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during, a storm. The telluric currents cease when one end of the 

 line is isolated; they are only manifested in single lines which have 

 their return to the earth, but they may affect submarine cables, and 

 they vary in direct ratio with the length of the line. 



Balfour Stewart, in 1869, compared the earth to the center of a 

 Ruhmkorff's coil, of which the circuit is completed in the higher 

 strata of the atmosphere. Electric movements are hence produced 

 in these higher strata when terrestrial magnetism or the telluric cur- 

 rents undergo rapid variations. 



The aurora is supposed to be a purely terrestrial phenomenon, 

 without regard to outside influences. The position of the earth in 

 its orbit has no influence on the movements of the aurora. The 

 movement of the earth from east to west is not the prevailing one of 

 the aurora; the inverse movement is more frequent. 



The magnetic theory of the aurora must now yield to the electric 

 theory of its cause. We hope to show in a future paper the intimate 

 relation of magnetism and electricity, but the subject is too vast at 

 this juncture to examine. Halley, in 1716, thought the aurora due 

 to luminous magnetic vapors, but electro-magnetism was then un- 

 known. Dalton, in 1793, and Biot, in 1820, thought it was pro- 

 duced by ferruginous particles in the air, the dust of volcanoes, like 

 that which caused the " red sunsets " several years ago from a vol- 

 canic eruj)tion in Java. Van Baumhauer, in 1840, thought auroras 

 due to the fall of cosmic dust, becoming incandescent when it entered 

 the earth's atmosphere, as in the case of meteors and falling stars. 

 Toeppler, as late as 1872, supported this idea, and even supposed the 

 halo around the moon due to the same cause. 



The electric theory seems destined to supersede the cosmic, optic, 

 and magnetic theories. Canton, as early as 1753, pointed out the 

 close analogy between auroras and the light of electric discharges 

 produced in very rarefied air; he recognized also the fact that 

 a tube of such air becomes luminous when moved about near a 

 charged conducting body. In his view the aurora was but the 

 form which storms take in polar regions. So far he was very nearly 

 correct. 



The ideas of Canton were adopted by Priestley, Eberhard, 

 Frisi, Pontoppidan, Benjamin Franklin, and others, but without 

 making much progress. A very similar opinion was adopted by 

 Fischer in 1834, whose theory was that auroras were caused by elec- 

 tric discharges diie to the positive electrization of the atmosphere; 

 these discharges being produced at the moment when the electric 

 equilibrium is re-established between the atmosphere and the earth, 

 by the intermediary of particles of ice floating in the air. This was 

 followed by the theories of Dove, de la Kive, Lemstroem, and others, 



