THE AURORA BOREAI-IS. 271 



zon ; it being then really in a more condensed slate, and appairently so' 

 also on account of being seen obliquely by the observer. 



It has already been stated that the magnetic needle is constantly dis- 

 turbed during an auroral display, and that too in proportion to its ac- 

 'tivity. A most intimate relationship had, long, been more than sus- 

 pected as existing between electricity and magnetism. Electricity was, 

 for instance, known, under favoiable circumstances, to communicate and 

 to destroy magnetism. But since 1820, when Prof. Oersted found that 

 an electric current causes the magnetic needle to deviate from its posi- 

 tion in reference to the meredian, every new discovery in these two col- 

 lateral branches of science, has only shown the intimacy to be the more 

 close, until, in the hands of Faraday, the proof that they are but modi- 

 fied phenomenon of one great material agent, and that they are perfectly 

 reciprocal, the one capable of producing the other, has become complete. 

 Now repeated observations, made within the last quarter of a century, all 

 go to prove that the needle is not only disturbed during the display, but 

 especially so when the streamers are brilliant, thus showing that it is 

 affected precisely as if electricity were in motion, and corresponding in 

 the extent of its disturbance to the intensity of those movements. — 

 The mean disturbance of the needle being, moreover, eastward, the ef- 

 fect is the same as if electric currents moved above the earth from the 

 pole towards the equator, which is also the apparent direction of the au- 

 roial movements. 



Dr. Dalton has, also shown, what has since been verified in innu- 

 merable instances, that, not only are the coronas, when they exist, inva- 

 riably found to occupy the place in the heavens to which the elevated 

 pole of the dipping needle is directed, but the "luminous arches" are 

 perpendicular to the magnetic meridian, or parallel to the magnetic equa- 

 tor, which makes an angle of about 12° with that of the earth. This 

 remarkable obedience to magnetic forces must certainly be regarded as 

 something more than accidental. 



9. Regarding, therefore, the aurora, as we must, as an electrical dis- 

 iplay, it is yet necessary to state the different explanations offered by dif- 

 ferent philosophers as to the mode in which the free electricity is supplied 

 and made to produce the visible effects of the aurora. 



Canton supposed that the electricity flashed from positive to negative 

 clouds; but then, it may be asked, why is the direction of" the auroral 

 flashes always from polar towards equatorial parts, unless we make the 

 bold assumption that the electrical relations of clouds depends upon 

 those of latitude? And vvhy is the aurora not as frequent and brilliant 

 in equatorial as in polar regions ? Beccaria supposed that the electric 



