xxviii.] SUCCESSION OF SPOTS. 431 



Nothing could more closely indicate than these curves 

 the fact that in both hemispheres, north and south alike, the 

 spots are formed successively in lower latitudes, one cycle 

 beginning before the former one is ended. 



Hence we are driven by the hypothesis to assume an upper 

 outward current from the poles. Here we find ourselves in 

 a part of solar physics where the facts are almost entirely 

 wanting. 



With regard to these currents it must at once be pointed out 

 that as the falls occur in different longitudes the strengths of 

 the currents will not be the same in all longitudes. And if the 

 currents are more intense in one longitude, and if they really 

 do bring with them the spot-forming materials, we should 

 expect spots, when there are fewest of them (when we can 

 best study their action) to have a tendency to form along 

 meridians. A discussion of the spots observed in the years 

 1878 and 1879 certainly shows that there was such a tendency 

 very strongly marked. 



Nor is this all. An action once set up along a meridian may 

 be the cause of a succession of spots breaking out in the same 

 longitude, even after some considerable interval of time. On this 

 I quote the following from Carrington : l 



" 667. A group seen twice, on March 13th and 15th. Not seen 

 on the 18th. In the next rotation 690 occupies the same position, 

 and in the third rotation a large group (771) succeeds. There is no 

 question that the three are successive independent formations or 

 outbreaks in the same region. This and other cases (668 im- 

 mediately before is another) indicate that the source of energy 

 which leads to the formation of a spot or group is not always 

 exhausted on the disappearance of the group ; that corresponding to 

 the visible spot there is an invisible overhanging cloud or under- 

 lying volcano, the discharge of which rupturing or displacing the 

 photosphere is sometimes intermittent." 



1 Carrington, Observations of Solar Spots, p. 176. 



