ms 
Progress of the Aurora Borealis. 
to its former extent ; now runs from east to west, or from west to 
east, through 5° or 10° or 12°, during the space of a second or two 
of time, preserving correctly its parallelism with other rays, which 
it approaches or passes in its progress, then remains station- 
ary for a second or two, undergoing varies changes of vividness ; 
and afterwards disappears instantaneously, to have its place 
supplied by another ray, created as rapidly as its predecessor 
was annihilated. 
This magnificent and beautiful light gradually extends itself 
towards the south, and at length separates itself from the north- 
ern horizon, at the point of the magnetic meridan, and forms a flat 
luminous arch in the northern part of the heavens. The arch still 
goes on to make progress towards the south ; its convex or upper 
side approaching the zenith, and its concave or lower side becoming 
more widely separated from the horizon. When it reaches an 
elevation of about 45°, it presents the appearance of a broad 
zone, occupying, from north to south, the space of from 25® to 35° 
in breadth, at its vertex ; and having its eastern and western ex- 
tremities resting on the visible horizon ; and at this stage of its 
progress the eastern extremity is near the NE. point of the com- 
pass, and the western extremity a little to the north of west. 
At its extremities the zone is narrower than at its vertex ; and 
when I speak of its being from £5° to 35° wide there, it is not 
meant that its northern or southern boundaries are correctly de- 
fined, but only that the pencils of rays, when most elongated, do 
not extend beyond that space. As the rays shorten and lengthen, 
and flit and change places incessantly, the boundaries of the lumi- 
nous space are Very much indented and irregular, both towards 
the north and towards the south. 
The illuminated zone in its progress southward preserves a 
parallelism with its earlier positions ; and, after passing the eleva- 
tion of 45°, at its vertex, begins to undergo a remarkable change 
in its appearance. The pencils of shifting and varying rays, 
which, till then, occupied, in the direction of their length, a space 
of from 25° to 35°, become gradually more and more shortened, 
as the zone approaches the zenith, and the limits of the indenta- 
tion and irregularity of the southern and northern boundaries of 
the luminous space become less. The belt of light becomes 
VOL. VIII, NO. 16. APRIL 1823. 
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