132 BAUER— SOLAR ACTIVITY AND [April 23. 



may be seen remarkable formations of sun-spots and the conclusion 

 is drawn that there is some connection between the solar and ter- 

 restrial phenomena, especially so as similar coincidences have very 

 often occurred in the past. 



However, the connection is far from being such an immediately 

 evident one. Many cases of magnetic storms might be cited when 

 no sun-spots existed, at least on the face of the sun then visible. 

 Then again, the area of a sun-spot is no true index either of the 

 character or of the magnitude of a magnetic storm which may occur 

 at about the same time. Thus one of the severest magnetic storms 

 within the past fifty years — that of October 31 to November i, 

 IQ03 — was associated with a group of sun-spots considerably smaller 

 than that in the earher part of the month which was accompanied by 

 a minor magnetic disturbance. Attempts at a direct connection be- 

 tween individual sun-spots and individual magnetic storms have not 

 been wholly successful. While there have been a few cases — very 

 few in fact — in which an apparently immediate connection was dis- 

 covered between some striking solar phenomenon and a terrestrial 

 magnetic fluctuation, there are vastly more instances for which no 

 such individual relation existed. If, however, the subject is ap- 

 proached statistically, and the average state of the solar surface, 

 as gauged by sun-spots or other eruptive phenomena, is compared 

 with the average state of the earth's magnetism for a sufficient 

 interval of time — a year or say several months — and these average 

 values plotted, then a most striking resemblance is manifested 

 between the two sets of phenomena. The parallelism, as intimated, 

 is not so pronounced, however, for shorter intervals, for example 

 that of a month. 



The magnetic data generally used in such comparisons are the 

 ranges or ampHtudes of the daily fluctuations of the magnetic needle 

 or say the frequencies of magnetic storms. During years of high 

 sun-spot frequency, i. e., increased solar activity, the diurnal swing 

 of the needle is very appreciably greater than in years of low sun- 

 spot frequency. And likewise without question the greatest number 

 of, as well as generally the severest, magnetic storms occur in years 

 of increased solar activity. While investigations exhibit a linear 

 relationship between the average sun-spot frequencies and the 



