of a glass vessel filled with water? Well, clear air and
fog seemed to behave towards each other pretty much the
same way as milk in that case behaves towards water.

I am rather emphatic about this because I have made a
study of just such mists on a very much smaller scale.
In that northern country where my wife taught her school
and where I was to live for nearly two years as a
convalescent, the hollows of the ground on clear cold
summer nights, when the mercury dipped down close to the
freezing point, would sometimes fill with a white mist
of extraordinary density. Occasionally this mist would
go on forming in higher and higher layers by condensation;
mostly however, it seemed rather to come from below. But
always, when it was really dense, there was a definite
plane of demarcation. In fact, that was the criterion by
which I recognised this peculiar mist. Mostly there is,
even in the north, a layer of lesser density over the
pools, gradually shading off into the clear air above.
Nothing of what I am going to describe can be observed
in that case.

One summer, when I was living not over two miles from
the lakeshore, I used to go down to these pools whenever
they formed in the right way; and when I approached them
slowly and carefully, I could dip my hand into the mist
as into water, and I could feel the coolness of the misty
layers. It was not because my hand got moist, for it did
not. No evaporation was going on there, nor any condensation
either. Nor did noticeable bubbles form because there