The aspect of the
phenomenon depends also upon the positions of the observers. The seat
of the aurora borealis is in the upper regions of the atmosphere;
though sometimes it appears to be produced in the less elevated regions
where the clouds are formed. This, at least, is what follows from some
observations, especially from those of Captain Franklin, who saw an
aurora borealis the light of which appeared to him to illuminate the
lower surface of a stratum of clouds; whilst some twenty-five miles
farther on, Mr. Kendal, who had watched the whole of the night without
losing sight of the sky for a single moment, did not perceive any trace
of light. Captain Parry saw an aurora borealis display itself against
the side of a mountain; and we are assured that a luminous ring has
sometimes been perceived upon the very surface of the sea, around the
magnetic pole. Lieutenant Hood and Dr. Richardson, being placed at the
distance of about forty-five miles from each other, in order to make
simultaneous observations, whence they might deduce the parallax of the
phenomenon, and consequently its height, were led to the conclusion
that the aurora borealis had not a greater elevation than five miles.
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