May 2, 1892.] 



KNOWLEDGE 



91 



vertical force by nearly 1-lOOth part. From 4b. to 7b., 

 aud also from lib. to 17b., tbe motions were large and 

 violent, tbe range exeeedmg 2° for tbe declination, and 

 1-uOtb part for tbe borizontal and vertical force. Eartb- 

 current disturbances were also recorded, corresponding 

 botb in time and magnitude witb tbe magnetic cbanges." 



Mr. AVbipple, Superintendent of tbe Kew Magnetic 

 Observatory, supplements tbis information by some addi- 

 tional notes not less interesting. " Tbe disturbance," be 

 says, " commenced about 8.30 p.m. on tbe nigbt of Satur- 

 day, tbe lltb inst." (Tbat is to say at tbe precise time, 

 so far as it is possible to fix it, wben tbe great spot began 

 to come into view at tbe east limb of tbe sun.) •• Tbrougb- 

 out tbe wbole of Sunday, ilonday, and Tuesday, tbe 

 magnet continued slowly oscillatmg tbrougb arcs of about 

 20' on eitber side of its normal position. On Wednesday 

 and Tbursday tbe vibrations were frequent, but very 

 small, partaking ratber of tbe nature of tremors." About 

 10.30 A.M. on Friday t tbe storm became violent, and from 

 tbat bour up to .5.30 a.m. of Saturday tbe oscillations of 

 tbe magnet and tbe cbanges of force were incessant, and 

 frequently enormous, tbe decbnation-needkj ranging at 

 times tbrougb almost 2^." 



It is unnecessary to multiply quotations, but a similar 

 record could bave been gatbered from any number of 

 magnetic observatories, a record sbowiug a restlessness of 

 tbe magnets beginning just as tbe spot first came into 

 view at tbe west limb, and rismg to tbe intensest excite- 

 ment just about tbe time tbat it came to the central 

 meridian and reacbed its greatest development. 



And not merely from observatories wbere tbe study of 

 delicate magnetic phenomena is made a speciality were 

 such occurrences reported. " All along the railway," 

 writes an observer in Scotland, '• the block instrument 

 bells in the railway cabins were occasionally rung as if by 

 tbe operator, and telegraphic commimication was much 

 interrupted, and in some cases even temporarily stopped." 

 Another, in the south of England, reports : " At the local 

 post office here all tbe longer lines were much affected 

 during Friday and Saturday, sometimes to an extent inter- 

 fering with ordinary messages." Nor was this effect only 

 felt in tbe British Isles ; the American and Continental 

 newspapers recorded just as striking interferences with the 

 usual action of tbe telegraphs. 



Yet a further point. -lust as the magnetic storm of last 

 February was accompanied by a fine aurora, so was tbat of 

 November, 1882. Indeed the 1882 record is the more 

 remarkable. " Aurorie of varying brilliancy," Mr. J. 

 Edmimd Clark records, " were seen at York on the 12tb, 

 13tb, 11th, loth, 17th and 18th (morning of 19th), 

 November tbe 16tb and evening of 18tb being too cloudy 

 for observation ; the 17th giving an exhibition of excep- 

 tional brilliancy." 



Records of the aurora of November 17tb are plentiful 

 enough, and no wonder, for it was the most remarkable 

 exhibition of the kin<l seen for a generation, and an entire 

 number of Knowledge might easily be filled with different 

 reports of it. It will be amply sufficient, however, for my 

 present purpose to quote tbe very brief account which tbe 

 Astronomer-Royal gave of it : — " In the evening, as soon 

 as it was dark, a brilliant aurora was seen, commencing 

 witb a bright glow of red light extending from thenorth 



* The Editor's expression, on page 70, " There is no brewing of a 

 magnetic storm, it bi-eaks out with full violence from its commence- 

 ment." was not appropriat<> to the storm of November, 188:i. It was 

 '* brewing " a good while before it burst. Similar minor disturbances 

 were continued till the spot disappeared at the west limb. 



