8 NATURAL HISTORY of NORWAY, 



light, which is to be found in the fecond part of the Hiftoire de 

 V Academie. This hypothecs requires the following concurrence 

 of caufes ; firft, there muft be vapours in the upper regions of 

 the air ; next, fome clouds of that fort, and thefe at a vaft height, 

 and in the north; and they mull not only emit vapours, but be 

 illuminated and irradiated by the fun, when it is invisible to us; 

 and of confequence, the fun muft be vifible to us at fuch time, 

 if we flood as far above the horizon as the faid clouds. And 

 laflly, there muft be a north-wind in the fame upper region of 

 the air to fet it in motion, and to give a difpofttion to the fi- 

 gures, which fo fuddenly change their -appearance. It is porlible, 

 that the experience of pofterity may fuggeft fomething more 

 probable. 

 The author's If I may be allowed, or expected, to add any opinion of my 

 cerSng the " own on this problematical fubjed ; it may perhaps be not more 

 12 ' improbable than what hath been already alleged, if we admit, 

 that the original caufe of the north-light lies in the electricity of 

 the etherial air; and, confequently, that it has exifted at all 

 times, and in all places, tho' not vifible to us, without a concur- 

 rence of fuch concurrent circumftances and junctures, as I fhall 

 here exhibit. It is not above twenty years, flnce the electrical 

 experiments have become generally known, and as they have 

 excited the attention of all lovers of natural knowlege, they have 

 likewife filled them with hopes, that this difcovery would open a 

 way to the folution of many more myfteries in nature. I flatter 

 myfelf with the fame expectation; but the firft experiment of 

 any importance, which has occurred to me, relates to this very 

 point of deducing the north-light from the electrical, feeble, and 

 fubtile fire of the air, which by means of the more rapid circum- 

 volution of the globe on its poles, or axis, excites a more vehe- 

 ment concuiTion, or agitation, in the air of the northern climates, 

 and thus difplays the electricity of the ethereal air moft confpi- 

 cuoufly in thofe parts. I was firft led into thefe reflections fome- 

 time flnce by a converfation with a friend of mine, a very in- 

 genious naturalift, who fhewed me a remarkable paflage in the 

 Bibliotheque Britannique, Tom. xxi. P. n. pag. 336. where, 

 among other extracts from the Englifh Philofophical Tranfac- 

 tions, is part of a piece of M. Defaguliers, intitled, A DifTerta- 

 2 tion 



