XXVIII.] 



CARRINGTON'S WORK. 



425 



the spots appear to cross the sun is about twenty-eight days. 

 This is what is termed the synodic period, because the observa- 

 tions are made from the earth, which is moving in the same 

 direction as the spots while the observations are being made. 

 Making the correction for the movement of the earth, and 



FIG. 125. Curve showing the period of rotation of the photosphere in different 

 latitudes north and south, from Carrington's observations ; 851' of solar 

 longitude per diem = rate of rotation in lat. 15 N. The vertical lines 

 represent differences of 10' of longitude, + to the right, - to the left, of 

 the line cutting the curve in lat. 15 N. 



getting the actual period, the twenty-eight days have to be 

 brought down to something like twenty-six for an average spot. 

 Carrington paid very great attention to this point, and to 



