December, 1903.] 



KNOWLEDGE 



277 



the following morning, its oscillations were specially 

 marked. After that they began to die away, and the 

 disturbance ended about au hour later. This was by 

 no means a magnetic storm of the first rank, but it was 

 decidedly the most striking that had been recorded since 

 1898, September, and it may fairly be regarded as dis- 

 tinctly of the second class in importance. The greatest 

 amplitude of movement in declination was 35'. 



The third groni), which I have called the Storm Group, 



TTTTXnTTTITTTTTTTTTTT 



FiQ. 3. — Greenwich Magnetic Register; Declin.ation and Horizontal 

 Force ; 190.3, October 30-31. 



came on the sun at the east limb on October 25, and 

 touched the central meridian at 10 o'clock in the morning 

 of October 31, where it is shown on the Plate. It is seen on 

 Fig. 1 near the west point. Its passage across the meridian 

 took about eighteen hours, so that it had entirely passed by 

 November 1, 4 hours. A little before it reached the meridian, 

 an extraordinarily violent magnetic storm began. It 

 commenced in the characteristic way, so often noticed, of 

 a sudden sharp twitch of the needle, first slightly to the 

 east, then strongly to the west, and back. At 13 hours 

 the vibrations of the magnet became very violent, and 

 from this time until 23 hours on October 31, changes in 

 declination exceeding a degree in magnitude were 

 frequent. By the kindness of the Astronomer Royal, to 

 whom we are also indebted for permission to reproduce 

 the solar photographs given in the text and in the 

 Plate, we are enabled to give reduced copies of the 

 Greenwich photographic registers of declination and hori- 

 zontal force from noon, October 30, to noon, November 1. 

 It will be seen tliat the spot of light thrown by the 

 horizontal force magnet ran off the barrel continually, 

 especially during the afternoon and evening of October 31, 

 and that sometimes the registers for declination and 

 horizontal force became inextricably confused together. 

 The vertical force register showed aberrations as extreme 

 during the height of the storm. The extreme range in 

 declination was more than 2°, the most westerly position 

 being registered October 31, 15 hrs. 40 min., the most 

 easterly, October 31, 19 hrs. No storm so violent has 

 been registered since that of 1882, November 17. The 

 recent storm, however, was by no means so long enduring 

 as the one of 1882 (see Figs. 3 and 4). 



The earth current register from noon on October 31 is 

 also given (Fig. 5). Tlie Greenwicli earth current registers 

 are, in the ordinary way, comiiletely spoiled by the blurring 

 caused by the City and South London Electric Railway 



during the whole time that the cars are running on that 

 line, and the genuine earth cun-ents can only register 

 themselves during the few hours of early morning when 

 the railway is at rest. But the storm of October 31 was 

 so violent that any effect from the City and South London 

 Railway was entirely overpowered. The effect of the 

 storm upon telegraphic communication the world over was 

 most pronounced. During a part of October 31, France, 

 for instance, was almost entirely isolated as regarded 

 telegraphic communication; the lines to Central and South 

 America failed first, those between Paris and the south of 

 France next, and then the lines between Italy, Spain, 

 Portugal, and Algeria. Similarly there was great inter- 

 ruption in telegraphic communication from London 

 westward to New York, and eastward to northern Europe ; 

 and in the United States the great land cable lines were 

 much affected, causing, in some localities, a total cessation 

 of business. Fine aurorae were observed, not only in 

 England, but also in the State of New York and in 

 Hungary. 



It seems to me that the appearance of these three groups 

 of spots, and the occurrence of three distinct magnetic 

 disturbances practically simultaneous with the passages of 

 the spots across the central meridian of the sun's disc, is 

 exceedingly instructive. On the one hand, it points unmis- 

 takably to a true connection between the two orders of 

 j>henomena ; the spots on the sun, and the magnetic varia- 

 tions on the earth. Next, it shows most emphatically 

 that it is not possible to take the area of the spot as a 

 measure of the intensity of the magnetic storm. The 

 three magnetic disturbances were altogether of different 

 orders. The first, that of October 12 to 13, was a respect- 

 able example of the second order ; but the spot with 

 which it was associated was quite exceptional iu size ; 

 entirely of the first rank. The second magnetic disturb- 

 ance was not only one of the first class, but an exception- 

 ally intense one of that class ; the spot with which it was 

 synchronous was large indeed but quite of the second 



Sahirdai/ Oct. 31. 





is'zifgi'ii-iio'' f ^ a' 4' ^ ^ 7" a" s' 



Fto. 4. — Greenwich Magnetic Register; Declination ami Uorizontal 

 Force; 1903, October Sl-November 1. 



rank. The third magnetic disturbance, though distinct, 

 was altogether insignificant in amount, one of the fourth 

 or fifth rate ; whilst the spot sjTichronous with it was 

 decidedly larger than the one synchronous with the gi-eat 

 magnetic storm. The question still remains which of two 



