132 COSMOS. 



of his being invited by the Royal Society of London to ex- 

 plain the great meteor of the 6th of March, 1716, which was 

 seen in every part of England. He says, " that the meteor 

 is analogous with the phenomenon, which Gassendi first 

 designated in 1621 by the name of Aurora borealis" 

 Although in his voyages for the determination of the line 

 of variation, he advanced as far south as 52, yet we learn 

 from his own confession, that he had never seen a northern, 

 or southern polar light before the year 1716, although the 

 latter, as I can testify, is visible in the middle of the tropical 

 zone of Peru. Halley, therefore, does not appear from his 

 own observation to have been aware of the restlessness of the 

 needle, or of the extraordinary disturbances and fluctuations 

 which it exhibits at the periods of visible, or invisible north- 

 ern or southern polar lights. Olav Hiorter and Celsius at 

 Upsala were the first who, in the year 1741, and therefore 

 before Halley's death, confirmed by a long series of measure- 

 ments and determinations the connection, which he had 

 merely conjectured to exist between the appearance of the 

 Aurora borealis and a disturbance in the normal course of the 

 needle. This meritorious investigation led them to enter 

 into an arrangement for carrying on systematic observations 

 simultaneously with Graham in London, while the extra- 

 ordinary disturbances of variation, observed on the appear- 

 ance of the Aurora, were made subjects of special investiga- 

 tion by Wargentin, Canton, and Wilke. 



The observations which I had the opportunity of making, 

 conjointly with Gay-Lussac, in 1805, on the Monte Pincio 

 at Rome, and more especially the investigations suggested by 

 these observations, and which I prosecuted conjointly with 

 Oltmanns during the equinoctial and solstitial periods of 



parts) than at the equator, the inner luminous fluid (that is, the mag- 

 netic fluid), seeks at certain periods, more especially at the times of the 

 equinoxes, to find itself a passage in the less thick polar regions through 

 the fissures of rocks. The emanation of this fluid is, according to 

 Halley, the phenomenon of the northern light. When iron filings are 

 etrewn over a spheroidal magnet (a terella), they serve to show the 

 direction of the luminous coloured rays of the Aurora. ' ' As each one 

 sees his own rainbow, so also the Corona appears to every observer to be 

 at a different point" (p. 424). Eegarding the geognostic dreams of an 

 intellectual investigator, who displayed such profound knowledge in all 

 his magnetic and astronomical labours, see Cosmos, vol. i, p. 163. 



