the Rumford spectroheliograph the hydrogen lines H/3, H7, and 115 

 were used. Certain differences between the photogi-aphs, which seemed to 

 depend upon the wave length, pointed to the desirability of trying Ha, but 

 plates sufficiently sensitive to red light were not to be had at that time, and 

 therefore the experiment was postponed. 



The extreme sensitiveness in the red of plates prepared according to a formula 

 due to Wallace " now renders it a simple matter to photograph the sun with Ha. 



"Astrophysical Journal, Vol. XXVIII (September), 1908. [The plate num- 

 bers do not correspond with those in original paper. — Editor.] 



*Hale and Fox, The Rotation of the Sun, as Determined from the Motions 

 of the Calcium Flocculi. Carnegie Institution (in press) ; Fox, Science. April 

 19, 1907; Hale, Contributions from the Mount Wilson Solar Observatory, No. 25; 

 Astrophysical Journal, Vol. XXVII, p. 219, 1908. 



^Hale and Ellermau, Publications of the Yerkes Observatory, Vol. Ill, pt. I. 



"^Hale, Contributions from the Mount Wilson Solar Observatory, No. 25; 

 Astrophysical Journal, Vol. XXVII, p. 219, 1908. 



« Astrophysical Journal, Vol. XXVI, p. 299, 1907. 



