Thinking that this was an error, I again wrote to the “Magazine of Natural History” as below:—­

I perceive that others beside myself have endeavoured to account for anchor frosts.  Mr. Carr says they never occur except in long and severe frosts, and that the adhesion of the ice to the stones at the bottom is owing to their acquiring a degree of cold far below the freezing-point.  He is in error when he says they never occur except in long-continued frosts, as the walls of ice which are sometimes raised on the crowns of weirs are invariably (so far as my observations have extended) deposited there before the water in the reservoir above is frozen over, which proves that the frost has not been of long continuance, although it may have been severe.  As to what he says about the stones acquiring a degree of cold far below the freezing-point, and imparting that coldness to the water, I would just ask how it is that a stone at the bottom of a river acquires this excess of cold, and if it is not more probable that the stones impart warmth to the surrounding water?  I can easily conceive how the stones may, by the action of the sun’s rays upon them, warm the surrounding water; but I do not see how they can impart cold, or, in other words, how their temperature can be reduced below that of the water by which they are surrounded.  Stones certainly impart warmth to the water they are in, in bright weather, as the rays of the sun do not give much warmth in passing through any transparent medium; but on coming in contact with any opaque bodies, the heat is absorbed or reflected as the case may be, and in this way transparent media such as air and water acquire a warmth by contact which they would not otherwise possess.  Thus, if an anchor frost is followed by a bright day, the rays of the sun impart so much warmth to the stones at the bottom of the river as is sufficient to liberate the ice from them, and on such days thousands of pieces of ice may be seen rising from the bottom and floating down the streams.

Since my former observations were written I have had the satisfaction of finding my views on the subject confirmed by a very eminent chemist, [15] and if the discussions in your Magazine were to be settled by authority, and not by argument (which I trust will never be the case), he is one to whom many would be inclined to appeal, and to whom few would refuse to submit. (May 2nd, 1832.)

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To the Editor of the “Agricultural Gazette.”

In a leading article of the 10th of January, 1852, after an account of the effects produced on water by radiation and the protection afforded to plants by the ice with which ponds are covered in winter, you go on to say that there are some circumstances under which water-plants suffer greatly, and from a singular cause, but one which when looked into is sufficiently simple and intelligible.  As you do not appear to have hit upon the true reason, allow me to quote a little further, and then give my reason for this singular effect.