NATURAL HISTORY of NORWAY. 



thern lights are feldom or ever feen; the air being too far op- 

 preffed and condenfed by the intenfnefs of the cold, to force it- 

 felf upwards againfl the nitrous region, and communicate to it 

 that motion which produces the north- light, before the lower air 

 again expands itfelf by frefh fermentations." 



Thus far M. Heitman, whofe obfervations in fome meafure 

 confirm the general opinion of its being a kind of fulgur brutum, 

 or lightning without thunder; connfting, as lightning generally 

 does, of inflamed iulphureons particles, but burning with much 

 lefs vehemence. Dr. Nicholas Boerner, in his Phyfics, chap. xi. 

 p. 284. is exprefsly of this opinion, viz. " that the north- light is 

 nothing but faline, fulphureous vapours, kindled in the upper air, 

 by a change it undergoes in autumn, Ipring, and at other times, 

 when the fun has not power fufficient to rarify and difperfe thefe 

 fulphureous particles." Or, to make ufe of the words of die cele- 

 brated Wolfrus, a it is a fubitance as yet immature for lightning; 

 of which he treats in a particular diflertation; or, an imperfect 

 temper!, as he calls it in fed. 335, of his rational Reflections 

 on the works of nature." This opinion may be further corro- 

 borated by the following circumftanee : Some perfons of credit, 

 who live in this country, have afTured me, that thefe Fulgura 

 ipuria, '. are not always without a crack or found, for in a glaring 

 north-light, and calm weather, a diftinct found has been heard, 

 with an explofion in the air, like the fudden breaking of the ice. 

 Another opinion concerning the north-light, is, that it is no 

 more than a mere refraction, or reflection of a flame iffuing from 

 certain vulcanoes, which, in favour of this conjecture, are fup- 

 pofed to lie beyond Greenland, near the north-pole. But this 

 pofition is too weak to build any thing on, or to be generally 

 admitted. There are many, however, who confider the northern 

 lights only as a mere reflection, or reverberation, tho' not from 

 the flame of any vulcanoes, but from the fun itfelf, when far be- 

 low our horizon it meets with fome evaporating clouds, at fuch 

 a height as to be within the contact of the fun's beams in their 

 afcent. 



This is the opinion, for which Dr. Ventfky of Prentflau de- 

 clares in his third publication of Mifcellaneous Obfervations, 

 drawn from the celebrated M, Euler's enquiry into the north-- 



light, 



