194 On the supposed influence of the 



his magnetical observations, he finds that the needle was not 

 " true to the pole." All this is very well so far as it goes ; 

 but as M. Arago has established a hypothesis on the authority 

 of these observations, and as he maintains this hypothesis with 

 so much keenness as to identify it with his own reputation, we 

 humbly suggest to him, that it is his duty as a man of science 

 to publish these observations without delay. Some philoso- 

 phers will thus be indulged with the luxury of prediction which 

 he now monopolizes, while others will enter upon the more 

 useful occupation of drawing up a list of all the irregular 

 agitations of the needle, and classing them according to their 

 magnitude or their duration, and of comparing them with the 

 Aurorse Boreales which they have become acquainted with 

 either by reading or by observation, and with the more strik- 

 ing meteorological phenomena of the atmosphere. Until this 

 is done, philosophers are entitled to regard M. Arago"'s deduc- 

 tions as little more than the special pleadings of a party in- 

 terested in the establishment of a favourite hypothesis. 



In order to illustrate the force of these observations, we 

 shall give an example of M. Arago's mode of reasoning ; 1st, 

 when he has received information respecting an Aurora ob- 

 served in Scotland ; and, 2dly, when he predicts the existence 

 of one from his magnetical observations. 



1. Dr Coldstream and Mr Foggo of Leith observed on the 

 17th August 1825, at 10^ p. m. a display of the Aurora Bo- 

 realis, which was " neither vivid nor long-continued, and pre- 

 sented only the usual appearance of that meteor." 



Upon examining his magnetical observations, M. Arago 

 finds that there was no agitation whatever in the needle that 

 evening^ and it had then its ordinary position. But he finds 

 that at half past eight o''clock in the morning, 13J hours be- 

 fore the Aurora began, *' the declination of the needle was 5' 

 greater than the mean of the month at the same hour. Here, 

 then, the Aurora takes place at Leith on the 17th August, 

 and it is admitted that during its existence the needle is still. 

 This is no doubt a stubborn fact, but such is the ingenuity of 

 hypothesis, that M. Arago " suspects that this was the termina- 

 tion of an Aurora Borealis of the day." If the suspicion were 



