XXVI1I.J 



SPORER'S CURVES. 



435 



Further, we learn that another cycle really begins, as we have 

 already said, before the preceding one is finished ; so that in 

 the case of each cycle we have eight or ten years instead of 

 seven after the maximum. The sun-spot period of eleven 

 years, therefore, is the time that elapses between maximum 

 and maximum, and is shorter than each true cycle. 



The curves also show us that the maximum is reached when 

 the mean latitude of the spots is about 16 N. and S. We get 

 then a retreat from about 30 to 16=14 in four years, and the 



FIG. 130. Combination of Sporer's curves. 



further retreat from 16 to 8=8 in eight years, that is a change 

 of latitude of over 3 a year to begin with, and a change of 

 half a degree a year to end with. 



We gather then, that after latitude 16 there is a great and 

 increasing difficulty of fall. 



To discuss this properly we must now pause and take a 

 general view of the ground we have recently travelled over. 



F F 2 



