450 Sir Norman Lockyer and Dr. W. J. S. Lockyer. [Mar. 17, 



occurs in a zone nearer the equator (latitude ± 24°), which also 

 increases rapidly in intensity. 



After these general statements, we now refer to some details 

 showing that there are some variations from the above generalisa- 

 tion. 



For these details the curves deduced from both sets of observations 

 made by the different observers are so very similar that it does not 

 matter which are examined. 



Attention may first be drawn to certain differences between the 

 curves representing the latitude variation for the two hemispheres. 

 It will be noticed that for the period 1872 — 1882, the curves for both 

 hemispheres are very similar. We next consider the period 1880 — ■ 

 1893. Here there are differences between the two hemispheres. The 

 curve for the northern hemisphere resembles very closely that for the 

 preceding period, but it differs somewhat from its corresponding curve 

 for the southern hemisphere. The corresponding northern zone in 

 latitude 45° is missing from the southern hemisphere, while a zone of 

 activity nearer the equator about latitude 24° is present. Further, 

 the polar zone for the southern hemisphere continues to be prominent 

 for two years longer than that in the opposite hemisphere. 



In the succeeding curves, which extend from 1891 — 1901, both 

 hemispheres are more or less similar, and both resemble in a greater 

 degree those for the southern hemisphere for the period 1880 — 1893 

 than those for the period 1872—1882. 



Although the Eoman and Sicilian observations give nearly identical 

 curves, hemisphere for hemisphere, the apparently regular cycle of 

 change of latitude which was operative for the northern hemisphere 

 1872 — 1893, and for the southern hemisphere 1872 — 1882, does not 

 seem to have been so exactly maintained in late years ; more irregular 

 still perhaps is the last cycle commencing in the year 1892. Hence, 

 there seems reason to believe that the j)rominence circulation is not 

 quite the same for each cycle, and this may in some way be due to a 

 longer solar period such as that of about 35 years. 



But it is important to state that our deductions may be partially 

 incomplete owing to the difficulty of determining sometimes whether a 

 new centre of action has been formed or the position of an old one 

 changed. Further, account must be taken of the fact that the material 

 discussed does not represent the record of the percentage frequency of 

 prominences determined from observations made on the disc of the 

 sun (now rendered possible by the Janssen-Hale-Deslandres method), 

 but one obtained from observations of the phenomena occurring only 

 at the limb of the sun. The close agreement between the observation 

 of the different observers shows nevertheless that this latter method is 

 of great value. 



Another important series of prominence observations is that made 



