1903.] Solar Prominences and Terrestrial Magnetism,. 245 



In the curves accompanying the present communication (Plate 4) 

 the above-mentioned set, except those for 80° — 90° north and south, 

 have been grouped in pairs, thus representing the percentage frequency 

 of prominences in each hemisphere for zones of 20° of latitude, 

 0° — 20°, 20° — 40°, &c, since it was found that this reduction could be 

 made without losing any of the characteristic variations. 



An examination of these curves shows that they differ very con- 

 siderably one from the other as Ave proceed from the equatorial to 

 the polar zones. Generally speaking the curves representing the 

 variations for each of the zones, 0° — 20° north and south, conform 

 with the sun-spot curve; that is, the maxima and minima occur at 

 about the epochs of sun-spot maxima and minima. Those for the two 

 zones, 20° — 40°, in both hemispheres conform also in the main to the 

 general sun-spot curve, but in addition they display subsidiary 

 maxima or changes of curvature superimposed on the main curve. 



The curves for the two zones, 40° — 60° north and south, have, on 

 the other hand, hardly any likeness to the sun-spot curve, but are 

 made up of a series of prominent maxima representing special out- 

 bursts of prominence activity. 



Passing to the curves corresponding to the next zones, i.e., 60° — 80° 

 north and south, these indicate two prominent outbursts lasting for a 

 short period, showing that this region of the sun is, as a rule, practi- 

 cally free from prominence activity ; in the remaining zones, 80° — 90° 

 north and south, the variation is small, and is a faint echo of the 

 condition of affairs in the neighbouring zone 60° — 80°. 



The Magnetic Curves. 



The data regarding the magnetic phenomena employed in this com- 

 parison are those brought together by Mr. William Ellis, in two 

 published papers on magnetic phenomena.* 



We may take the opportunity here of thanking Mr. Ellis for kindly 

 communicating to us a continuation of the data published in these two 

 papers, which information he has brought down to the year 1899. 



Two classes of magnetic phenomena were there dealt with, namely, 

 the variations from year to year of the diurnal range of the declina- 

 tion and horizontal force, and magnetic disturbances. 



As regards the former, Mr. Ellis has shownf that the curves indi- 

 cating these variations are very similar to that of the general sun-spot 

 curve; in fact, the curves were found to be almost identical in all 

 their smaller irregularities. 



* ' Phil. Trans.,' Part II, 1880, " On the Eelation between the Diurnal Eange of 

 Magnetic Decimation and Horizontal Force, as observed at the Eoyal Observatory, 

 Greenwich, during the years 1841 to 1877, and the Period of Solar Spot Fre- 

 quency"; 'Monthly Notices, E.A.S.,' December, 1899, vol. 60, Js T o. 2, " On the 

 Eelation between Magnetic Disturbance and the Period of Solar Spot Frequency." 



f ' Phil. Trans.,' Part II, 1880. 



