r «5o ) ‘ 
irom the S.S.K. and fo leiTen’d till it appear’d no brigh- 
ter than the Milky Way, but more like a very thin 
Cloud or Mid, thro’ which I could perceive the Stars. 
At the fame time I faw another thin Cloud, having 
the fame Appearance, Arch-ways, to the Southward, 
at about the Height of 40 Degrees, which I fuppofe 
had been another, which had been over, and had 
moved thither from the Northward before I went out ; 
And during the whole time there were lefTer Lights 
towards the North, but difperfed here and there, and 
not lorming any large Body of Light. During the 
whole time, the Hemifphere was clear, except a few 
very fmall Clouds near the Horizon ; and when any 
moved into the enlighten’d Arch, they broke the Con- 
nexion , fo that the Light was above them : At the 
fame time it froze hard each Night. 
From thefe Obfervations, I fuppofe that the Aurora 
Borealis is a thin Nitro-fulphureous Vapour rais’d in our 
Atmofphere confiderably higher than the Clouds, which 
is difeontinued in fcveral Places by the interfpers’d 
Air, and which by PrclTure and Motion is kindled ; 
and perhaps the txplofion of one may by its Shock 
andMotion contribute to kindle the next,* by which 
means they go off' one after another, till the whole 
Vapour within their Influence is difeharged, and then 
the Light difappears, and the thin Smoak appears, and 
undulates, according to the Motion in that part of the 
Atmofphere. And hence I think, mod of the Appear- 
ances may be folv’d : For i/?, As to the continu’d 
Light near the Horizon, they being at a great diftance 
from us, and nearly in a Line, all thefe Exploffons may 
feem as a continued Light : When thefe approach nea- 
rer to us, and by confequence appear higher^ in our 
Hemifphere, we obferve the Motion in each Flafli, and 
dill feeing them laterally, yet fomew^hat breaking the 
Con- 
