with
moisture. What really spreads, is the cold air which by mixing with,
and thereby cooling, the warmer, moisture-laden atmosphere causes
the condensation. That is why our fall mists mostly are formed in an
exceedingly slight but still noticeable breeze. But in the case of these
northern mist pools, whenever the conditions are favourable for their
formation, the moisture of the upper air seems to be pretty well
condensed as dew It is only in the hollows of the ground that it remains
suspended in this curious way. I cannot, so far, say whether it is due
to the fact that where radiation is largely thrown back upon the walls
of the hollow, the fall in temperature at first is very much slower
than in the open, thus enabling the moisture to remain in suspension; or
whether the hollows serve as collecting reservoirs for the cold air
from the surrounding territory--the air carrying the already condensed
moisture with it; or whether, lastly, it is simply due to a greater
saturation of the atmosphere in these cavities, consequent upon the
greater approach of their bottom to the level of the ground water. I
have seen a "waterfall" of this mist overflow from a dent in the edge of
ground that contained a pool. That seems to argue for an origin similar
to that of a spring; as if strongly moisture-laden air welled up from
underground, condensing its steam as it got chilled. It is these strange
phenomena that are familiar, too, in the northern plains of Europe which
must have given rise to the belief in elves and other weird creations of
the brain--"the earth has bubbles as the water has"--not half as weird,
though, as some realities are in the land which I love.

Now this great, memorable fog of that November Friday shared the nature
of the mist pools of the north in as much as to a certain extent it
refused to mingle with the drier and slightly warmer air into which it
travelled. It was different from them in as much as it fairly dripped
and oozed with a very palpable wetness. Just how it displaced the air in
its path, is something which I cannot with certainty say. Was it formed
as a low layer somewhere over the lake and slowly pushed along by a
gentle, imperceptible, fan-shaped current of air? Fan-shaped, I say;
for, as we shall see, it travelled simultaneously south and north; and
I must infer that in exactly the same way it travelled west. Or was it
formed originally like a tremendous column which flattened out by and
by, thr