3/S 



NA TURE 



[February 19. 1903 



under five separate subheads. In this investigation only 

 that class described as " great " has been used, since this 

 group represented the largest disturbances. 



Mr. Ellis, as already has been pointed out, has indicated 

 the close resemblance between the sun-spot curve and that 

 representing the variation of the magnetic elements; and 



1870 



1880-0 



I89O-0 



IS000 



KM 



SUNSPOTS 



WAN OAILT 

 AREA 

 N HEM 



PROMINENCES 



O* - 50* 



(TACCHHl] 



MCAN WILY 

 RANGE OF r 

 MAGNETIC « 

 OECLINMION., 



l IlL ") , 



1860 



16700 



13800 



I89O0 



86OO 



670 



Fig. 2. — Comparison of curves representing variations of magnetic declination, solar 

 prominences (o a -2o° N. and S.l, and sun-spot areas. (Continuous and broken veitical 

 lines as in Fig. i.) 



it has also been shown that the curves representing the per- 

 centage frequency of prominences near the solar equator 

 conform in the main to the general sun-spot curve. 



There is, therefore, an apparent connection between 

 phenomena occurring in the equatorial regions of the sun, 

 the percentage frequency of prominences 

 near the solar equator, sun-spots (which are 

 practically restricted to these zones), and 

 the ordinary diurnal magnetic variation. 



The accompanying set of curves (Fig. 2) 

 illustrates the great similarity between 

 those showing the frequency of promin- 

 ences in a zone about the equator (o°— 20 

 north and south) and the variations of the 

 mean daily range of magnetic declination ; 

 for the sake of comparison, three other 

 curves are added, showing the variation of 

 the mean daily area of the sun-spots for 

 the whole, and the two hemispheres of the 

 sun separately. 1 



Leaving the variation of the diurnal range of the magnetic- 

 elements and turning our attention to the magnetic disturb- 

 ances, it will be seen that if a comparison of the curve repre- 

 senting the number of days of the " great " disturbances be 

 made with those representing prominence frequency (Fig. 1), 

 the former is as unlike the curves representing the promin- 

 ence frequency about the solar equator as 

 it is like those near the poles ; in fact, the 

 polar prominence outbursts and great mag- 

 netic disturbances occur almost simul- 

 taneously. 



The peculiar form and general similarity 

 of the curves can be best seen from the 

 accompanying illustration (Fig. 3). In the 

 figure comparison is made between the 

 epochs ot the crossing of the known and 

 unknown lines observed in sun-spot spectra, 

 the percentage frequency of prominences 

 about the solar poles and Ellis's " great " 

 magnetic disturbances. 



Two curves representative of promin- 

 ence frequency are given, one to indicate 

 the abrupt nature of the curves represent- 

 ing the frequency in a zone near the pole 

 10 degrees in width (in this case 6o°— 70 

 north), and the second to illustrate polar 

 action as a whole ; this latter was obtained 

 by making a summation of prominence 

 frequency for the two zones 6o°— 90 north 

 and south. 



The simultaneous occurrence of the 

 maxima suggests that, when the promin- 

 ence action takes place at the polar regions 

 of the sun, one effect on the earth is that 

 we experience our greatest magnetic dis- 

 turbances. 



Mr. Ellis has previously stated that un- 

 usual magnetic disturbance is frequent 

 about epochs of sun-spot maximum. The 

 present inquiry indicates that not only do 

 these "great" disturbances occur at the 

 same time as the polar prominences, but 

 the spectroscopic observations of sun-spots 

 show that they take place not only " about " 

 the times of spot maximum, as stated by 

 Mr. Ellis, but when the sun-spot curve is approaching a 

 maximum and at the dates of the widened line crossings, 

 when the curve representing the " unknown " lines is on 

 the rise, and crosses the " known " line which is descend- 

 ing. At the other epoch of "crossing," i.e. when the 



IDOOO 



taaoo 



13000 



CROSSINGS 



WIDENED 

 LINES 



PROMINENCES 

 eo - -9o- "■ 



N. t 6 SAT 

 (TAcCHiNi> , 



PROPIINENCES. 

 CO"- 70* 10. 



N LAI 



tfACCHINI) 



DAYS :J 



MAGNETIC 



DISTURBANCES! 



GREAT' 



1 In referring to the curve representing the var'a- 

 tion of the mean daily areas of sun-spots, it maybe 

 noted that this is obtained by combining the mean 

 daily areas of both hemispheres of the sun. A closer 

 analysis shows, however, that this variation is not the 

 same for both hemispheres. Fr< m the year 1862, 

 when such a division of the sun's disc can be easily 

 investigated, the northern hemisphere, about the time 

 of the two last maxima, displayed double maxima 

 occurring in the years 1881 and 18S4, and in the years 

 1892 and 1895. Ab ml the time of the maximum of 

 1870 this duplicity is net so marked, although when 



compared with the curve for ihe southern hemisphere for this period, there 

 is a slight indication of a subsidiary crest in 1872. In the case of the 

 curve representing the mean spotted area for the southern hemisphere alone, 

 at all the three epochs of maximum, the curves are single-crested and 

 indicate sharply-defined maxima in the years 1870, 1883 and 1893. 



From the above it will be seen, therefore, that the actual epochs of sun- 

 spot maxima, as determined from the northern and southern hemispheres 

 respectively, are not the same, and in dealing with the curve representing 



a_^a^ 



iseoo 



18800 



Fig. 3.— Comparison showing days of "great" magnetic disimbance, polar prominences, , 

 and crossings of widened lines. (The continuous and broken vertical lines as in Fig. i.J 



curve showing the " known " lines is on the rise and the 

 " unknown " is falling, there is practically no " great " 

 magnetic disturbance recorded. 



this variation for the whole hemisphere, this fact should be borne in mind. 

 It may further be noted that the epochs of minima may.be practkally 

 considered the same for both hemispheres. 



NO. I738, VOL. 67] 



