POLAR LIGHT, Oil AURORA. 159 



those of Siljestrom( 217 ) and Bravais (18381839) in 

 Lapland, and those at Toronto in Canada (1840 1841), 

 discussed with much perspicacity by Sabine. ( 218 ) In 

 our concerted simultaneous observations made at Berlin 

 in Mendelssohn's and Bartholdy's garden, at Freiberg 

 below the earth's surface, at Petersburg, Kasan, and 

 Nicolaieff, a derangement of the magnetic declination 

 was perceived at all the stations during an aurora seen 

 at Alford in Aberdeenshire (lat. 57 15') on the 19th 

 and 20th of September 1829; and at those among 

 them at which the other magnetic elements were also 

 observed, the dip and force were also seen to be 

 affected. ( 219 ) During the fine aurora borealis observed 

 at Edinburgh by Professor Forbes, on the 21st of 

 March 1833, the magnetic inclination in the mine at 

 Freiberg underwent a remarkable decrease, and the 

 declination was so disturbed that it was hardly possible 

 to take any readings. A phenomenon which appears 

 deserving of particular attention, is a decrease of the 

 total magnetic force during increasing activity of the 

 auroral process. The results obtained by Oltmanns 

 and myself at Berlin, during a fine aurora borealis on the 

 20th of December 1806, ( 22 ) and which were printed 

 in Hansteen's " Untersuchungen iiber den Magnetismus 

 der Erde," have been corroborated by Sabine and by the 

 French physicists in Lapland in 1838.( 221 ) 



As in the foregoing careful attempt at an account of 

 the state of our positive knowledge in regard to the 

 phenomena of terrestrial magnetism, I have limited 

 myself to a simply objective representation, inasmuch 

 as theoretical views drawn by inductive reasoning from 

 analogies have not yet assumed a sufficiently satisfactory 



