720 THE AURORA BOREALIS, 



No greater darkness than usual was ever observed before a 

 display of the aurora, such as has been observed in lower 

 latitudes for hours before a display. 



The dark appearance between the display was absolutely an 

 effect of contrast. 



A spectroscope showed only one clear line at the limit of 

 yellow and green — the same line which has been so often seen. 



Dr. Borgen says, " We have never seen a trace of the weak 

 *' lines in blue and red, which were observed so distinctly with 

 " the same spectroscope on October 25, 1870, after the return 

 " of the Expedition." 



In accordance with this we have never seen the aurora of any 

 other colour than that of greenish yellow. 



Frequently during the aurora, observations were made to 

 determine whether there were any striking disturbances of the 

 declination accompanying the display. Only once, during the 

 term day of the 5th January, at same time with aurora, there 

 was an important disturbance, and another term day showed an 

 extraordinary disturbance of the needle, but there was great doubt 

 whether the aurora was the cause of it. 



Exact and extended observations on the simultaneous disturb- 

 ances of all three elements of the earth's magnetism within the 

 Polar regions as well as in mean latitudes would greatly add to 

 our knowledge of the aurora. 



10. Observations of Aurora, made during the Austro-Hun- 

 GARiAN Expedition, by Lieut. Weyprecht. 



(From Petermann's Geograph. Mittheilungen, Jan. 1875.) 



'^ The most beautiful and interesting phenomenon in these 

 parts, the only change in the solitude of the long winter night, is 

 the Aurora Borealis ; no pen or brush can describe the glory and 

 beauty of this phenomenon in its greatest intensity. In February 

 1874 we had an Aurora that stretched like a grand broad stream 

 of fire over the zenith from west to east, and with the velocity 

 of lightning waves of light of considerable intensity in prismatic 

 colours darted from one side of the horizon to the other. At the 

 same time it lightened and flashed from the southern horizon up to 

 the magnetic pole ; it was the most magnificent firework display 

 that nature has ever here presented to our sight. 



" I shall later give proofs, with data, that the intensity of the 

 Aurora phenomena difiers in the different parts of the Arctic 

 regions independently of the geographical latitude, and that the 

 region in which we were is' a region of greatest intensity. In a 

 clear sky one could almost uninterruptedly see at least traces of it. 

 In the second winter I caused the officers who were making 

 meteorological observations to keep an * Aurora journal ;' this, 

 however, produced very little positive information, and was there- 

 fore discontinued. 



" The phenomenon defies all description and any systematic 

 classification, it shows constantly new forms and clisnges every 



