1904- No. 2. THE DIURNAL VARIATION OF TERRESTRIAL MAGNETISM. ; 



be opening for the study of the atmospheric-electric phenomena in the 

 development of the so-called »Ion Theory'«, which is likely to open up 

 new paths in many directions. 



Side by side with a close investigation of the bearing-capabilities of 

 this theory, it also seems to me desirable to examine minutely into the 

 possibility" of the existence in the atmosphere of sharply-defined electric 

 currents of variable direction and force. Professor Birkeland^ believes 

 that he has directly proved the existence of such currents in the higher 

 strata of the atmosphere; and Professor A. Schuster- points to the 

 presence of a system of electric currents in the atmosphere as the most 

 natural explanation of the diurnal variation of the terrestrial-magnetic ele- 

 ments. This view is also held by Geheimerath von Bezold^ and Pro- 

 fessor Ad. Schmidt* of Potsdam. Hr. von Bezold even goes so far as 

 to imagine a connection between the diurnal variation of terrestrial magne- 

 tism and certain meteorological phenomena, for he says : 



»Dagegen kann man sich bei genauerer Betrachtung der hier geschil- 

 derten Erscheinungen kaum des Gedankens erwehren, dass zwischen der 

 täglichen Variation des Erdmagnetismus und der allgemeinen Cirkulation 

 der Atmosphaere doch irgend ein, wenn auch vorerst noch dunkler Zusam- 

 menhang bestehen müsse'*. 



These words seem to me to contain a ver^- far-reaching suggestion; 

 for it is evident that if a decided connection can be proved between the 

 normal meteorological conditions and the normal terrestrial-magnetic con- 

 ditions, there is ever}- reason for also expecting a kind of connection be- 

 tween the deviation from the normal conditions, or between changes in 

 the weather and magnetic perturbations. 



The investigations which Professor Birkeland is at present carrying 

 on, will certainly contribute largely to the elucidation of this question; 

 and I understand that work in a similar direction is being done in many 

 other quarters, though perhaps not always with the conscious aim of 

 directly seeking a connection between the magnetic and the meteorological 

 phenomena. 



* Expédition Xorwégienne de 1S99 — 1900 pour l'étude des aurores boréales. Résultats 

 des recherches magnétiques, par Kr, Birkeland. Videnskabsselskabets Skrifter. I. 

 Math,-naturv. Klasse. 1901. No. i. Christiania. 



- A. Schuster. The Diumal Variation of Terrestrial M^netisrn. Phil. Trans, of the 



Royal Soc. of London. Vol. 180 A. pp. 467 — 516. 

 ' W. von Bezold. Zur Theorie des Erdmagnetismus. Sitzungsberichte d. k. Preuss. 



Akad. d. Wissenschaften zu Berlin. Bd. X\'1I1, 1S97, pp. 414 - 449. 



* Meteorologische Zeitschrift. Bd. XIX, 1902. p. 94. 



