FIG. 1. PLANETS COMPAKED WITH A QUAETEB, OF THE SUN. 



which appear to traverse from west to east, across its face ; 

 these however do not travel on, but are carried round by 

 the sun in its rotation, for by observing any one of them, it 

 is seen to go across and make its appearance again at the 

 other side, and the time it takes to arrive at the place where 

 it was first seen, determines the time of the sun's rotation, 

 which (as before stated) is twenty-five days or nearly ; these 

 spots alter in size, form, and number from time to time, 

 some of them remaining permanent for months, others 

 closing in and disappearing in a few hours. 



These black spots have a sort of shadowy fringe (penumbra) 

 which gives them the appearance of being openings through 

 a luminous surface, discovering a surface less luminous, with 

 openings in it through which some still darker surface is 

 seen ; that this really is the case, and that these are not 



