130 



Dr. W. Huggins. 



nomer Royal, writing of the magnetic activity of the year 1882, says : 

 " The month of November, which was characterised by the appearance 

 of a very large snn-spot, being particularly disturbed with remarkable 

 magnetic storms on November 17, 19, and 20, and many interesting 

 cases of lesser disturbance."* 



We can scarcely doubt but that similar electric disturbances of 

 exceptional magnitude accompany the formation of the prominences ; 

 indeed these phenomena may themselves be, in part at least, electric 

 discharges analogous to terrestrial aurorae.t However this may be, 

 we can scarcely doubt that large electric disturbances accompany 

 them. Tacchini takes the view that electricity plays a chief part 

 in the prominences, and believes that he is able to show a connexion be- 

 tween these phenomena and corresponding changes in the magnetism 

 of our globe. £ 



Hitherto in our discussion of the forces which may be active in the 

 corona, we have taken account only of the influence of electrical 

 changes which take place upon the sun. Now these changes at the 

 sun make themselves felt upon the earth ; we may then well suppose, 

 with a high degree of probability, that the earth,§' and especially the 



of the conjecture thrown out in the last sentences of the text, that the corona was 

 formerly of larger extent, and that it will continue to diminish. — August 20, 1885. 



[My attention has been called this day to a paper by Prof. O. Reynolds, " On the 

 Electro-dynamic Effect which the Induction of Statical Electricity causes in a 

 Moving Body. This Induction on the part of the Sun a probable Cause of 

 Terrestrial Magnetism." "Mem. Lit. and Phil. Soc.,"^ Manchester,, vol. v, 3rd Ser., 

 p. 209.— Sept. 29, 1885.] 



* Report of the Astronomer Royal, 1883", p. 13". 



f See Balfour Stewart, " Proc. Roy. Inst.," vol. iv, p. 60. 



X " Reale Accademia dei Lincei (March 1, 1885), S.N., vol. i, p. 181. Tacchini 

 says : — " Ci'6 viene anche a corroborare l'bpinione mia e di qualche altro, che cioe 

 nel fenomeno delle protuberance sol'ari Felettricita attia una parte rilevante, da 

 dovere forse considerare non poche di esse come fenomeni puramente ellettrici, come 

 aurore polari, capaci di indurre sul nostro globo i correspondent! disturbi mag- 

 netici noi possiano intanto considerare come cosa assicurata alia 



scienza, che il fenomeno della maiehie solari, quelle delle protuberanze ed il mag- 

 netismo terrestro variano cosi di accordo." 



At the same sitting Professor Respighi toot a different view (p. 174) and stated 

 he did rot consider the prominences to be of a nature- to occur in periods, and that 

 he could not admit a connexion between the maxima and minima of the prominences 

 and the elements of terrestrial magnetism. At the following sitting, March 15 

 (p. 228) Tacchini replies to the objections of Respighi, and endeavours to show that 

 Respighi has been influenced by his preconceived views of the nature of spots and 

 prominences. 



§ Mr. Broun, in his discussion of the variations of the earth's magnetism (" Proc. 

 Roy. Soc," vol. xxiv, p. 231), says : — " It is shown that those changes (in 1844 and 

 1845) occur at intervals of twenty-six days, or multiples of twenty-six days. . . 

 As this period is that of the sun's rotation relatively to the earth, it appears to 

 follow that the earth has some action on the sun, or (more probably) on some ray- 

 like emanation from the sun, which causes these changes in the earth's magnetism." 



