46 



iron, and a corresponding quantity in the scales of oxide detached 

 from its cavities. 



On Ice found in the bottoms of Rivers. By Thomas Andrew Knight, 

 Esq. F.R.S. In a Letter addressed to the Right Hon. Sir Joseph 

 Banks, Bart. G.C.B. P.R.S. Read May 23, 1816. [Phil. Trans. 

 1816,;?. 286.] 



The author having witnessed this phenomenon in the course of 

 last winter in the river Teme, which runs past his residence in Here- 

 fordshire, describes the appearances that he observed, and relates the 

 circumstances under which they occurred, for the purpose of account- 

 ing for a fact which, though frequently noticed, has not yet been 

 satisfactorily explained. 



After a night that had been intensely cold, the stones in the rocky 

 bed of the river glistened with a kind of silvery whiteness, which, 

 upon examination, arose from numerous spicula of ice adhering to 

 them, and crossing each other in every direction. The river was not 

 at that time frozen over in any part, but the temperature of the water 

 was at the freezing point ; and in a mill-pond just above, the water 

 was replete with millions of spicula of ice, which naturally would 

 have a tendency to rise and form a crust at the surface ; but in fall- 

 ing over a low weir into a narrow channel, numerous eddies, occa- 

 sioned by large projecting stones, constantly carried fresh spicula to 

 the bottom, where they collected against the surfaces and in the 

 cavities opposed to the current, especially in those parts where it 

 became less rapid. 



Had the coldness of the weather continued, it is conceived that 

 the ice might have continued to accumulate to much larger quanti- 

 ties, as it had been known to do in the same situation some years 

 preceding, when the frost was of long duration. 



It was remarked by Mr. Knight, that near the shore the ice that 

 adhered to stones partly out of the water had a firmer consistence, 

 although apparently originating from the same source. This ice ex- 

 tended as far as half a yard from the shore, and was three or four 

 inches below the surface of the water. This did not melt so rapidly 

 as that which was deposited at greater distances from the sides, and 

 at greater depths. 



Although the existence of porous ice in any large quantities may 

 thus be explained in larger rivers, where there are eddies sufficient 

 to carry floating spicula in contact with the bottom, yet the author 

 expresses his doubts respecting large masses of solid ice said to have 

 been found at the bottoms of deep and sluggish rivers, in which there 

 are no eddies to cause the descent even of small particles, and no 

 obvious cause of subsequent consolidation. 



