( ) 
The next Section is the principal, and is engag’d 
in explaining the feveral particular Appearances of the 
Lumen Boreale , fuch as its Situation, ordinarily to- 
wards the North , declining a little towards the Wejt ; 
its dark, dufky, circular Bafis, furmounted fome- 
times with one or more luminous Arcs ; from behind 
which Columns, or Streams of Light, feem to iffiie 
either perpendicularly or concentric with the Ares } : 
add to thefe the Rainbow-Colours, Flalhes, Vibrati-i 
ons, and in the laft Place, a Glory, Canopy, or 
Corona , form'd by a Concourfe of the Rays of the 
Matter of this Phenomenon, near the Zenith of the. 
Place. 
Mr. M air an premifes an Inveftigation of the Lo-. 
cus, or Limit of the Attractive Forces of the Sun and 
Earth, fo that a Particle of Matter placed any where 
in it, will be equally attracted by both, or tend as 
much towards the Earth as it does towards the Sun. 
He finds, that if in a Line connefting the Centres of 
the Sun and Earth, a Point be taken at the Di- 
ftance of about 43 Semidiameters of the Earth from 
her Centre, that Point will be in this Limit, fo that 
a Particle placed there, will not gravitate either to- 
wards the Sun or Earth, but remain in ^ 'Equilibria , 
the equal and contrary Forces of the Sun and Earth 
deftroying each other. The Ufe he makes of this is 
to Ihew, that an Aurora Borealis may poflibly be 
formed by aDefcentof the Zodiacal Matter, lying 
between this Point of ^Equilibrium and the Earth ; 
tho’ it does not reach fo far as to involve the Earth 
itfelf. But the Aurora in this Cafe will be an in- ~ 
compleat and particular one. 
The 