[This seems to have been a series of magnetic storms, rather than 

 one storm. — A. C. Raxtabd.] 



t Or in astronomical time, IN'ovember 16th, 22h. 30m. 



and west beyond the zenith, interspersed witb pale green 

 phosphorescent light and streamers. At Cb. 4m. a very 

 brilliant streak of greenish light, about 20° long, appeared 

 in the east north-east, and rising slowly, passed nearly 

 along a parallel of declination a little above the moon, dis- 

 appearing at 6b. 5m. 69s. in tbe west, about two minutes 

 after it was first seen. The whole aurora had faded away 

 by about 7b., but it burst out again at lib. 4.3m., when an 

 auroral arch, witb brilliant streamers reaching nearly to 

 the zenith, was seen h'om north north-east to north-west. 

 It faded away about 12h. 10m. 



Tbe " spindle-shaped beam," as the late Mr. Rand 

 Capron called the remarkable appearance seen just after 

 six o'clock, was of itself sufficient to distinguish tbe auroral 

 displaj' of November 17th, 1882, from ordinary auronv, but 

 though it naturally attracted tbe greatest attention, the 

 other and more familiar details of the phenomenon 

 rendered it the finest seen for many years. Thus Mr. 

 •J. G. Elger speaks of it as •' certainly finer than that .seen 

 on October 2.3th, 1870." 



This second instance of tbe simultaneous appearance of 

 a great Sunspot, great magnetic disturbance, and fine 

 aurora, very materially strengthens the argument for a 

 true cormection between the three orders of phenomena. 

 Let us push the enquiry a step further. 



Tbe third aud fourth spots as to area during tbe period 

 covered by tbe Greenwich record were upon tbe sun at tbe 

 same time. Group No. 72G of the Greenwich series was 

 first seen on tbe extreme east limb on April 10th, wben it 

 was only of small size. It began on April ICtb, however, 

 to develop very fast, and the group which bad an area of 

 2.38 millions of square miles on April 15th, on April ■18tb 

 covered 1020 millions, aud a second great outbreak had 

 added more than 1000 millions more by April 21st. The 

 group reached tbe west limb upon April 23rd. 



Group No. 729 followed No. 720 at an interval of aliout 

 30° of solar longitude, aud was about 10° further south in 

 solar latitude. It was already a giant spot wben first seen at 

 the east limb ou April 13tb, its area being 1340 millions of 

 square miles. It increased steadily up to April 16th when 

 it covered 2430 millions of square miles, and after suffering 

 a slight decrease it reached a second maximum of 2490 

 milhons on April 21st. 



Had tbe magnets any record of distm-bance to show ? 

 Yes, and a double one; tbe first on April 16tb, wben 

 Groitp No. 726 was beginning its wonderful development 

 and Group No. 729 had reached its first maximum ; tbe 

 second on April 20tb, lastiug till April 21st, simultaneous 

 with tbe second development of Group No. 720, and the 

 second maximum of Group No. 729. It is scarcely neces- 

 sary to quote at length tbe official descriptions of this 

 storm. I extract two sentences only from the account 

 which tbe Astronomer-Royal gave : '' Tbe total spotted area 

 was about double tbat of the greatest spotted area shown 

 on any of the Greenwich photographs previous to this out- 

 burst " ; and " since tbe great disturbances of 1872, 

 February 4tb, and those of October 4tb of the same year " 

 (both, I should remark, before .luly, 1873, when tbe Green- 

 wich Sunspot record began), " no magnetic storm has been 

 recorded equal to tbis." 



In a period of nearly nmeteen years, therefore, we have 

 three magnetic storms which stand out pre-eminently above 

 all others during tbat interval. In that same period wc 

 have three great Sunspot displays — counting the two 

 groups of April, 1882, together — which stand out with 

 equal distinctness far above all other similar displays. And 

 we find that the three magnetic storms were simultaneous 

 with tbe greatest development of tbe spots. Is there any 

 escape from the conclusion that tbe two bave a real and 



