THE SUN. 75 



covery of black spots on its surface, which, when watched 

 from day to day, were found to change their situation on 

 its disc, in a certain regular manner ; coming in, or 

 making their first appearance on the eastern edge or 

 border of the disc: i.e.^ on the left-hand side of the sun 

 when seen at noonday ; and going off, or disappearing 

 at the west, or on the right-hand side. It very soon 

 became evident that, whatever these spots might be, they 

 adhered to the body of the sun, and that their apparent 

 motions could only be accounted for by a real motion ot 

 rotation of the sun on an axis nearly, but not quite, per- 

 pendicular to the ecliptic. By foJlowing out this indica- 

 tion by careful observation and calculation, it has become 

 known that the sun does so rotate; that the time 

 occupied in a single rotation is very nearly 25 days 7 

 hours 48 minutes ; that the axis of rotation is about 7 

 inclined to a line perpendicular to the ecliptic, its direc- 

 tion in space being that of a line pointing nearly to the 

 star r (tau), in the constellation of the Dragon ; in con- 

 sequence of which on and about the nth of June, the 

 spots appear to pass across the sun in straight lines, from 

 the apparent northern to the apparent southern hemi- 

 sphere of the sun, and the reverse on and about the 12th 

 of December, while at intervening times, their course 

 across the sun is a flattened elliptical or oval curve ; a 

 necessary consequence of their real motion being in a 

 circle much inclined to the line of sight. Their ellipses 

 are most open on the nth of March, and the 13th of Sep- 

 tember; on the former of whicli days we get the best view of 

 the south pole of the sun, and on the latter of the north. 



