1903.] Solar Prominence and Spot Circulation, 1872—1901. 449 



subsidiary maxima for the whole period covered by the observations, 

 the results illustrated graphically in Plates 6 and 7 were obtained. 



In these figures the facts are brought together for each hemisphere 

 separately. The niedials of the lines (curves A and B) show the 

 heliographic latitudes of the centres of prominence action ; the thick- 

 ness of these lines represents the relative percentage frequency of 

 prominence action. 



For the sake of comparison, three other curves for each hemisphere 

 are given. The first (curve C) shows the mean heliographic latitude 

 of spotted area for each hemisphere. For the construction of these, 

 the values, since 1873, have been extracted from the Greenwich 

 Reductions,* but previous to that date the values have been obtained 

 from Mr. Marth's reductions,! and those completed at the Solar 

 Physics Observatory from measures supplied by Professor Backlund, 

 of the Wilna Observatory. 



The next curve (curve D) illustrates the variations of the per- 

 centage frequency of prominence action for each hemisphere taken, as 

 a whole, and is similar to those given in our former papers. 



The last curve (curve E) shows the variation of the mean daily 

 area of sunspots from year to year, also for each hemisphere. 



Referring now to the changes of latitude of the prominence centres 

 of activity, both series of curves for the north as well as for the south 

 hemisphere exhibit the same general features. 



The first conclusion illustrated by the curves is that prominence 

 activity in the main has a poleward drift, that is, the change of 

 position of the zones of activity is in the direction from low to high 

 latitudes. In some years, the centres of activity appear to form two 

 zones in each hemisphere at about latitudes ± 24° and ± 50°, which 

 eventually amalgamate at about latitude ± 40° and move polewards, 

 fading out in about ± 70° to ± 80°. As this zone disappears in high 

 latitudes a new zone at about latitude ±20° begins, and this after a 

 few years becomes associated with another zone in about latitude 

 ±50°, and eventually amalgamates with it. 



The epochs at which these different zones come into play in relation 

 to the general curve of prominence activity for the whole hemisphere 

 are as follows : From a little after the maximum of prominence 

 activity to just before the minimum, two zones in the latitudes ± 24° 

 and ± 50° are in existence and of decreasing intensity. Before the 

 minimum is reached these two zones amalgamate in about latitude ± 40°. 

 At the minimum there is only one zone, and this of small intensity. 

 Between the minimum and the following maximum this zone rapidly 

 takes a northern movement, increasing in intensity ; a new outburst 



* 1 Spectroscopic and Photographic Observations made at Royal Observatory, 

 Greenwich, 1884,' and after, 

 f MSS. at Royal Society. 



