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On the late Periodical Visitation of the Aurora Borealis in 

 North America. By Professor D. Olmsted. 



At the meeting of the American Association for the ad- 

 vancement of Science, in August 1850, Professor D. Olmsted 

 read an interesting Memoir on the Aurora Borealis, of which 

 the following is an abstract. 



The leading object of this paper, the Professor says, is as 

 follows : — 



1. To establish the fact, that we have just passed through 

 an extraordinary period of auroras (to which I venture to give 

 the name of Visitation)^ which commenced in 1827, and closed 

 in 1848. 



2. To determine the characteristics by which these exhibi- 

 tions of the aurora differ from the ordinary exhibitions of the 

 same phenomenon, and to place on record a full and accurate 

 description of several of the most remarkable, as materials 

 for comparison in future visitations. 



3. To establish, by an extensive collation of observations, 

 the laws of the aurora borealis. 



4. To determJie the origin of the aurora, and to assign the 

 true cause of the phenomena. 



In order to establish the reality of the occurrence of an 

 extraordinary visitation of the aurora within the period 

 assigned, we first examine all the facts of the case, com- 

 prising a complete history of the phenomenon for the period 

 in question ; and, secondly, compare the exhibitions of this 

 period with the ordinary displays of the aurora for the same 

 length of time, attempting to prove that, during the period 

 called a " visitation^'' the auroras greatly exceed the ordinary 

 exhibitions of the meteor, in number, in splendour, in pecu- 

 liar combinations of form, and in a progression which marks 

 a beginning, middle, and end. 



The laws of the aurora borealis, as determined by an 

 extensive induction of facts, chiefly gathered from personal 

 observations, we endeavour to shew to be the following,— 

 comprehending both such as are generally admitted to be the 



VOL. LI. NO. Cn. — OCTOBER 1851. U 



