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XVIII. On the Ice formed, under peculiar circumstances, at the bottom of running 

 Water. By the Rev. James Farquharson, of Alford, F.R.S. 



Received March 17, — Read April 2, 1835. 



Ice formed at the bottom of rivers and streams, frequently in great quantities, is 

 a phenomenon quite common in this climate. I made for several years past a 

 number of incidental and desultory observations upon it, and became convinced 

 that the principal explanation of its occurrence is the radiation of heat from the 

 solid opake materials of the bottom ; but as I conceived this to be also the gene- 

 rally admitted one, I took no note of the observations, with the view of vindi- 

 cating the theory of the radiation. It appears, however, from a paper of M. Arago 

 upon the subject, translated and published in the Edinburgh New Philosophical 

 Journal, vol. xv. p. 123, from the Annuaire for the year 1833, that he entirely rejects' 

 the theory of the radiation of heat through a thick layer of water. In the same 

 paper, although he does not, in conclusion, pretend to give a complete explanation 

 of the phenomenon, he brings forward, as explanations in part, three circumstances, 

 which, although accurately stated by him, appear to be not exclusively appropriate 

 to ice formed at the bottom, and cannot therefore aid us in solving the main question 

 which we have to discuss here, which I apprehend to be, ff^hy is ice formed sometimes 

 on the surface of running water, and sometimes at the bottom ? 



On reading M. Arago's paper, I became desirous of offering some remarks in an- 

 swer to it, as without some one doing this, on proper data, a misapprehension con- 

 cerning the cause of a natural phenomenon, so much at variance with our most fre- 

 quent experience of the formation of ice only on the surface of all waters, as to have 

 often greatly excited the attention and even called forth the astonishment of scientific 

 men, would continue to be propagated under the authority of a distinguished name. 

 Having, however, no record of my former observations to enable me to refer accu- 

 rately to the time, place, and other circumstances of them, I delayed till a renewed 

 occurrence of ice on the bottoms of our streams should enable me to repeat them. 



Such an occurrence, on a great scale, took place in the beginning of thife month 

 of January (1835) ; and I now have the honour of presenting to the notice of the 

 Royal Society a brief account of the observations I have been enabled to make, and 

 of the conclusions to which they appear to direct us. 



Previously to entering on this detail and discussion, it seems proper to describe the 

 appearance and quality of the ice formed at the bottoms of streams. A misappre- 

 hension regarding these may have been one cause of the incredulity of its existence, 



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