1825.] Rev. Mr. Emmett on the Solar Spots. 381 



Article VIII. 



On the Solar Spots. By the Rev. J. B. Emmett. 



(To the Editors of the Annals of Philosophy .) 



GENTLEMEN, Great Ouselurn, March 20, 1825. 



I SEND a few remarks and observations on the solar spots, 

 which may, perhaps, not be uninteresting to your readers. 



In common with the generahty of astronomers, I supposed the 

 solar spots, which are carried round by the rotation of the sun 

 with tolerable uniformity, to be visible and invisible for equal 

 intervals of time : being a convert to the hypothesis of the late 

 Sir W. Herschell, no doubt seemed to remain, since the equahty 

 of the periods follows of necessity. In the notes to the third 

 volume of the Jesuit's edition of Sir Isaac Newton's Principia, 

 the observations of Stannyan and Cassini are quoted, proving 

 that the time during which the spots are visible, is twelve days, 

 and that they are invisible 15 ; the learned commentators observe 

 that of all the observations which they have seen, none prove 

 that a spot has remained in view more than twelve days, or 

 returned before the 15th. Kirchius observed one from April 26 

 to July 17, 1681 ; it was twelve days visible, and fifteen invisible. 

 This observation is recorded in Chamber's Enclyclopedia, the 

 author of which work assumes this period as well known, and 

 received generally by astronomers. In the Phil. Trans. 1704, 

 the observations of Stannyan in 1703 are quoted ; a spot which 

 he observed for some days, was visible in the morning of 

 May 23 (civil time), again at, and after noon, but then upon the 

 edge of the disc ; but at o'' it had entirely vanished ; it was upon 

 the edge June 7'' S*" ; again it was on the hmb, and disappeared 

 June W 2". Now from May 23, 3'> afternoon, to June 7'*, 3" 

 afternoon, is precisely 15 days; also from June 7'*, 3'' afternoon, 

 to June l9^ 2h, is ll-* 23^ In the Phil. Trans. 1767 (when 

 telescopes had received great improvement), the Rev. S. (late 

 Bishop) Horsley, from these phenomena, calculates the altitude 

 of that part of the solar atmosphere which the spots occupy ; the 

 commentators of Newton instituted a similar problem ; Mr. 

 Horsley takes it for granted that the spots are visible for 12 

 days, and disappear during 15 ; whence it follows that the sun's 

 radius being 1, the spots are at the distance 1,013767 from his 

 center. Yet all more modern astronomers assume that the spots 

 are concealed behind the disc, and appear upon it during the 

 same interval of time. Besides the observations quoted, I 

 might have advanced many others ; yet I cannot lind any which 

 show the return of a spot before the fifteenth day, or continue it 

 on the disc more than twelve. 



Some may reply that the early observations may be erroneous 



