The waters in the pools between the rapids of rivers can hardly ever be still enough for the water to fall below the freezing-point and yet remain fluid; the temperature of water in such situations is not below 33 degrees.

The following was my rejoinder:—­

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.