70 



KNOWLEDGE 



[Apbil 1, 1892. 



spots are able to exercise a special and indindual influence, 

 we find there is still a difference of opinion. We may 

 therefore hopefully look to the record of spots like that of 

 November, 1882, or of the February just past, for informa- 

 tion on this point, for we naturally expect spots so 

 gigantic in size will be the most powerful in influence. 

 ( To be continued, j 



ON THE CONNECTION BETWEEN SUNSPOTS 

 AND MAGNETIC STORMS. 



By A. V. Raxyakd. 



THE lower picture on our Plate represents a large 

 Sunspot, photogi'axjhed by M. .Jaussen, on a scale 

 of nearly five feet to the sun's diameter. Its 

 irregular form is characteristic of a period of sun- 

 spot maximum disturbance such as wc have now 

 entered upon. During such periods the willow-leaf or 

 rice-grain structure of the photosphere becomes rounded 

 and less strikingly distinct than at a period of minimum 

 sunspot development. At all times a mottling of the 

 photosphere is recognizable, i^roduced by the haziness or 

 smudged appearance of the grains or cloudlets in certain 

 areas, while between the hazy areas the brilliant little 

 cloudlets and the small black spaces between them are 

 more distinctly visible, and are seen to be arranged more 

 or less parallel to one another. As a period of sunspot 

 maximum arrives, the character of the whole photo.sphere 

 seems to alter. The change is not merely confined to the 

 latitudes within 10° of the solar equator, where the spots 

 appear, but extends to the neighbourhood of the solar 

 poles. Similarly the prominences which appear in all 

 heliographic latitudes from the poles to the equator change 

 their character. 



We are at present only in a position to observe and 

 collate facts, and we seem to be very far from miderstanding 

 the great periodic changes going on before us. 



There is evidently a close connection between the develop- 

 ment of spots on the sun's surface and the swaying of the 

 earth's magnetic axis. More than one popular writer has 

 spoken of this connection as pro\"ing that the sun is 

 magnetic ; and that solar storms sway its magnetic axis — 

 and, further, that every motion of the great solar magnet is 

 accurately followed by a corresponding motion of the 

 magnetic axis of the planets, which bow and swing, always 

 keeping parallel with the axis of the great central magnet. 



But the earth's magnetic axis revolves about the earth's 

 axis of rotation once in twenty-four hours describing a circle 

 amongst the stars of nearly 20" radius. If then, the 

 earth's magnetic axis and the sun's magnetic axis were 

 permanently parallel, we should have to assume that the 

 sun's magnetic axis travels round a line which is not the 

 sun's axis of rotation in a period equal to the earth's period 

 of rotation, which seems highly improbable. 



There is considerable difficulty in conceiving of a hot 

 gaseous body like the sun being magnetic. The difficulty 

 occurred to Sir Isaac Newton, who, in a letter written on 

 the 16th of April, 1681, wrote: " Concerning the experiment 

 that a magnet loses its magnetism by heat, some have 

 indeed supposed the sun to be cold, but I believe Mr. 

 Flamsteed is not of this opinion, for they may as well 

 affirm culinary fire to be cold. For we have no argument 

 of its being hot, but that it heats and biu-ns thmgs that 

 approach it, and we have the same argument of the sim 

 being hot. Were we ten times nearer him, no doubt, we 

 should feel him a hundred times hotter, for his light 

 would be a hundred times more constipated, and the 

 experiment of the burning-glass shows that his heat is 



answerable to the constipation of his Ught 



The whole body of the sim therefore must be red hot, and 

 consequently void of magnetism, unless we suppose its 

 magnetism of another kind from any we have, which Mr. 

 Flamsteed seems inclined to suppose." 



It is possible that though the sun itself may not be 

 magnetic, it may act as a magnetic body because it is 

 surrounded by a magnetic envelope or region where its 

 gaseous constituents are precipitated into solid or liquid 

 magnetic particles. During the past year Professor Dewar 

 has shown that oxygen becomes strongly magnetic when 

 liquefied at a temperature of - 180° Cent. The vapoursof iron 

 when precipitated in the comparatively hot lower regions of 

 the corona, would also form a cloud of magnetic fog or 

 dust. There is some evidence, in the forms of the coronal 

 streamers seen in the neighbourhood of the sun's poles, 

 that the coronal particles are magnetic, and tend to arrange 

 themselves along lines of force, as if the whole sun had a 

 magnetic axis, nearly but evidently not accurately, 

 coincident with the sun's axis of rotation. 



The corona is far from being accurately symmetrical 

 with respect to the sun's axis of rotation ; it is denser in 

 parts, and has projecting rays or structures which extend 

 to a great distance from the sun, especially in the sun's 

 equatorial regions. On the above theory we should expect 

 to find the magnetic region similarly unsymmetrical, and 

 a body passing round the sun, near to the plane of the solar 

 equator, would be subject to very unequal disturbance 

 from the magnetic particles of the corona. This seems to 

 tally with the facts observed — for the greatest magnetic 

 storms have generally taken place when a large spot 

 has been seen near to the centre of the sun's disc. We 

 know very httle at present as to the connection between 

 the corona and sunspots, or as to how far the corona 

 extends — some of its larger structures may extend as far as 

 the earth's orbit, or as far beyond onr orbit as the zodiacal 

 light extends. There is no evidence that large coronal 

 structures exist over large sunspots, but there is evidence of 

 an intimate connection betwen the general development 

 and arrangement of the parts of the corona and the 

 spottiness of the sun's surface, as well as between the 

 development of large prominences and sunspots. 



The sudden manner in which these magnetic storms 

 commence seems rather to indicate that the earth plunges 

 into a magnetic or auroral region, than that the magnetic 

 equilibrium of the whole solar system is suddenly disturbed. 

 There is no brewing of a magnetic storm, it breaks out 

 with full violence from its commencement. 



ILcttcrs. 



— I * I — 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



STELLAR SPECTRA. 

 To the Editor of Knowledge. 



SiR^ — 'With reference to Mr. Monck's remarks on the 

 spectra of binary stars m Knowledge for March, 1892, 

 2 4 seems to be identical with Lalande 220. I find that 

 the star in the Draper catalogue is identical with Lalande 

 221, which lies about 8' 25" north of the binary. Both 

 stars were rated 7|- magnitude by Lalande, and are 8 

 magnitude in Harding's atlas. They he closely soutli 

 prect'dinij the Ij magnitude star a Andromedse. The 

 spectrum of O 2 4 was sent to me by Professor Pickering. 



With reference to /a'- Bootis my authority for its 

 spectrum is Professor Pickering, who kindly sent me the 



