\ 



February 19, 1903] 



NA TURE 



377 



C370 



750 

 CO* -30- 5oo 

 NLM I.. 



fj LAT 



M LAT 



SOLAR PROMINENCES AND TERRESTRIAL 



MAGNETISM. 



SINCE the year 1871 the Italian astronomer, Prof. 

 Tacchini, has been daily making spectroscopic observ- 

 ations of the sun, noting the number, size and position of 

 the prominences visible on the solar limb. A preliminary 

 study of this very valuable homogeneous series of 

 data rendered it possible to demonstrate that the 

 variation of the frequency of occurrence of these phenomena 

 followed a very general law, the number waxing and waning 

 at intervals of about eleven years, and synchronising with 

 •the variation of the number of spots on the sun's disc. This 

 result was pointed out some time ago in 

 the pages 01 this Journal (vol. lxvi. p. 248), 

 and it was there further stated that there 

 were in addition subsidiary maxima and 

 minima superimposed on the main eleven- 

 year curve. 



This preliminary study dealt with the 

 prominences visible on the sun's limD in 

 toto, and did not consider their frequency 

 in any particular part of it. 



A subsequent analysis indicated, however, 

 that by taking the solar limb to pieces, so 

 to speak, and dealing with the individual 

 parts of it, very interesting results might 

 accrue. This work has recently been com- 

 pleted, and it was found that the frequency 

 of prominences varied according to the par- 

 ticular solar latitude examined, and that 

 ■the phenomena of terrestrial magnetism 

 were very closely connected with these vari- 

 ations. 



In a recent communication to the Royal 

 Society 1 the comparison of these two classes 

 -of phenomena, as mentioned above, has 

 been made in some detail, and the present 

 article gives a brief account of the con- 

 clusions derived from the inquiry. 



For the reduction of the prominence ob- 

 servations the limb of the sun was divided 

 into parts ten degrees in length, corre- 

 sponding with ten-degree zones of solar 

 latitude north and south, and each zone 

 was examined and discussed by itself. 

 Further, the observations for every three 

 months were, in the first instance, grouped 

 -together, and the percentage frequency for 

 each of these periods was determined in- 

 dividually. 



In this way a set of eighteen curves, nine 

 for each hemisphere, was made, showing 

 the variation from year to year of the per- 

 centage frequency of prominence activity 

 in each ten-degree zone. 



In the curves accompanying the present 

 article (Fig. 1) the above-mentioned set, 

 except those for 8o°— 90 north and south, 

 was grouped in pairs, thus representing 

 the percentage frequency of prominences in 

 each hemisphere for zones of 20 of lati 



The curves for the two zones, 40 — 6o° 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 outbursts of prominence activity. 



Passing to the curves corresponding to the next zones, i.e. 

 60°— 8o° north and south, these indicate two prominent out- 

 bursts lasting for a short period, showing that this region 

 of the sun is, as a rule, practically free from prominence 

 activity ; in the remaining zones, 8o°— 90 north and south, 

 the variation is small, and is a faint echo of the condition of 

 affairs in the neighbouring zone 6o°— 8o°. 



The data regarding the magnetic phenomena which were 

 employed were those brought together by Mr. William 



20- -40- 



S.L.-.T 



40* - 60* 



6. L AT. 



Go'- ao- 



5. LAT 



7S1 



tude, o°— 20 c 



o°— 40 , &c, since it was 



80--30-. 

 3. LAT. 



found that this reduction could be made 

 without losing any of the characteristic 

 variations. 



An examination of these curves shows 

 that they differ very considerably one from 

 the other as we proceed from the 

 equatorial to the polar zones. Generally speaking, the 

 curves representing the variations for each,, of the zones, 

 o°— 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 zone; 

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

 the general sun-spot curve, but in addition they display sub- 

 sidiary maxima or changes of curvature superimposed on 

 the main curve. 



1 " The Relation between Solar Prominences and Terrestrial Magnetism." 

 By Sir Norman Lockyer, K.C.B., F.R.S., and William J. S. Lockyer, 

 M.A., Ph.D., F.R.A.S. (Received January 14, read January 29, 1903.) 



NO. 1738, VOL. 67] 



Fig. 1. — Curves showing the percentage frequency of solar prominences for each 20' zone 

 N. and S. (The continuous and broken vertical lines indicate the epochs of sun-spot 

 maxima and minima respectively.) 



Ellis, who very kindly brought the whole of them up to date 

 for the purposes of the present inquiry. 



Two classes of magnetic phenomena were dealt with, 

 namely, the variations from year to year of the diurnal range 

 of the declination and horizontal force, and magnetic dis- 

 turbances. As regards the former, Mr. Ellis has shown that 

 the curves indicating 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. The 

 second class of phenomena, namely, the magnetic disturb- 

 ances, which are more irregular in occurrence, has been 

 classified by Mr. Ellis into five groups, and tabulated by him 



