366 Rev. Mr Rarquharson on the Appearance and 
gradually more compact, and its vividness greater. The pencils 
of rays upon the magnetic meridian, still continue directed to- 
wards the zenith, and those considerably to the eastward or 
westward of that line are still directed either to the zenith,, or 
to a point a little southward of it ; and, therefore, changes gra- 
dually the angle which they make with the zone. At the same 
time, both the eastern and western extremities of the arch gene- 
rally becomes gradually elevated above the visible horizon ; a 
circumstance which frequently takes place, with regard to one 
or both of them, at an earlier stage of the progress southward. 
At length the luminous zone reaches the zenith, and coincides 
in its whole extent, from east to west, with the Prime Vertical, to 
the magnetic meridian ; and the changes described in the last 
paragraph having gone on continuously, it now presents an. ap- 
pearance tvhich deserves a particular description. It is very 
narrovf, in comparison with what it was when in the earlier stages 
of its progress, not exceeding in breadth from north to south 
more than 3° or 4°, or at the most in its widest parts 5°. It has 
its boundaries better defined both to the south and north ; for it 
now vanishes off entirely from its compactest central light, with- 
in the limits of 1°. The intensity of the light is now greatly in- 
creased, and, near the zenith, the light no longer shews parallel 
rays, but exhibits a nebulous or mottled appearance, varying 
incessantly in intensity,, by tremulous flickerings, in undefined 
small patches. Towards the east and west of the zenith, the light 
assumes a mixed character, partaking of the nebulous appear- 
ance, and of the appearance of parallel rays; the latter gradually 
prevailing in proportion to the distance from the zenith, and be- 
coming perfect towards the extremities of the zone ; and as the 
rays still point towards the zenith, or a little southward of it, 
they are now parallel, or nearly so, to the line of the zone. At 
this period both extremities are generally elevated above the 
horizon, sometimes 25° or 80°, sometimes more. Sometimes one 
of them is very little elevated, not more perhaps than 5° or 10°, 
and the other extends very little beyond the zenith, for in this 
respect the zone is exceedingly various. 
The luminous space still continues to move southwards, pre- 
serving its parallelism with its earlier positions ; and, after it has 
reached 5° or 10° to the southward of the zenith, it begins to 
