( 4*5 ) 
ftill more and more oblique, as the Diftance from the 
Poles is greater, i o this we beg leave to fiippofe, that 
this fubtile Matter, no otherways difcovering it felf but 
by its EfFedts on the Magnetick Needle, wholly imper- 
ceptible and at other times invifible, may now and then, 
by the Concourfe of feveral Caufes very rarely coinci* 
dent, and to us as yet unknown, be capable of produ- 
cing a fmall Degree of Light ; perhaps from the greater 
Denfity of the Matter, or the greater Velocity of its Mo- 
tion ; after the fame manner as we fee the Effluvia of 
EleElrick Bodies by a ftrong and quick Fricftion emit 
Light in the Dark : to which fort of Light this teems to 
have a great Affinity. 
This being allowed me, I think we may readily affign 
a Caufe for many of the ftrange Appearances we have been 
treating of, and for fome of the moft difficult to account for 
otherwife ; as why thefe Lights are rarely feen any where 
elfe but in the North, and never, that we hear of, near 
the Equator : as alfo why they are more frequently feen 
in Iceland and Groenland , than in Norway, though nearer 
the Pole of the World. For the Magneticai Poles, in this 
Age, are to the Weflward of our Meridian, and more fo of 
that of Norway, and not far from Groenland ; as appears by 
the Variation of the Needle this Year obferved, full 
twelve Degrees at London to the Weft. 
The ered Pofition of the luminous Beams or Stride fo 
often repeated that Nighr, was occafioned by the rifing 
of the Vapour or lucid Matter nearly perpendicular to the 
Earth’s Surface. For that any Line erecfted perpendicu- 
larly upon the Surface of the Globe, will appear ereft to 
the Horizon of an Eye placed any where in the famefpbe” 
rical Superficies ; as Euclid demo nft rates in a Plain, that 
any Line ere&ed at Right Angles to it, will appear to be 
perpendicular to that Plain from any Point thereof. ^ hat 
it ihouid be fb in the Sphere is a very pretty Proportion, 
not 
