46 A CENTURY'S PROGRESS IN ASTRONOMY. 



acceleration. From observations at his little 

 private observatory at Anclam in Pomerania, 

 continued at the Astrophysical Observatory in 

 Potsdam, Sporer demonstrated a remarkable law 

 regarding sun-spots. This law is thus described 

 by a well-known astronomer : " The disturbance 

 which produces the spots of a given sun-spot 

 period first manifests itself in two belts about 

 thirty degrees north and south of the Sun's 

 equator. These belts then draw in toward the 

 equator, and the sun-spot maximum occurs when 

 their latitude is about sixteen degrees ; while 

 the disturbance gradually and finally dies out 

 at a latitude of eight or ten degrees. Two or 

 three years before this disappearance, however, 

 two new zones of disturbance show themselves. 

 Thus, at the sun-spot minimum there are four 

 well-marked spot-belts, two near the equator, 

 due to the expiring disturbance, and two in 

 high latitudes, due to the newly beginning 

 outbreak." These remarkable discoveries, which 

 resulted from the investigations of Schwabe, 

 Carrington, and Sporer, are a brilliant example 

 of what may be done by amateurs in astronomy. 

 At the time when Carrington and Sporer were 

 pursuing these researches, the spectroscope came 

 into use as an astronomical instrument, and since 

 1859 solar astronomy has been almost entirely 



