1903.] Solar Prominence and Spot Circulation, 1872—1901. 447 



corroborated Carrington's results and extended the discussion of the 

 observations up to the end of the year 1879. 



The result of these two investigations showed that at sunspot 

 maximum there was only one zone in each hemisphere in which spots 

 were situated, the centre of this being about 18° N and S, while at 

 minimum there were two zones existing simultaneously in each hemi- 

 sphere ; the older cycle dying out in the zone, the centre of which, was 

 situated in low latitudes, and the new one commencing in high latitudes, 

 its centre being about latitude ± 30° to ± 35°. 



Later observations extending up the present year have further cor- 

 roborated these general deductions, for each hemisphere, and we are 

 now quite familiar with this cycle of sunspot latitude variation. 



In the present investigation, the fact has been brought out that the 

 prominences also undergo an apparently regular variation of latitude 

 throughout a period of about eleven years concurrently with the 

 spots. 



For the purpose of our inquiry, the object of which has been stated 

 above, we have discussed independently of each other, two fine 

 series of prominence observations, one made by Tacchini at Rome 

 extending from 1872 to 1900, and the other by Ricco and Mascari at 

 Catania from 1881 to 1901. 



Both these series were handled in the same way, and both indicated 

 similar changes of latitude of prominence action, showing that the 

 variations recorded were real and not due to any personality of the 

 observer or difference in the method of observation. 



The data for the discussion of the solar prominences as observed by 

 Tacchini have been taken from the same source as before,* while those 

 of Ricco and Mascari are published in and have been extracted from 

 the same volumes. 



We may here take the opportunity to express our thanks to 

 Professor Ricco, with whom we have been in communication, and who 

 has very kindly forwarded for our use some unpublished data con- 

 cerning his prominence observations and reductions. 



The method of reduction adopted was to determine for each year 

 the percentage frequency of prominence activity for every 10 degrees 

 of solar latitude north and south, A series of curves was next 

 drawn, one for each year, the abscissas representing the latitudes of 

 prominences north and south, and the ordinates their percentage 

 frequency. It was then found that the centres of prominence 

 activity, or, in other words, the maxima of the curves, were sometimes 

 single, sometimes double, and in one or two cases even triple in each 

 hemisphere. This suggested that just as sometimes there are two 



1874 — Dec, 1879.' ' Publicationen des Astropbysikalischen Observatoriums zu 

 Potsdam,' Band I and II. 



* ' Societa Spettroscopisti Italiani,' vol. 1, 1872, to vol. 29, 1900. 



2 K 2 



