30 ON TUE RECENT SECULAR PERIOD 



great features was fully equal to that in an aurora borealis of the first class, or in 

 many of the exhibitions described by the French Commission as seen at Bossekop. 

 If the number reported by the antarctic cruise is small in comparison with those 

 seen at Bossekop, during an equal period, it must be considered that in the 

 southern polar regions it was mid-summer with hardly anytbing of night, while in 

 the northern polar regions it was mid-winter with hardly anything of day. 



IX. Sound. — There is no decisive evidence that the aurora borealis is accompan in I 

 by any peadiar sound. Aware that sounds have been attributed to the aurora in 

 different countries and at different times, I have for many years listened attentively, 

 during the greater exhibitions especially, but have never been able to detect any. 

 In one or two instances, a sound was heard which, at the time, I was inclined to 

 ascribe to the aurora, but afterwards ascertained that it proceeded from other 

 sources. Let one unaccustomed to nocturnal observations, be abroad in a still night, 

 and attentively listen, and he will hear a sound which had never before arrested 

 his attention, and which he will be likely to ascribe to any extraordinary pheno- 

 menon then prevailing. He will usually liken it to the rustling of the wind through 

 dry leaves, or to a distant waterfall ; but either of these sounds may be heard on 

 almost any still night when the ear is on the alert, being nothing else than the 

 resultant of all the minute sounds which nature is ever uttering. A company of 

 my pupils were strongly impressed with the belief that they heard peculiar sounds 

 connected with an aurora borealis ; but on taking them abroad on the next clear 

 evening, and bidding them listen, they were forced to acknowledge that they heard 

 the same sound as before. Men of science who have visited countries most fre- 

 quented by these lights, as Biot, in the Western Isles, Lottin and his associates in 

 Lapland, and navigators of the polar seas, have been nearly unanimous in the 

 statement that they never heard any sound which could be certainly predicated of 

 an aurora. Judge M'Cord, of Montreal, an attentive and accurate observer, 

 informed me that he had, on one occasion, and only one, heard a sound — a "rustling 

 noise," which he attributed to an aurora then prevailing. The possibility, however, 

 that it might have proceeded from some other source is obvious ; and perhaps such a 

 conclusion is more probable than that this, among hundreds which he had observed, 

 should alone afford such a token of its presence. The popular belief in peculiar 

 noises attending these exhibitions, is said to have been extensive, particularly among 

 the Western Islands of Scotland; but scientific observers, even those who, like 

 Farquh arson, maintain that these displays are often below the clouds, make no men- 

 tion of any accompanying noise, and I incline to the opinion that the aurora is 

 not attended by any peculiar sound. 



X. Height. — The exhibitions of the aurora borealis take place usually at a great 

 but variable height above the earth. On this point different observers have held 

 widely different opinions; some, as Farquharson, Parry, and Bichardson, having 

 assigned these phenomena to the region of the clouds ; and others, as Dal ton, and 

 the greater number of philosophers, to regions of the atmosphere not less than one 

 hundred miles above the earth. On a point of such importance, it may be useful 

 to compare a few of the leading authorities. 



Mairan, about the year 1731, by comparing good observations made at Paris and 



