190 On the supposed irifluence of' the 



nication with some illustrations necessary to point out its im- 

 portance. 



" Since the commencement of the last century, several natural 

 philosophers, among others Celsius and York, (a misprint, we 

 presume, for Hiorter) had remarked that the appearance of 

 the Aurorae Boreales ahvays occasioned in the magnetic needle 

 irregular and very sensible movements, a certain proof that 

 they attj'ibuted to magnetism the phenomena of' these Auroras, 

 At Paris, Father Cotte and Cassini put it beyond a doubt that 

 the Aurorae Boreales exercise a magnetic influence even in our 

 climate, whatever be the distance which separates us from the 

 polar regions. But M. Ar ago has gone much Jarther. He is 

 the first person who has maintained that not only do the Aurora; 

 Boreales impress movements on the needle wherever they are 

 visible, and wherever also they might be seen if the clouds 

 did not conceal them ; but that this influence extends much 

 farther, and that even where they are not visible from their 

 not passing the horizon, they still manifest themselves in the 

 motions of the magnetic needle. 



" This assertion has been keenly controverted, chiefly in Eng- 

 land, and particularly by Dr Brewster of Edinburgh ; and our 

 celebrated natural philosopher (M. Arago) in order to esta- 

 blish the truth of it, has for some years marked at Paris, where 

 the Aurorae Boreales are no longer seen, the days on which they 

 ought to have been perceived in higher latitudes. Hitherto his 

 predictions have been airways Jbund exact, but a singular ex- 

 ception took place about two years ago. On the 29th March 

 1826, between eight and ten o'clock p. m. in very clear weather, 

 the magnetic needle in the observatory of Paris exhibited the 

 most distinct movements, in consequence of which M. Arago 

 had anncmnced that an Aurora Borealis had taken place in 

 the north. Hitherto this prediction had not been verified, 

 and the English philosophers saw in this the ground of a 

 grave objection. But Mr Dalton''s letter actually contains 

 the account of an Aurora Borealis which happened on the 29th 

 March 1 826, exactly between eight and ten o'clock in the even- 

 ing. This Aurora, whose height was not very considerable, 

 (three leagues if we rightly understood it), formed a very large 



