You say at the end of remarks about bottom-ice that you cannot
admit the soundness of my explanation, and that you are well aware
of what is said by Arago and others on this curious phenomenon,
and that bottom-ice has been observed in ponds when there was no
breeze, and that the water in pools between the rapids of weirs
can hardly ever be still enough to fall below the freezing-point,
and yet remain fluid.
I was not aware before seeing your remarks that either Arago or
any other philosopher had ever written about bottom-ice, and even
now I do not know what are their opinions on the subject, and if
the discussions in your paper are to be settled by authority and
not by argument, I can only make my bow and withdraw; but if it
meets your views to allow your correspondents to state their
opinions temperately, and support them by such arguments as occur
to them, I do not yet feel inclined to give up my notions about
bottom-ice. Will you allow me to ask whether you ever personally
saw ice at the bottom of a pond when there was none on the
surface? and if so, under what circumstances? I have heard of such
an occurrence, but never witnessed it, and feel inclined to doubt
the fact unless you will vouch for it; for it appears to me that
the moment the water at the bottom falls below 40 degrees it will
begin to rise to the surface, and it is so excellent a conductor
that it will instantly equalize the temperature of the mud at the
bottom with that of its own temperature.
I am neither chemist nor meteorologist, and therefore I am not
able to say much about radiation; but my idea of it is, that its
effects in water would be much greater in still pools than in
rapid streams, and that, therefore, if radiation was the cause of
bottom-ice, there ought to be more of it in the pools than in the
rapid streams. But the contrary is the fact, for after a severe
night's frost, I can frequently find the streams filled with this
bottom-ice, when none can be observed in the pools.
Again, can the fact of the weir which had a wall of this bottom-
ice three feet high in a single night, be accounted for by
radiation? It appears to me to be very easily accounted for by
supposing that the water in the deep above was so quietly cooled
down as to retain its fluidity until the shaking it got on flowing
over the weir suddenly produced congelation. I think that
radiation would not go on at the crown of the weir alone.
Why do you think that the water in pools is never still enough to
allow it to get below 32 degrees without freezing on still clear
nights? In long deep pools, where the body of the water is perhaps
a hundred times as great as the current flowing into it, the
motion is so extremely slow that I cannot for a moment doubt that
it gets below 32 degrees without congelation, but when it arrives
at a rapid, this ice is immediately formed.
The Editor closed the discussion at this point by saying that the
subject was not of sufficient agricultural importance to be
continued further.
The following is my brother Richard Garnett's [16] account of his
observations on bottom-frosts. (The paper was written in 1818, and
published in the "Journal of the Royal Institution.")
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