THE 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOTJBNAL OF SCIENCE. 



SUPPLEMENT to YOL. XVII. EIETH SEEIES. 



LVL On the Magnitude of the Unipolar Induction of the 

 Earth By E. Edlund, Professor of Physics at the Royal 

 Academy of Sciences of Sweden*. 



§1. 



I ENDEAVOURED to prove in a previous memoir f that 

 the unipolar induction produced by the rotation of the 

 earth upon its axis is the principal cause of the electricity of 

 the air, of thunder, and of the aurora borealis. If, now, for 

 a long time, these telluric phenomena have failed to find 

 their explanation in this induction, the reason undoubtedly 

 lies in the incorrect notions which have been formed as to its 

 real nature. The old theory of unipolar induction is, in 

 fact, in flagrant opposition to the principles of the mecha- 

 nical theory of heat, and it was consequently impossible 

 that it could be true. It was necessary then, first of all, to 

 establish a new theory of unipolar induction, in which it w T as 

 of course necessary to show not only that it explained all the 

 known phenomena of unipolar induction in their details, but 

 that, on the other hand, it is in perfect harmony with all that 

 is known of the manifestations of electricity. This is what I 

 have endeavoured to do in the memoir referred to. The theory 

 once formulated, the application to the earth is easy. Pro- 

 bably no one will doubt for the future that unipolar induction 

 plays an important part in the production of the electric phe- 

 nomena in question ; but since, as far as our knowledge of it 

 extends at present, the effects of this induction have shown 



* Translated from a separate impression from tlie Konyl. Svenska 

 Vetenskaps-Akademiens Handlingar, Bd. xx. No. 5, communicated by 

 the Author. 



t " Researches upon Unipolar Induction, Atmospheric Electricity, and 

 • the Aurora Borealis," Memoires de V Academie royale des sciences de Suede, 

 vol. xvi. no. 1 (1878) ; Annates de Chim. et de Physique, vol. xvi. p. 49 

 (1879) ; Phil. Mag. vol. vi. p. 289 (1878). 



Phil. Mag. S. 5. No. 109. Suppl. Vol. 17. 2 L 



