( «45 ) 
Fire, and fliot its Streams or Flames perpendicularly 
upwards, which being undihurb’d by Winds, muft ap- 
pear flreight and pointed at the Top. The Bafes mud 
make an Arch by the Rules of Perfpecdive: For, I 
think, an Horizontal Right Line, of a vaft Length, and 
at a great diftance from us (fuch as I take the Northern 
Edge of this luminous Cloud to have been,) feen at a 
confjderable height in tlie Air, mud appear bent down 
into an Arch. On a fuddenthc Fire propagated it felf 
to all parts of this Vapour. The whole Heaven mud 
then appear cover’d with the fame Streams, which tho’ 
really parallel to one another, mud appear bent into a 
Cupola. The diooting and darting ol thefe Flames, and 
their Concourfe, together with a Smoak proceeding 
from them, mud give that confus’d Cloud which was 
obferved in the Center of this Canopy. The regular Dif- 
pofition of the Colours in every Stream, perhaps, you 
may account for. I think, the Red appear’d at the right 
hand in all of them. Somewhere in the ? hilof.tr 
I have met with an Obfervatian of an Aurora^ in which 
the Streams were colour’d only where they met, or' 
crofs’d one another. Whether the Light of one Stream 
pading thro* another, may not be feparated into Co- 
lours by Refra(dion, 1 will not determine. You may 
think of a better Solution. If the Altitude of the Top 
of the Arch in the North had been taken here, and at 
the fame time at another Place upon the fame Meridian, 
whofe didance is known, from thence I imagine, the 
Height of the Cloud fas I call it) might have been cal- 
culated. 
I am, 
Hallen. 
