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.") * * * * * ON THE PRODUCTION OF ICE AT THE BOTTOMS OF RIVERS. The phenomenon of the production of ice at the bottoms of rivers has been repeatedly noticed, but I am not aware that any satisfactory solution of the cause has hitherto been given. In Nicholson's "Dictionary of Chemistry," several different hypotheses are enumerated, which I shall not stop now to examine, since it may be safely asserted that they neither accord with the established principles of chemistry, nor with the facts for which they endeavour to account. The most recent theory with which I am acquainted is that of Mr. A. Knight, who in a paper lately published in the "Philosophical Transactions," seems to consider the particles of ice as originally formed at the surface, and afterwards absorbed by the eddies of streams to the bottom. He states, in support of this idea, that he did not observe any similar phenomenon in still water. I shall advert to this hypothesis in the sequel, and at present it may suffice to remark of it and all others which I have hitherto seen, that supposing any of them to be correct, the same effects ought regularly to be produced whenever the atmosphere is at a similar temperature, or in other words, that whenever the frost is so intense as materially to affect the water of a river, we may then expect to find ice at the bottom. Now this is certainly not the case, since the appearance we are treating of never occurs but under peculiar _atmospherical_ circumstances, and rivers are frequently frozen over, and remain so for a length of time without a particle of ice being visible at the bottom of their streams. I do not now profess to have developed this mystery, but merely intend to state the circumstances under which the phenomenon takes place, as well as a