148 



Dr. W. J. S. Lockyer. 



[Jan. 16, 



four, distinct "spot-activity tracks," or loci of movements of the centres 

 of action of spot disturbance. 



2. The first appearance of each of these "spot-activity tracks" 

 occurs generally between a sunspot minimum and the following 

 maximum. After about the epoch of maximum generally no new 

 " spot-activity tracks " of large magnitude are commenced, 



3. Their first appearance is mostly in higher latitudes than 20° in 

 each hemisphere. 



4. They are faintly indicated at first, become more prominent and 

 distinct, and finally thin out and fade away. 



5. They all fade away in regions close to the equator. 



6. There seems to be a tendency for each successive "spot-activity 

 track" to make its appearance in latitudes higher than the one 

 preceding it. 



7. At, or a little after, the time of sunspot maximum there is 

 also a tendency for each " spot-activity track " to retain its latitude 

 for a short time. 



In the light of these curves it is interesting to analyse those formed 

 by plotting the mean yearly heliographic latitude of spotted area for 

 each hemisphere : these are given in the accompanying plates 

 (Curves B). These latter curves represent the drift from year to 

 year of the mean heliographic spot latitude, and illustrate Sporers 

 " Law of Zones." It will be noticed that each commences in high 

 latitudes about the time of sunspot minimum, and gradually approaches 

 the equator until the epoch of the following minimum, when a new 

 cycle in high latitudes recommences.* 



An important point to be noticed about this series of curves is that 

 each is of a wavy nature. This peculiarity is clearly shown even in 

 the plate illustrating Sporer's reduction f which covers the period 

 1854 — 1880. There the curves, representing the mean spotted area 

 and the mean heliographic spot latitude for both hemispheres 

 combined, were compared, and Sporer pointed out some anomalies 

 between these mean curves and those formed by joining the actual 

 points of observation. So conspicuous were these anomalies at one 

 epoch (even after many of the peculiarities had been lost by combining 

 the two hemispheres instead of treating them singly), that he drew 

 attention to them in the following words % : " Nun sieht man an den 

 Beobachtungspuncten, welche bei der Breitencurve eingetragen sind, 

 class die aus specieller Eechnung hervorgehende Curve ebenfalls eine 



* These curves should overlap, but the unit of time, namely, the year, here 

 employed, masks this feature. 



f ' Publicationen des Astrophysikalischen Observatoriums zu Potsdam,' vol. 2, 

 Erstes Stuck, No. 5, Tafel 32. 



X 1 Publicationen des Astrophysikalischen Observatoriums zu Potsdam,' vol. 2, 

 Erstes Stuck, No. 5, p. 81. 



