S-tO Prof. Hansteen on the Polar Lights, 



be to him ; and experience also teaches that in the north of 

 Norway it has merely a grayish tint, and still further north is 

 not seen at all. If the aurora goes far beyond the zenith of the 

 observer towards the south, he may also there observe a dark 

 segment DCB beneath it. If single rays IH (fig. 3.) rise be- 

 tween the arch FE and theplaceof the observer C, the latter sees 

 the arch FE through the space of air KI leaning on the arch 

 FE, which is darkened by the rays IH, and sees them move 

 before the luminous back-ground like columns of smoke, and 

 with the violence peculiar to the rays of the aurora. 5. If 

 the observer in C (fig. 1.) sees the aurora reach beyond the 

 magnetic zenith, he is surrounded on all sides by the substance 

 of the polar light issuing from the earth : in this case, if the 

 development is rapid, and he stands in the open field far 

 from any extraneous sounds or noise, he will frequently hear 

 a noise resembling the buzzing caused by the effervescence of 

 a mixture of acid and alkali ; but if the aurora does not reach 

 his zenith, i. e. if he stands beyond the region from which the 

 emanation takes place, and sees it low in the north or south, as 

 in C (fig. 3.), he will not hear such a noise. It is therefore na- 

 tural that the people in the North often hear a sound attending 

 this phaenomenon, whilst the Southei'n observer perceives no- 

 thing of it ; the sound being so slight that it cannot be heard 

 at a distance. 



The properties of the polar lights mentioned above seem 

 to be inexplicable, if we assume that it is produced by electric 

 currents in the atmosphere. It seems indisputable that the 

 direction of the rays of the aurora, like that of the dipping- 

 needle, is determined by the attractive and repulsive powers of 

 the terrestrial magnetism. The phaenomenon of light seems to 

 arise when the intensity of the terrestrial magnetism has 

 risen to an unusual height, and this intensity seems to be 

 considerably weakened during the development of the polar 

 light. But we have not known hitherto any such elastic 

 fluids in the magnet, by the union of which, phaenomena of 

 light appear, as in the two opposite electricities. It is there- 

 fore still to be discovered what kind of substance it is which 

 seems at once to partake of the properties of electricity and 

 magnetism. 



In the Magazinfor Naturvidenskaberne, vol. ii. pp. 98, 99, 

 I have advanced the following hypothesis, as an attempt to- 

 wards an explanation of the electro-magnetic phaenomena. In 

 the completed galvanic circuit, the conductor is traversed in 

 an opposite direction by the opposite electricities. Every po- 

 sitive elementary particle strives to combine with a negative one; 



thus 



