PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. V. 



653 



There is one circumstance, it is true, that may seem remarkable in this storm, namely, that it was 

 not repeated on the following day, as is generally the case with powerful magnetic storms in the polar 

 regions. On the contrary, calm supervened very quickly, and the next day was very quiet. 



At Dyrafjord, however, we find the storm repeated with diminished strength the day after as well, 

 n the usual manner. 



It should be remarked, however, that it was not until two days later that the above-mentioned 

 sun-spots reached the central meridian of the sun. It is well known that several scientists have thought 

 hey could show that powerful perturbations do not as a rule occur until from 40 to 50 hours after the 

 >assage of the corresponding sunspot over the central meridian. If, therefore, we apply this here, it 



Earth- currents and magnetic elements, 19-20 May, 1910. 

 Fig. 244. 



ould appear that the magnetic storm came about 4 days too early. On the 23rd May, when, according 

 > this manner of looking at the question, the influence of the group of sun-spots might be expected, 



was very calm magnetically. But on the morning of the 24th, as mentioned above, powerful storms 

 ice more occurred. It thus appears to be difficult to deduce the magnetic storms from the sun-spots 



the usual manner; but on the other hand the above-mentioned difference in time may obviously be 

 garded as an average value of a large number of cases, and in reality the connection between sun- 

 wfe and magnetic storms is not so simple (cf. Art. 98). It is interesting to see that Dr. ANGENHEISTER 

 is believed he can prove a greater accordance between the appearance of the sun-faculae and the mag- 

 i;tic storminess on the earth in the month under consideration ( l ). 



The earth-current registerings will be discussed in the next chapter. As the magnetic disturbances 

 e exactly repeated in the earth-current curves, the reader is referred, as regards the latter, to what 



(') Cf. Angenheister's "Die Island-Expedition im FrOhjahr 1910. Die erdmagnetischen Beobachtungen. Nachrichten der K. 

 Ges. d. Wiss. zu Giittingen, Math.-phys. Kl. 1911. 



Birkeland. The Norwegian Aurora Polaris Expedition, 10021903. 



83 



